The Garden Shed
A Community Newsletter published by the Piedmont Master Gardeners
April 2024, Vol.10,No.4
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Table of Contents
Feature
Drip Irrigation Systems for Home Gardens
These systems are no longer just for commercial nurseries and farms
In the Edible Garden
Peat-free Potting Mix: What are the Best Options?
Reducing peat moss use in potting mixes can help reduce climate change, but what should we use to replace it?
Tasks and Tips
In April our spring gardening season hits full stride. This article provides guidance and sources to help gardeners get the best results from their vegetable and fruit growing efforts this year.
Drip Irrigation Systems for Home Gardens
Although in the Charlottesville area we get a good amount of rain throughout the year, still there are dry periods during the growing season when our plants may suffer if they don’t receive additional irrigation. For the reasons explained below, there are many advantages when home vegetable and landscape gardens are irrigated using drip irrigation rather than hand watering or spray-irrigation methods. Please note that this article is intended as a general guide for home garden irrigation only, which excludes home lawns or commercial agriculture, because they have different system requirements. Detailed information on the topics discussed here are available on the websites listed in the reference section at the end of this article. Also, the Piedmont Master Gardeners Help Desk is available to answer any questions that you may have. The best way to send your questions to us is by email at albemarlevcehelpdesk@gmail.com.
I installed my first drip irrigation system when I lived in California. At that time, local water conservation regulations limited landscape irrigation to twice a week during certain days and times. I decided to convert my lawn to a garden of mainly native plants that could be irrigated by a drip system for water conservation. During my research I became aware that, in addition to water conservation, drip irrigation (also called micro-irrigation) had many other advantages. Although professional installation of drip systems is available, most home gardeners should be able to plan, install, and maintain their own drip irrigation system after doing some research.
Benefits of Drip Irrigation
Drip irrigation system on a raised vegetable bed. Photo: Khosro Aminpour
A drip irrigation system with a timer can be programmed to automatically deliver water from a suitable water source through a network of plastic tubes and emitters to the root zones of landscape plants. The timer can be programmed for start time (say 6:00 AM); run time (say 15 minutes); and frequency (say once every 3 days). Having full control over the time and amount of water delivered to each plant, the gardener will benefit as follows:
- Water is delivered directly to the root zone, eliminating runoff, overspray, excessive evaporation, and over-watering. Significant water conservation is achieved by this method.
- Full control over watering amounts and frequencies result in consistently uniform soil moisture, and therefore healthier plants.
- Flowers, leaves, and stems of plants stay dry and are less susceptible to fungal diseases.
- Weed growth is minimized in bare areas of the landscape beds because they are not watered.
- Very early in the morning is the best time to irrigate plants, and this is easily achievable by setting the start time on the timer.
- Drip irrigation is very versatile and can be configured to water a variety of landscape shapes and sizes. A single potted plant, a vegetable garden, annual and perennial beds, and young trees can all be connected to a drip irrigation network. You can start with a small project and as you gain experience, and when needed, the same system can be gradually expanded as necessary.
- Drip irrigation pipes are typically laid on the ground and don’t require digging. They can easily be re-configured as needed to accommodate any changes. Repairs are also very easy due to the same reason.
- Timers with multiple outlets allow for zoning of plants with differing watering needs. Each zone can be programmed for its optimum frequency and run time.
Drip Irrigation System Components
A wide range of materials and equipment from simple to very sophisticated are available on the market. Here I have briefly described what I used for my garden, and I think will sufficiently serve most home gardens. Details, photos, and specifications of each component are readily available on the internet for interested gardeners.
Components are connected together either by hand-tightening of screw joints; pushing together of compression joints; or punching a hole in the tubes and inserting emitters. Not many tools are needed and most of them you probably have. The only tool that you will probably need to buy is a tube hole-punch.
The basic components of a typical home garden drip system are:
- A reliable water source with clean water at a pressure of at least 25 PSI (Pounds per Square Inch), such as a regular wall hose bib. Municipal water is generally suitable for use in drip irrigation. If you use well water, special attention should be paid to suspended or dissolved elements that can cause clogging of small pipes and fittings. These elements may include minute suspended particles that can pass through the filter (such as in murky water); algae; or dissolved compounds of calcium and magnesium that have a tendency to get deposited within the system.
- A brass 2-way Y connector with shut off valves. One branch is used to connect the drip irrigation control assembly and the other is for a regular hose connection in case needed for other purposes.
- A battery-operated timer. A timer is used to automatically start irrigation and run for preset times and frequencies. Timers are available with up to four outlets, each for a different irrigation zone.
- A backflow preventer. This device prevents any potentially contaminated water left in the drip system from reentering the house water supply system, and is necessary for health reasons.
- A pressure regulator. This device reduces the source water supply pressure (which is typically between 40 to 60 PSI) to 25 PSI, which is the recommended safe water pressure for most drip irrigation components and joints.
- A filter. A filter captures any small particles that may be present in the water supply lines and prevents the clogging of dripper holes. Filters need to be inspected and cleaned periodically.
- A tube adapter. All the above parts have screw type joints which are hand tightened. The tube adapter has one end as a screw joint and the other end as a compression joint, which allows a drip tube to be connected.
- Distribution tubes. Distribution tubes consist of a combination of various size tubes commonly made of polyethylene. They convey water from the control assembly (items 1 – 7 above) to points near each plant. Mainline tubes make up the backbone of the network and may be made up of ½ or ⅝ inch diameter tubes. They are laid on the soil surface along the perimeter of the garden or snaked through it to reach the maximum number of plants without having too many elbows or sharp bends. The ¼ inch tubes, also called microtubes, can branch off from mainlines to deliver water to plant root zones. Emitters (as described below) can be installed at any point along mainlines or microtubes. The length of each mainline from the control assembly to the farthest end of that mainline should not be more than 200 feet; the total flow rate should not exceed 120 GPH (gallons per hour). Microtubes should be limited to 25 feet in total length (measuring from its connection with a mainline to the farthest end of the microtube), and its flow should not exceed 12 GPH.
- Driplines are ¼ or ½ inch diameter tubes with embedded emitters at equal spacing. They are used for row crops such as vegetable gardens or around trees. Soaker tubes are made of porous rubber and discharge water all along their length. Their rate of discharge is not predictable and therefore are not widely used; however, they may be useful under special circumstances.
- Emitters. Emitters deliver water to plants at a pre-set rate. They are small plastic parts that are inserted into mainlines and/or at the end of microtubes and discharge water at the point of delivery. Emitters of different sizes are identified by their GPH ratings, and some common ratings are 0.5, 1.0, and 2.0 GPH. I personally prefer to use 2.0 GPH emitters as much as possible because they are less prone to clogging than smaller ones. There are two types of emitters, i.e. pressure compensating and pressure sensitive. Pressure compensating emitters deliver the nominal flow rate irrespective of changes in water pressure caused by elevation changes or friction losses in the mainlines. Pressure sensitive emitters do not have this ability. There are many other types of emitters on the market such as spray emitters and adjustable flow emitters, which may be useful in special situations.
