Tasks and Tips in the Ornamental Garden
For many ornamental gardeners in our area, June is a maintenance month. Plants have been selected and planted, the temperatures are climbing steadily, and now we need to weed, pinch back, deadhead, water, and monitor for pests and diseases.
Just a reminder: The Piedmont Master Gardeners website has a new feature: monthly gardening tasks and tips are now appearing under Gardening Resources on the main page of the PMG website. For more June tips and tasks, take a look at Gardening Resources/Monthly Gardening Tips/Piedmont Master Gardeners
Don’t cut back daffodils until the foliage turns yellow or just let the foliage die back. Bulbs store food through the foliage for about 6 weeks after blooming is finished. Note that not all daffodils will turn yellow at the same time. The foliage of earlier bloomers will be ready for cutting before mid-to-late bloomers. If your daffodils were done flowering in mid-April, they should turn yellow by early June.
June is the time to divide crowded clumps of daffodils that aren’t producing as many flowers. When the leaves have turned almost all brown, carefully dig up the bulbs and separate them. Either replant them right away or store them until fall and plant then. Remember to take a picture of your daffodil plantings, or place a physical marker where you plan to add more bulbs in the fall.
Many perennials benefit from deadheading, which is removing seed heads after flowering is finished to allow the plant to store more energy for next year’s bloom. As soon as plants are allowed to set seed, chemical messages are sent to stop flower production. Removing spent blooms short-circuits this message so that the flowers will continue to bloom.
Flowers with larger blooms can be deadheaded by cutting one spent flower at a time. Such flowers include peonies, daffodils, roses, and zinnias. Another technique is shearing across the top of a plant that has many small blooms. This technique can be used in June-July for either pre- or post-bloom management. Early bloomers such as catmint (Nepeta), mountain bluet (Centaurea montana), bellflowers (Campanula) can be sheared by about one-third after blooming to encourage a second bloom and to neaten the plant’s appearance. Later-blooming plants with small flowers, such as sneezeweed (Hellenium autumnale), can be sheared by about 6-8” before blooming to encourage strong branching and denser growth.
There is another deadheading technique for plants that have flower spikes that rise from basal foliage (leaves immediately above the crown of the plant). Salvia nemorosa ‘May Night’ is an example of a plant with 6-10″ flower spikes that rise on short stems from rosettes of dark green basal foliage. Lance-shaped leaves are arranged in pairs directly across from each other. The small individual flowers on “May Night” spikes open from the bottom of the spike up. As the flowers at the tip fade, but before they set seed, snip individual stems away just above a pair of leaves that has small flower buds emerging from the joint. Cut between where the leaves emerge from the stem and the stem itself. Lateral branches will grow to produce new, smaller flower spikes. As the season goes on, the foliage tends to get very large and spent-looking. At this point, trim the stems back several leaf notches, or trim stems all the way to the basal rosette. Pale beardtongue (Penstemon pallidus) is another example of a plant with basal rosette leaves.
Late-bloomers, such as asters, chrysanthemums, and sedums, can be pinched back until mid-July to encourage a fuller, sturdier shape. This term means that you literally pinch out the growing tip of each stem between your thumb and forefinger. Pinching back will delay blooming somewhat, but the fuller plant shape and stronger stems are worth the wait. The technique also helps you tweak bloom times. If you have a big grouping of asters, for example, you might pinch one group a little earlier and more frequently than others so that the bloom season is extended overall.
Lungwort (Pulmonaria) is a beautiful, low-growing, early-spring blooming perennial that likes a moist place in the shade garden. In mid-summer, remove the flower stalks to stop seed production and to give more energy to the plant. When the foliage starts to turn yellow, trim off the spent leaves down to the base. This makes the foliage healthier and neater, especially when it has been damaged by slugs. Brunnera macrophylla is another spring-blooming shade plant whose leaves can get brown and damaged by slugs. Remove the oldest, yellowest leaves down to the base. Although neither of these plants rebloom, they will look fresher with new foliage.
June is prime time for pruning some shrubs. Check the Virginia Cooperative Extension (Va. Coop. Ext) Publication 430-462, “Shrub Pruning Calendar” for information on which shrubs to prune in June and which shrubs not to prune in June.
Annuals and Perennials
As June temperatures rise, keep an eye on watering, especially for newly-added perennials and annuals. Remember that plants will dry out even more quickly on windy days. The general rule of thumb is one inch of water per week for established plantings. Watering plants more deeply but less frequently encourages them to set deeper roots; this helps plants become more drought resistant. Mulch perennials with a 2-inch layer of compost, pine bark, or pine straw to help keep down weeds and conserve moisture. Avoid overly heavy mulching that could cause crown rot.
As the summer continues, container plants need more water. More water evaporates in the heat, and the plants grow larger. Depending on the size of the pot and the types of flowers, you may need to water twice a day, once in the morning and again at the end of the day. When choosing plant groupings for containers, be mindful of water requirements. Group plants that require moist conditions in one container, and group drought-resistant plants in another container. Water the plants until the water comes out of the drainage holes. Water the soil, not the leaves and flowers. Wet foliage can lead to fungal diseases or to scorched spots on leaves. Water-soluble liquid fertilizer should be applied approximately every two weeks. For more information on caring for container plants, see The Garden Shed.
Newly Planted Trees and Shrubs
Newly-planted shrubs are considered established when their root spread equals the spread of the above-ground canopy. This usually takes between 1-2 years. For trees, establishment is estimated by allowing 1.5 years per inch of tree caliper. Therefore, a 2” caliper tree will take about 3 years to establish on average.
How much water is enough? This answer depends partly on how much water the soil retains. Assuming well-draining soil, these recommendations are provided by the University of Minnesota Extension:
- 1-2 weeks after planting, water daily.
- 3-12 weeks after planting, water every 2 to 3 days.
- After 12 weeks, water weekly until roots are established.
- When watering newly-planted trees, apply 1-1.5 gallons per inch of stem caliper at each watering.
- When watering newly planted shrubs, apply a volume of water that is 1/4 – 1/3 of the volume of the container that the shrub was purchased in.
Place 2-3” mulch around the base of the tree AWAY FROM THE TRUNK. Too much moisture build-up between the trunk and the mulch can cause wood decay diseases, and fungus infections.
LOW MAINTENANCE PERENNIAL GARDEN
There are lots of maintenance tasks in the June garden, which brings us to the larger question, “Is there such a thing as a low-maintenance perennial garden? The Chicago Botanic Garden offers some tips:
Give careful consideration to plant choice and plant location. Matching the requirements of a plant to the characteristics of the site takes some planning, but will save hours of work in the garden. Soil and water conditions are important things to consider. Here is an example from my own garden:
Sedge (Carex) is a groundcover that attracts butterflies and is a good native alternative to Liriope. I chose Carex flaccosperma which has a beautiful bluish tinge and foliage that’s a little broader than some of the other sedges. C. flaccosperma requires moisture and a shady location. My planting was along a main path, near a water source. But did I want to spend all that time watering for a less-than-optimal result? The beautiful, bluish green color faded to yellowish-green. The planting location is too sunny and too dry; I’ll need to find a shadier spot for growing this sedge. For more information on Carex, see The Garden Shed.
Some plants are aggressive spreaders, perhaps too aggressive for a low-maintenance gardener. An example from my garden involved mist flower, Conoclinium coelestinum, a native perennial that spreads through both creeping rhizomes and through self-seeding. The seed is both abundant and wind-