- Fittings. The availability of many fittings for mainline and micro tubes makes the drip irrigation system very versatile, and allows for easy repairs. Such fittings include elbows, tees, couplings, end caps, and adapters of different sizes.
Drip irrigation graphic by Jess Stryker, reprinted with permission, Sprinkler Warehouse.
Setting the Timer
The goal in establishing a watering routine is to keep the soil uniformly moist (not too dry and not too wet) during the dry season in such a way that plants don’t show any signs of under- or over-watering (wilting, scorching, yellowing leaves, or leaf drop). A simple method for setting the timer is to estimate an initial frequency and run time on the timer and observe the results in the garden. Then adjust the timer and/or number of emitters until you find the optimum setup after a few iterations. As a rule of thumb, watering 2 or 3 times a week totaling about 1 inch of water is enough to keep most plants happy. However, several factors, including atmospheric conditions, soil type, plant type, plant maturity, etc. make this method approximate. A more accurate method is to follow the step-by step procedures described in the Appendix at the end of this article.
Drip Irrigation System Maintenance
Drip irrigation system components are delicate and can be easily damaged and lose their proper function. Regular inspection and timely maintenance, which are easy to do, will ensure delivery of adequate water to your plants. Maintenance at the beginning of each growing season includes putting new batteries in the timer; setting timer parameters; checking the filter to make sure it is clean and not damaged; flushing the main lines and checking for any leaks along the main and micro tubes; and checking all emitters to identify and replace clogged ones.
During the growing season, occasionally check the timer battery and filter; periodically check soil moisture and make timer adjustments if necessary; check plants for any signs of inadequate or excessive watering; check for any damaged main or micro tubes and make necessary repairs; and cover main lines with mulch to protect them against the elements.
At the end of the growing season, remove the control assembly and store it in a dry and clean location for the following year; remove timer batteries; clean the filter; flush the main lines after removing the end caps; drain the main lines and replace the end caps.
Final Thoughts
My own experience with installing and using a drip irrigation system was very positive, and I hope it will be just as positive for other gardeners. In view of growing concerns about plastic pollution in agriculture, it should be noted that the polyethylene tubes used in drip irrigation systems can be recycled at the end of their lives. See “The Basics of Micro-Irrigation,” (2023) (“Drip tubing is typically made from polyethylene plastic that can be recycled. Some drip tubing manufacturers offer recycling of tubing, hose or tape.”)
APPENDIX:
For the most accurate method of setting the timer, use the formulas set forth below, which take into account the loss of moisture to the atmosphere:
Moisture is lost to the atmosphere from soil surfaces and plant leaves. Rain replenishes some of the lost moisture but during periods of draught soil moisture should be maintained at the optimum level by irrigation. The following paragraphs explain how to estimate and supply the correct amount of irrigation water in the absence of rain during the growing season. Plants should receive enough water to compensate for the loss of moisture to the atmosphere through evaporation from soil within their root zones, and by transpiration from their leaves. The sum of these two quantities is called evapotranspiration (ET). ET depends on many factors, including solar radiation, temperature, humidity, wind, and plant type, and varies throughout the year. Calculating ET for any given situation and time requires processing large amounts of data and is very complicated and time consuming. However, we can make educated estimates. These estimates can then be verified by periodically measuring soil moisture and adjusting the amount of water supplied. This method can provide an accurate and practical tool for home gardeners. The best available study for ET that can be used for Albemarle/Charlottesville area was done by the Northeast Regional Climate Center (NRCC) and its results are available on the Cornell University’s website at the following link: https://www.nrcc.cornell.edu/wxstation/pet/pet.html . The study area does not cover Virginia, however, the proximity of Washington DC to Albemarle County and the similarity of climates can justify using the DC numbers as the best estimate for Albemarle county.
—-Estimating Evapotranspiration (ET) – According to the Cornell study, the highest potential average ET for Washington, DC occurs in the month of July and is 4.66 inches per month, or 0.15 inch per day. We can use this number for Albemarle County as well.
—-Estimating daily water demand – The daily water demand for any given planted area is equal to its daily evapotranspiration (ET) and can be calculated by the following formula:
Note: In the following formulas, the number 12 is to convert inches to feet, and the number 7.48 is to convert cubic feet to gallons.
Daily water demand (gallons per day) = (0.15 ÷ 12) x Area* (in square feet) x 7.48
Thus, for a 32 square foot vegetable garden, the daily water demand will be:
(0.15 ÷ 12) x 32 x 7.48 = 2.99 gallons per day.
∗ For plants spaced closely together such as vegetable gardens, “Area” is the total planted area; while for individual shrubs or trees spaced apart, “Area” is the surface area under the plant canopy. It is not necessary to calculate areas for each individual plant; rather, plants should be divided into different categories of approximately equal drip-line area such as annuals and perennials, shrubs, trees, etc., and an average area designated to each category.
Controlling water supply – Water supply can be controlled by adjusting settings on the timer and/or selecting the size and number of emitters. Timer settings control water to the whole zone, while the size and number of emitters only affect an individual plant or a section of the planted area. In order to ensure that the water supply adequately meets the water demand, follow the procedure described below, paying attention to units of days, hours, or minutes:
—-Zone flow rate – Multiply the number of emitters in the zone by their nominal flow rate (in gallons per hour) and convert to gallons per minute. For example, if there are 32 emitters with a flow rate of 2 gallons per hour, the zone flow rate will be (32 x 2) ÷ 60 = 1.07 gallons per minute. If there are several emitter sizes in one zone, repeat the same operation for each size and add all together.
—-Watering frequency (how often) – Decide on how often you want to water your plants. Typically, shallow rooted plants such as vegetables and annuals require more frequent watering (daily or once every two days), while deeper rooted plants such as established perennials, shrubs, and trees can do well with less frequent watering (once every two to three days or even more). In the following formula, for “watering frequency“ use 1 for everyday watering, 2 for once every two days, 3 for once every three days, etc.
Run time or watering duration (how long) – To calculate the run time, use the following formula:
— –Run time (minutes) = Daily water demand (gallons per day) x watering frequency ÷ Zone flow rate (gallons per minute)
——In the example above for Estimating Daily Water Demand, the daily water demand was calculated to be 2.99 gallons per day, and let’s say watering frequency is 2, with zone flow rate of 1.07 gallons per minute.
The run time will be: (2.99 x 2) ÷ 1.07 = 6 minutes.
— The calculations above provide an estimate for the initial setting of the timer. With the help of a soil moisture meter, and periodic observations, determine if your plants receive enough water or not; and if necessary, adjust your timer settings and/or the number and size of your emitters. Also remember that plant daily water demand changes with climatic conditions throughout the year. For example, the NRCC study referenced above shows that ET for Washington, DC during April and October are 2.73 and 1.89 inches per month or 0.09 and 0.06 inches per day respectively. These numbers should be used for ET instead of 0.15 if we want to calculate the daily water demand for April and October respectively. ET for the months of May to September, inclusive, are fairly constant, around 4.66 inches per month.
SOURCES:
Featured Photo: Khosro Aminpour
“Drip Irrigation,” University of Rhode Island
“Drip Irrigation for Home Gardens,” Colorado State University Extension
“Drip Irrigation for the Yard and Garden,” Washington State University Extension (free download)
“Drip Irrigation: The Basics,” University of Arizona Cooperative Extension
“Agricultural plastics as a potential threat to food security, health, and environment through soil pollution by microplastics: Problem definition,” www.sciencedirect.com, Science of the Total Environment (Vol. 892, September 2023)
“The Basics of Micro-Irrigation,” (University of Wisconsin 2023) (“Drip tubing is typically made from polyethylene plastic that can be recycled. Some drip tubing manufacturers offer recycling of tubing, hose or tape.”)
Peat-free Potting Mix: What are the Best Options?
Since the 1940s or 1950s peat moss has been a widely-used component of potting soils and related commercial soil mixes. However, as noted in the Garden Shed article Should We Stop Using Peat?, peat bogs, which account for 3% of the earth’s surface, provide 15-30% of land-based carbon storage. Unfortunately, digging up peat moss releases much of that stored carbon into the atmosphere, contributing to climate change.
Many climate-sensitive gardeners would like to convert to peat-free potting soils. However, exactly what to change to is confusing, and the many different mixes on the market make it unclear what the best alternatives are. Let’s take a look at market choices and Cooperative Extension recommendations to try to determine the best options.
Key Functions of Growing Media
There are several potting mix characteristics that are important to its success as a growing medium:
- Supplying plant roots with nutrients, air and water. Most require some fertilizer additions.
- Allow root growth
- Provide physical support to growing plants
- Be free of pests, pathogens and weed seeds
- Have a pH appropriate for the plants to be grown.
Peat moss supports several of these elements, including lightening soils, allowing air and water entry, and holding moisture without over-saturating the plants. Its key weakness is that it lacks necessary nutrients, typically requiring the addition of other organic materials and/or fertilizers. Also, it tends to have a low pH and may require the addition of lime to reduce acidity. Certainly, any replacement material or mix of materials should perform as well as peat-based products in these areas.
What is available commercially?
An examination of local dealer inventories shows a head-spinning variety of options. Many still offer products that include some amount of peat. Products include varying combinations of multiple materials including peat moss, reed-sedge peat (a darker, more decomposed material from reeds, sedges and grasses), recycled forest products, rice hulls, perlite, vermiculite, coconut coir (pronounced coy-er), worm castings, fertilizers, and limestone (to adjust pH).
Example of coir growing mix. Photo: R Morini
Examples, without including brand names, include:
- 50-70% coconut coir plus 30% perlite and fertilizer
- 50+% forest product (tree bark and ground wood) plus peat or compost, perlite and fertilizer
- Various mixes that may include forest products, reed sedge peat, rice hulls, perlite, limestone.
- Compost-based materials including worm castings, bat guano, ground oyster shells, feather meal, soybean meal, bonemeal, lobster meal, kelp meal and other additives that are local to the manufacturer location.
Obviously, the best substitute for the long-established peat-based potting mixes isn’t clear, and in fact, may vary by intended use and location, but there are a number of non-peat products available for trial.
What do the Cooperative Extension Services recommend?
There are specific recommendations available from multiple Extension Services, but before getting specific, it probably makes sense to note the benefits and drawbacks of the various components already mentioned:
- Based on published articles, the most favored non-peat primary components are coconut coir and ground tree bark/wood.
- Coconut coir is the most-recommended non-peat component.
- Almost all of the new potting soils on the market recommend adding compost to the mix. Compost adds missing nutrients while supporting the other necessary functions of the potting soils. In fact, using straight local or home-made compost as a potting soil for vegetables, herbs, and flowers is one recommended solution.
- Items like builders’ sand, perlite, and vermiculite help boost air and water accessibility, but add little or no nutrients and may drain moisture faster than desirable.
- While fertilizer needs vary according to other ingredients, some amount is generally needed, and organic products like bone meal, blood meal, and fish meal are among the preferred additions.
- pH can vary significantly, and pH preferences will depend upon the plants to be grown. A lime-based fertilizer is often recommended to raise pH and reduce acidity. Sulfur-based products can increase acidity as needed.
Ground coco coir. Photo: R Morini
In its publication No Peat Potting Soil Options, the University of Minnesota Extension offers several mix recipes using coir. Key coir characteristics include:
- Holds moisture well
- Wets more easily than peat
- Drains well
- Decomposes more slowly than peat
- Resists compaction
- Less acidic than peat
- Low nutrient content and high cation exchange rate, that tends to hold on to stored nutrients, creating a need for nutrient additions from other ingredients and/or fertilizers.
- Also, when purchasing coir, check the label to be sure that it has been washed to remove salts. It appears that suppliers have added salt flushing washes to their processes, but it is worth confirming since salts can harm plant growth. If the salts haven’t been removed, the coir should be washed prior to use.
The Extension-recommended mixes, which are based on a blend of coconut coir and compost, include:
- For Seedlings
- 1 part compost
- 2 parts coconut coir
- 1 part builders’ sand
- For Ornamentals
- 1 part coconut coir
- 1 part compost
- 1 part top soil
- 1 part builders’ sand
- For Edibles
- 2 parts compost
- 2 parts coconut coir
- 1 part builders’ sand.
- Similar formulas using ground bark and wood materials are mentioned by other sources, although less commonly than coir.
In each case, additional fertilization is likely needed, and pH should be checked to match plant needs.
Are the mixes re-usable?
If last year’s potting soil had issues with disease, it should not be re-used in the garden. If it was basically weed- and disease-free, it is suggested that last year’s soil be removed from pots and mixed 50/50 with a fresh batch of potting mix prior to re-use.
Take-Aways
This brief run-through of possible substitutes for peat-based potting mixes indicates that there are lots of possibilities available, both commercially and home-made. Compost is a highly-valued component and is included in most options. Coconut coir seems to be the most favored peat substitute, although ground up wood products have some backers as a longer term solution that is less expensive and more sustainable than coir, which is imported from Asia and Central America.
Because of the variety of possible products and the importance of finding an effective solution, some professionals recommend taking a multi-year approach, experimenting with different mixes and a slow phase-out of peat, to offer the best odds of successful change with minimal disappointment.
In any case, I hope this discussion helps clarify possible solutions and helps environmentally-responsible gardeners make a successful change that supports our growing efforts while positively impacting the climate crisis.
SOURCES:
Featured Photo: Ralph Morini
“Coconut Coir vs Peat Moss,” Coconut-coir.pdf, Washington State Extension
Coir is sustainable alternative to peat moss in the garden | OSU Extension, Oregon State University Extension
Soilless Growing Mediums | okstate.edu, Oklahoma State University Extension
Growing Media (Potting Soil) for Containers | umd.edu, University of Maryland Extension
Peat-free potting mixes – Maryland Grows Blog / umd.edu, University of Maryland Extension
“No-Peat Potting Soil Options,” University of Minnesota Extension, Hennepin Master Gardeners
“COCONUT COIR AS AN ALTERNATIVE TO PEAT MEDIA FOR VEGETABLE TRANSPLANT PRODUCTION,” swfrec.ifas.ufl.edu, Southwest Florida Research and Education Center, University of Florida
Why Gardeners Should Stop Using Peat, and What to Use Instead – The New York Times (nytimes.com) (Margaret Roach, Feb. 6, 2022)
What’s Wrong with our Redbud?
Splotchy leaves on our redbud. Photo: CATHY CALDWELL
Like most folks, I’m particularly fond of redbuds, and I treasure several in our yard. Two are volunteers — the most welcome volunteers ever! — but one of those volunteers suddenly started looking unwell last summer. Its leaves were spotty, but not the familiar brown spots of fungi, such as Cercospora, which I’ve learned to take in stride. See Illinois Ext. Then the leaves began to turn brown way too early, and eventually, some branches appeared to be dead or dying. Research seemed to be in order; after some time on the computer, I began to worry that our redbud might have a serious disease that had only recently appeared on trees in the U.S. But there were a few other diseases that presented in a similar fashion, but none of them eased my mind at all.
Brown leaves, branches wilting and dying. Photo: CATHY CALDWELL
The most likely suspect was Botryosphaeria canker and dieback — a fungal disease to which redbuds are quite susceptible, especially if they’ve been stressed by drought. Symptoms of Botryosphaeria canker and dieback — which affects many species of trees and shrubs — are wilted or dead branches on a tree or shrub that looks healthy in other respects. My redbud does have a few branches that appear to be dead. Here’s what the experts at the Virginia Tech Plant Disease Clinic have to say about Botryosphaeria canker:
This is a common disease on redbud. Cankers are often centered at branch stubs or other wounds where the fungus gains entry. The fungus can also infect trees that have been weakened by drought, winter injury, or other environmental factors. No effective chemical control is available. Prune out affected branches. Make pruning cuts several inches below the cankered area, through healthy (white) wood. Pruning tools should be disinfested between cuts by dipping in alcohol or in a 10% solution of household bleach to prevent spread to the new wounds. Refer to the VCE factsheet on this disease for further information.
— Plant Problem Image Gallery, Va Tech Plant Disease Clinic
Botryosphaeria canker on redbud. Photo: Mary Ann Hansen, VA Tech Plant Disease Clinic.
How to protect your redbud from Botryosphaeria fungal infection? First of all, protect it from stress, and remember that any wound could be an entry point for the fungus. Do not prune when it’s wet; only when it’s dry. And if you’re pruning out diseased branches, follow the directions in this helpful video from Va Tech: www.youtube.VCE/Botryosphaeria Dieback – Common Plant Diseases in the Landscape and Garden. Also, if you’re planting a new redbud, be sure to provide its favored conditions.
If you think one of your trees or shrubs has Botryosphaeria — and I was beginning to suspect that’s what mine had — you’ll want to send a sample to the Plant Disease Clinic at Virginia Tech. It’s critical to provide them with a sample branch that contains both healthy and diseased tissue; i.e., a branch that contains a “junction of healthy (white) and diseased (brown to reddish-brown) tissue.” This type of sample is essential for diagnosis.
The next suspect on my list was Verticillium Wilt, another fungal disease that affects many trees and ornamental shrubs, and for which there is no cure. It can be caused by two different fungi, both of which reside in the soil, and sadly, can persist in the soil for a long time, infecting new plantings. The verticillium pathogen infects trees via roots and basically blocks the tree’s vascular system, preventing the transport of water and nutrients, leading to dieback and death. Just like Botryosphaeria, this disease is less likely to infect trees that have optimum growing conditions.
My redbud had the usual symptoms of verticillium wilt: “wilted, shriveled, scorched or browning leaves; off-color foliage; stunting; defoliation; dieback and death.” Verticillium Wilt of Shade Trees and Woody Ornamentals/VA Tech. Reading about verticillium wilt was a rather scary experience because my redbud is surrounded by much-loved perennials that could be infected. Even if the disease progression could be slowed by careful watering during summer’s dry periods, transplanting those perennials would simply spread the pathogen to a new area of the garden.
Verticillium wilt on cherry tree. Photo: H.J. Larsen, Bugwood.org
On top of the spreading-through-the-soil issue, there’s even a problem with removing an infected tree — which is recommended if most of the tree appears to be sick. The remains cannot be composted or chopped into mulch (also contagious) and must be landfilled — but not in an area where free mulch is being prepared! All of these contagion problems dictate that only resistant species be planted in areas where verticillium has been diagnosed. For a list of resistant or immune species, as well as a list of susceptible species, see Verticillium Wilt of Shade Trees and Woody Ornamentals. Verticillium wilts also affects a number of vegetable crops, though mostly in areas north of us. See Verticillium Wilt of Vegetables/Univ.Md.Ext.
Next on the list of suspects was Vascular Streak Dieback, a disease that appeared in parts of the United States in the past two years, and which had formerly been known only as a disease of cacao plants in Southeast Asia. In Virginia, it has been redbud, maple, and dogwood that have been apparent victims of vascular streak dieback (“VSD”). Scientists are scrambling to learn more about VSD, and so far have not been able to make a positive identification of the cause. Here’s a summary recently prepared by a group of Virginia Tech researchers:
In the past two years, nurseries in Virginia and some other states have observed wilt and severe dieback on redbud, maple, and dogwood stock (Beckerman et al. 2022). In some cases, 90-100% of stock was unsellable due to the extent of damage. Early symptoms include leaf chlorosis, scorched leaf margins, and stunting and/or wilting of current year’s growth, eventually leading to death of individual branches and progression into the main stem. Wilting typically starts on the top of the plant and progresses downwards into and along the main stem. Streaking or discoloration within the vascular, or water conducting, tissue occurs when symptomatic branches and/or main stems are cut. However, vascular symptoms may be subtle or absent on dogwood or other hosts, adding a challenge for diagnosis. Commonly, opportunistic fungi such as Botryosphaeria and Phomopsis colonize the weakened branches and cause cankers, adding another challenge for detection of the primary causal agent.
The fungus Ceratobasidium theobromae (synonym: Rhizoctonia theobromae) has been consistently associated with vascular tissue of nursery stock showing the symptoms described above. This fungus has previously been reported as the cause of vascular streak dieback (VSD) on cacao in Southeast Asia (Samuels et al. 2012). Therefore, plant pathologists in the United States are calling the putative disease VSD.
—Vascular Streak Dieback: An Emerging Problem on Woody Ornamentals in the U.S.
Scientists are advising that trees diagnosed with C. theobromae be removed and incinerated. They are also suggesting that healthy plants might be protected from infection through the use of systemic fungicide soil drenches that are labeled for management of Rhizoctonia. To learn more about VSD, you’ll want to read Vascular Streak Dieback: An Emerging Problem on Woody Ornamentals in the U.S., which also provides detailed guidance on how to take a sample for diagnosis by the Virginia Tech Plant Problem Clinic.
Vascular Streak Dieback on container redbuds. Photo: Devin Bily, VA Dept. of Agriculture & Consumer Services
After studying the three suspects and numerous photos of each disease, it became clear that professional help was needed. So, I followed the directions for taking samples of branches and soil and took them all to the Extension Office, where staffers mailed them to the Plant Disease Clinic at Virginia Tech. When an email from the Clinic landed in my inbox, I took some deep breaths and opened it. Which of the suspects was it? None of them! That’s right, dear reader. Our redbud was a victim of a problem I had not even considered: decay. The report very helpfully detailed the testing that had been done and concluded as follows:
The trunk of our ailing redbud. Photo: Cathy Caldwell
Based on the damage and appearance of the trunk in the photo submitted, I think there is very likely decay in the main trunk of this tree. Many different fungi cause wood decay. Most decay fungi enter through wounds (e.g. planting wounds, lawn mower, weed whacker, etc.) on stressed trees.
–Plant Specimen Diagnostic Report # 2023-248 Redbud
I was quite surprised by the report, but also relieved. Although our redbud will eventually succumb to the decay, the end will not be immediate. And I was relieved that nearby plants were not in danger of catching a case of verticillium wilt. Frankly, I learned a great deal from this experience. There are a lot of fungal diseases out there, but if you protect your trees and shrubs from stress, they will likely be able to avoid them. If you do spot a problem, take advantage of the diagnostic expertise available from the university serving your extension office. You’ll be glad you did!
SOURCES:
Featured Photo: Redbud believed to have vascular streak dieback by Nicole Kopas, Va. Department of Agriculture and Consumer Services
“Vascular Streak Dieback: An Emerging Problem on Woody Ornamentals in the U.S.,” VA Tech (Devin Bily, Plant Pathologist, Virginia Department of Agriculture and Consumer Services, and Elizabeth Bush, Extension Plant Pathologist, School of Plant and Environmental Sciences, Virginia Tech, 2024)
“Eastern Redbud Tree,” The Garden Shed
“Verticillium Wilt of Shade Trees,” Va.Coop.Ext/www.pubs.ext.vt.edu/450-619
www.youtube.VCE/Botryosphaeria Dieback – Common Plant Diseases in the Landscape and Garden
“Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape,” VaCooperativeExt./450-726
Upcoming Events
Invasive Plant Workshop at Rockfish Valley Trail in Nellysford
Friday, April 5 @ 10:00 am — 1:00 pm
Join Blue Ridge PRISM’s knowledgeable staff at the beautiful Rockfish Valley Trails to learn about invasive plant ID, herbicide safety, basic management strategies, and a step-by-step tutorial on how to use herbicide techniques as well as manual control options. This workshop will include an invasive plant identification walk on the Camille Trailhead, Rockfish Valley Trails, Nelson County.
Registration fee is $25. Register HERE
CATS 2024 Tree Sale: April 6 @ 10:00 am – 12:00 pm
Virginia Department of Forestry, 900 Natural Resources Drive, Charlottesville.
Identify and Control Non-Native Invasive Plants in Spring
Part 1: Introduction and Identification :
Zoom presentation: Tuesday, April 9 @ 7:00 to 9:00 p.m. ⇒ Register here
Part 2: Control Methods
Zoom presentation: Thursday, April 11 @ 7:00 to 9:00 p.m. ⇒ Register here
Tim Maywalt, Tree Steward and of the Blue Ridge Partnership for Regional Invasive Species Management (Blue Ridge PRISM) will present this two-part class by Zoom. We will cover:
Identifying invasive plants
Why fall/winter is a good time to control invasive plants
Planning your control program
Using manual & mechanical control methods
Choosing the right herbicide and equipment, and using it properly
Chemical control methods
Forest safety, equipment and herbicide safety, and personal protective equipment.
Reference documents for more detailed identification and treatment information.
Sources for equipment, supplies and professional help from State Foresters and Conservationists and commercial vendors
Guided Walk: Late Spring’s Glorious Forest Understory Plants
Saturday, April 13 @ 10:00 to 12:00 p.m. ⇒ Register here
Join Tree Steward guide and property owner Phil Stokes for this spring walk in a pristine remarkably diverse 30-acre mature woodland as trees, wildflowers, and ferns announce spring’s arrival.
See the wonders of many naturally occurring ephemeral blooming wildflowers such as wild geranium, star flowered chickweed, toothwort, rue anemone, and a variety of ferns on this easy 1 ½ mile walk along trails. In addition we’ll visit restored woodland understories thriving with planted trilliums, Jacob’s ladder, trout lily, Mayapple, Virginia bluebells, and various other wildflowers. Pinxter bloom azaleas indigenous
to the site should also be in bloom as well as serviceberry, maple, and paw paw.
Directions will be sent after registration is complete. Limited to 15 people. No restrooms available.
UVA Guided Tree Walk
Saturday, April 13 from 9:30 a.m. — 11:00 a.m. ⇒ Register here
Join Charlottesville Area Tree Stewards on this walk at the University of Virginia through beautiful surroundings and spring blooms as we discuss the history of the area, some specimen and native trees. We will share information about the value of biodiversity, tree identification, and specific qualities related to each tree discussed. This is an easy to moderate walk over a gentle sloping area of paved walkways and grassy areas under a high canopy of trees.
Blue Ridge PRISM’s 2024 Spring Meeting
“Native Plants for Your Landscape,” with Peggy Singlemann
Tuesday, April 16, 2024
11:30 am – 1:00 pm
(via Zoom)
REGISTER
Garden Basics: Native Plants for Shade
April 20 @ 2:00 pm – 4:00 pm
FREE
Adding native plants to your shady yard is both ecological and beautiful. Learn how to: layer your landscape, identify types of shade, and determine which plants work in each situation. We will cover trees, shrubs, and perennials.
Garden Basics is a partnership with the Bread and Roses ministry at Trinity Episcopal Church.
Space is limited. Please register below to reserve your place in the class. Registration closes at 5 p.m. April 19, 2024, or when the class is full.
Find out more and Register Here
Virginia Department of Forestry Callery Pear Tree Exchange: Remove and Replace your Callery Pear Trees
SATURDAY, APRIL 20:
Pre-registration required – view PDF with more information here.
The Virginia Department of Forestry (DOF) is rolling out a new exchange program to help slow the spread of Callery pears from the urban landscape into our natural areas. DOF’s new Callery Pear Exchange program incentivizes the removal of up to three (3) Callery pear trees from your property to receive an equal number of native, young, healthy – and free – replacement trees.
Coming up in May . . .
Piedmont Master Gardeners’ Spring Plant Sale
Saturday, May 4 @ 10 am – 2 pm.
The Piedmont Master Gardeners’ annual Spring Plant Sale will be held from 10 a.m. to 2 p.m. Saturday, May 4, at Albemarle Square Shopping Center in Charlottesville. The sale will offer thousands of annuals, perennials, vegetables, fruit-bearing plants, herbs and and houseplants, including a large assortment of native plants. In addition, shoppers can purchase garden implements, yard ornaments and other “Green Elephants.” The sale will happen rain or shine and will feature a Help Desk for answering gardening questions and educational displays on a variety of topics.
Garden Basics: Dividing Bulbs, Corms, Tubers, and Rhizomes
May 18 @ 2:00 pm – 4:00 pm
FREE
Many beautiful plants come from bulbs, corms, tubers, and rhizomes. Some can be left in the ground over the winter, while others can be dug up, stored, and planted the following spring. You will discover:
- how to identify bulbs, corms, tubers, and rhizomes;
- how they reproduce;
- how to dig them up; and
- how to store them for the winter.
A hands-on activity will demonstrate the proper method for dividing. Garden Basics is a partnership with the Bread and Roses ministry at Trinity Episcopal Church.
Space is limited. Please register below to reserve your place in the class. Registration closes at 5 p.m. May 17, 2024, or when the class is full.
April in the Edible Garden
It’s April and if you haven’t already planted outside, gambling on the warm winter weather we have had, now is a good time to get the edible gardening going. The air and ground are warming, buds are fattening and early planters may soon be enjoying some garden produce. If you haven’t gotten started yet, April is a great time to plant cool weather vegetables. Given the recently revised average last frost dates of April 5-15 in Hardiness Zone 7b, outdoor planting is definitely underway. However, given the crazy weather we have had, it is important to monitor the weather and be prepared to protect sensitive plants if an unexpected freeze comes along.
Bed Preparation
As mentioned in previous articles, deep tilling is no longer a recommended practice, except for new beds where loosening compacted soils and integrating organic matter can make sense.
Trimmed winter cover crop at UAC CATEC Garden. Photo: R Morini
If you grew a cover crop over the winter, let it grow as long as possible, ideally cutting it after flowering, prior to seed formation. Late cutting (photo above) enables deepest root penetration to loosen soil and greatest photosynthetic carbon deposits and since it has spent big energy to flower and start creating seeds, plants are too weak to regrow after cutting. To remove the crop, cut it as close to flush with the soil as possible, with a string trimmer or mower. The residue is best left in place as a mulch or removed and composted. Give the roots a couple of weeks to start decomposition and then plant. If you want a smoother seed bed or can’t wait long enough to remove the cover crops post flowering, use a stirrup hoe (some call it a scuffle hoe) to cut the crowns, just below soil level. Leave them as mulch or add to compost.
Photo from video: “The Broadfork”, Jean-Martin Fortier, The Market Gardener’s Toolkit,”
Occultation is a no-dig alternative for weed control. It involves covering beds with a black plastic tarp or landscape fabric for 4-6 weeks to starve weeds of sun and kill them with heat. Remove the tarp and plant transplants directly. If seeding, rake off residue and compost it while smoothing the planting row.
To loosen compacted soil, drive a digging fork or broadfork as deeply into the soil as possible and rock it back and forth to loosen soil without destroying structure. Work your way across the beds. If adding an amendment like compost or manure, layer it on top and allow it to work into the soil during broadforking. Rake the surface smooth, and you are ready to seed.
Planting
If starting from seed, follow packet directions. For intensive or square foot gardening, ignore the row spacings and use seed-to-seed spacing in both directions. Goal is to space plants so that mature plants will just touch each other, shading the soil to reduce moisture and weed pressure while maximizing production for a given space.
Fertilization is important for best results. For guidance on what products to use and how and when to apply them, review Garden Shed article A Fertilization Primer.
According to Virginia Cooperative Extension’s Virginia’s Home Garden Vegetable Planting Guide, in Hardiness Zone 7b (note that the map doesn’t reflect the change of our region from 7a to 7b but we can use the 7b planting date list).
There is still time to plant cool weather crops, including: beets, broccoli, cabbage family items, carrots, various greens, and lettuces, onions, potatoes and turnips. Mid-April is the suggested planting time for bush and pole beans, cucumbers, eggplant, melons, squash and tomatoes. However, these guys are harmed by frost, so check the longer-term weather forecast before setting them out or planting. Be prepared to protect them if a late frost arrives.
A Few Tips
- Where possible, rotate your crops, on a 3-4 year cycle to minimize pressure from soil borne diseases and pests.
- Maintain a journal to record planting dates, crop locations, varieties planted, pest and disease issues, and growing success. You will be thankful when you plant next year.
- Plant seeds at a depth of about 2 times the seed width (not length). Moisten when planting and keep moist until germination.
Trellis. Photo: U of Minnesota Extension
- Trellises area great way to save space and keep plants off the ground. VCE publication Vertical Gardening Using Trellises, Stakes and Cages offers guidance for a variety of space-saving plant supports.
Hardening-off seedlings. Photo: R Morini
- If you started seeds indoors, remember to harden the plants off by progressively exposing them to the outdoors for 1-2 weeks when outside temperatures are above 50 degrees, prior to transplanting.
- It is best to transplant on a cloudy day or in late afternoon to reduce shock to young plants. If transplanting peat pots, tear off the top of the pot to a point below the soil line to avoid wicking water away from plant roots.
- Mulching plants after transplanting or germination is a good thing but give the soil a chance to warm up before mulching to avoid slowing plant growth.
- When laying out plant locations, remember that leafy greens typically require 6 hours of sun per day while fruiting vegetables want at least 8 hours.
- Consider intercropping. Mixing different plant varieties uses space well, adds diversity to the garden environment, creates a variety of scents that can confuse pests, and attracts a broader array of beneficial predators, helping reduce pest damage.
Swiss Chard. Photo: Courtesy of Pixabay
- If you would like to extend the harvest season for your greens, consider chard. Chards have a lower tendency to bolt and can withstand summer heat longer than most other greens. In addition, rainbow chard makes a pretty presentation in the garden.
- Should a surprise late frost threaten your warm weather crops, a row cover can save the day. Review the Garden Shed article: Row Covers: A Garden Season Extender with Benefits for material and construction tips.
- It isn’t too late to plant asparagus or strawberry patches. For guidance on starting asparagus refer to the Garden Shed article Spear Into Spring with Asparagus, and the VCE publication Asparagus, which specifies recommended cultivars for Virginia. For strawberries try Garden Shed article Strawberry Basics for the Home Garden.
April strawberries. Photo: R Morini
- For small fruits more broadly, check out the VCE publication Small Fruit in the Home Garden.
- If you are planning a home orchard, check out the VCE publication Tree Fruit in the Home Garden for help in site selection, tree selection and care for many popular fruits.
- Best tree planting techniques for both bare root and root ball trees is detailed in Planting Trees Correctly from the Clemson Extension.
- If you are curious about the weeds in the garden or its surroundings, for elimination or edibility, VCE’s Weed Identification Guide is a good resource.
I hope you find this information helpful. Comments on content are welcome. In any case, enjoy your garden and please come back next month.
SOURCES:
Featured Photo: Winter cover crop at UAC Garden at CATEC: Photo: Ralph Morini
Virginia’s Home Garden Vegetable Planting Guide: Recommended Planting Dates and Amounts to Plant, Va.Coop.Ext.Pub. 426-331
April in the Ornamental Garden
April is prime planting season for gardeners in the mid-Atlantic. In fact, this can be our busiest month as we contend with spring cleanup, dividing, transplanting, weeding, and other spring gardening chores. The bright, sunny days and warm spring breezes this month are perfect for working outside and we can be lulled into thinking cold weather is behind us. But it’s important to stay vigilant for sudden dips in night-time temperatures that can result in deadly overnight frosts.
The average last spring frost in Albemarle County (USDA Zone 7b) generally occurs between April 15 and April 25. If a frost is forecast, cover tender new growth to protect it from frost damage. Use a row cover, an old sheet, cardboard, or even layers of newspaper for this purpose. Remove the coverings the next morning so that you don’t inadvertently “cook” your plants as daytime temperatures warm up.
As daffodils and hyacinths finish blooming, cut the flower stalks all the way back to the ground but leave the foliage in place to die back naturally. This allows the plant to focus on storing energy for next year’s blossoms rather than on developing seed heads. The foliage may look a bit messy, but don’t braid or tie it up because this may interfere with photosynthesis, which could affect next year’s blossoms.
If spring-flowering bulbs such as daffodils, snow drops, or crocus have become crowded and didn’t produce as many flowers as in past years, that may mean they need to be divided. The ideal time to divide these bulbs is after the foliage has died back, which may be June or July. Mark the location of the flower clump now while you can still see the green or yellowing foliage. This will help you remember where the clump is located, plus it will remind you not to plant something else in the same spot. Make a note to dig up and separate the bulbs once they are dormant. Either replant them immediately or store them in a cool, dry, well-ventilated place and replant them in the fall.
Top dress established ornamental flower beds with an inch of compost. For new flowerbeds, work compost or aged cow manure into the loosened soil before you start to plant. A slow-release fertilizer and lime may also be added to the soil if a soil test indicates the need for either.
Hairy bittercress. Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, CC BY 3.0
Remove broadleaf winter weeds before they set seed. These cool-season weeds include chickweed, deadnettle, hairy bittercress, and henbit. They germinate in late summer or early fall, overwinter in the landscape, and produce flowers and seeds in spring. You can suppress their growth in your flower beds by applying a layer of mulch over bare ground or planting a dense ground cover. Weed identification information and photos are available on a number of extension websites such as Virginia Tech (weedid.cals.vt.edu), University of Missouri (weedid.missouri.edu), or the University of Illinois (weeds.cropsci.illinois.edu).
Divide fall-blooming perennials, such as asters (Symphyotrichumspecies), chrysanthemums (Dendranthema), shasta daisies (Leucanthemum), black-eyed Susan (Rudbeckia), ornamental grasses, sneezeweed (Helenium), false aster (Boltonia), and bee balm (Monarda). Most perennials benefit from being divided every three to five years on average, but if you’re not sure if a plant should be divided, here are a few questions to ask yourself:
- Is the plant not producing as many flowers as in previous years?
- Has it outgrown its assigned space in your landscape and is it crowding other nearby plants?
- Is it alive around the edges of the crown but dead in the center?
- Does it seem less vigorous in general?
- Do the stems in the center of the plant have smaller leaves?
- Are the inner flower stalks weak or flopping over?
If the answer to any of these questions is yes, then the plant probably needs to be divided. Try to complete this task at least six weeks before hot weather sets in so that the divisions have ample opportunity to become well established.
Another reason to divide perennials is to increase air circulation, which helps control fungal diseases. For example, Monarda fistulosa (or wild bergamot) is valued for its highly aromatic flowers that attract pollinator insects such as bees and butterflies, but it is subject to powdery mildew. By dividing this popular native plant every 3 years to improve air flow and providing it with moist, well-drained soil, a sunny site, and destroying all infected foliage, can help keep this common fungal problem under control.
Before digging holes for new plantings, keep in mind the ultimate size of each plant. Also, group plants together according to similar needs for water, nutrients, and sunlight. Remember to update your gardening records indicating the location of your new plantings.
Pinch back chrysanthemum foliage this month when the plants are about 4 inches high. Pinching makes the plant bushier, sturdier, and more wind-resistant later in the season. Tall aster species also benefit from being pinched back for the same reasons. False sunflower (Heliopsis helianthoides) is another plant that benefits from being pinched back in spring to reduce the plant’s height.
At this time of year, garden centers are overflowing with the best selections of landscape plants. Shop for azaleas and rhododendrons while they are in bloom to ensure you like the color and that the color harmonizes with your other landscape choices. This is particularly important if you are adding new plantings to an established landscape. Some pink selections, for example, have an orange or coral undertone that may clash with other spring-blooming species located nearby. Tip: Azaleas generally look best planted as a grouping in part sun or filtered shade and acidic, well drained, organically rich soil with a pH of 5.0 to 6.0.
As you select new plantings for your garden, avoid plant species that are potentially invasive in this area of Virginia. Look for native plants that minimize maintenance, require less water, and increase habitat, particularly for beneficial insects. A number of excellent native plant resources are available, such as the Virginia Native Plant Society’s website at vnps.org, the Albemarle County Recommended Native Plants website at webapps.albemarle.org/nativeplants, or the Virginia Department of Conservation and Recreation’s Natural Heritage Program at dcr.virginia.gov/natural-heritage. Also, explore back issues of The Garden Shed for a number of articles on native plants suitable for our area.
Buy annual bedding plants such as begonias, petunias, pentas, geraniums, or marigolds while selections are plentiful. Choose healthy plants with well-developed root systems that are not too large for their pots. Don’t plant them, however, until the danger of frost is past, night-time temperatures are consistently above 50° F, and soil temperatures are above 60° F. Depending on the weather, that may be toward the end of April or even early May. If you just can’t wait that long, be prepared to protect those tender seedlings from frost if temperatures threaten to turn chilly.
If you prefer to start bedding plants indoors from seed rather than buy transplants from a garden center, you can still sow the seeds during the early part of April if you didn’t get around to it in March. Don’t forget to harden off tender seedlings before planting them outdoors. For the new or inexperienced gardener, Virginia Cooperative Extension (VCE) Publication 426-001, Plant Propagation From Seed, provides good information on sowing seeds.
Plant some everlastings in your ornamental garden this spring. The term “everlasting” refers to a flower, seedpod, or other plant part that can be dried or preserved without the loss of its shape or color. Everlastings are used in dried flower arrangements, wreaths, bridal bouquets, and many craft projects. In addition to strawflower (Helichrysum), baby’s breath (Gypsophila paniculata), and statice (Limonium), all of which are easily preserved, try experimenting with other flowers such as: Bells of Ireland (Molucella laevis), cockscomb (Celosia), or globe amaranth (Gomphrena).
Don’t move your houseplants outside until night-time temperatures consistently stay at 50° F or higher. Depending on the weather, this may not happen until very late April or in May. Place them in a shaded area on a porch, patio, or under a tree or wherever they can gradually acclimate to the increased light levels. Moving a houseplant from indoors directly out into a sunny location can burn the leaves, which will severely damage the plant.
Before you move your houseplants outdoors for the summer, repot any that are rootbound. You can tell a plant is rootbound if:
- The roots are growing through the pot’s drainage hole or can be seen on the surface of the soil.
- The plant is either growing very slowly or has stopped growing even when fertilized.
- The lower leaves are turning yellow, which may be a sign of a nutrient deficiency.
- The potting mix is drying out faster requiring more frequent watering.
- The plant appears to be too large for the pot.
To repot a houseplant, choose a container that is only slightly larger in size. If the pot is too large, the soil can stay moist for too long, which can cause root rot. For additional information on houseplant care, see Virginia Cooperative Extension Publication 426-100, Indoor Plant Culture, or see the University of Maryland Extension’s publication on Potting and repotting Indoor Plants.
Boxwood leafminer damage. Photo: Jim Baker, North Carolina State University, Bugwood.org, CC BY-NC 3.0
With the arrival of spring comes the start of the annual battle with insects, such as leafminers. Leafminers are the larvae of insect species that burrow within a leaf and devour its inner layers, leaving either winding, serpentine tunnels or brownish blotches, depending on the plant and the leafminer insect species. Both the larvae and the damage they cause are generally undetectable until after it is too late. Winding tunnels caused by sawfly insects are commonly found on the foliage of columbine (Aquilegia), hollies (Ilex), and roses. The damage doesn’t actually harm the plant, but it can look unsightly. It’s usually sufficient to snip off the damaged leaves or simply ignore the problem if it’s not too pervasive. Other leafminer insect species cause blotchy or blistery-looking damage to plants such as boxwood. See University of Maryland Extension publication, Boxwood: Identify and Manage Common Problems for a description of and management options for boxwood leaf miners. To learn more about Leafmining Insects, see Colorado State University Extension Fact Sheet No. 5-548 and Boxwood Leafminers on Ornamental Plants/Univ. of Md..
Inspect Azaleas for lacebugs (Stephanitis pyrioides), which overwinter as eggs on the underside of infested leaves, then hatch out in spring. They damage foliage by piercing plant cells with their mouthparts and sucking the leaf dry. Look for white or silvery looking stippling on the upper leaf surface. The damage is unsightly, but it won’t kill the plant.
Slugs and snails start making their appearance in spring, particularly if the weather has been cool and wet. One very effective control method is to pick them by hand, or with tweezers if you’re squeamish, and drop them into a pail of soapy water to drown. For more information on how to control slugs and snails, see the University of Maryland extension’s publication on Slugs and Snails on Flowers.
Check emerging Irises for diseases or borer damage. Leaf Spot is one of the more common fungal diseases of irises. For information on symptoms and controls of this disease, see VCE Publication 450-600, Iris Leaf Spot. Iris borers are another common problem. The larvae of this pest feed below the soil level on the rhizomes. Feeding damage is sometimes not apparent until the plant dies or the leaves wilt. Inspect young iris foliage for notches that are cut in the edges of center foliage and slimy frass. This is the point where the borer enters the leaf. If you detect the presence of a borer caterpillar inside the leaf, crush it with your fingers. Once this voracious pest burrows to the rhizome, it will hollow it out and then proceed to other rhizomes. Bacterial soft rot often follows borer damage and can destroy an entire bed of Irises. The best way to control this pest is to burn the foliage or dispose of all dead or damaged leaves in the trash in fall.
And speaking of pests, apply deer repellent as vulnerable plants emerge in spring or take other preemptive measures to discourage deer browse on tender, succulent new plant growth.
Invasive Watch: Callery or Bradford (Pyrus calleryana ‘Bradford’) started blooming in March this year. This invasive species and other ornamental pears started out as popular landscape trees in the 1960s and are now considered invasive in 29 states. The trees often produce fertile seeds that are easily spread by birds. The seedlings can easily establish in disturbed areas, where they are contributing to the shrinking biodiversity of our urban forests. Control trees less than 6’ tall with a higher-than-usual (3-4%) concentration of foliar spray. Foliar sprays are effective from when leaves emerge in spring until just before they begin to develop fall color. For detailed information on how and when to eradicate this invasive species, including tree trunk methods in the fall, see the Blue Ridge Partnership for Regional Invasive Species Management’s Bradford Pear Fact Sheet.
Garlic mustard
Photo: Cathy Caldwell
Garlic mustard should be removed now before it flowers and sets seeds. For more about garlic mustard, see Blue Ridge Prism.org/Garlic Mustard Factsheet.
SOURCES
Feature photo of spring-blooming Phlox divaricata: Pat Chadwick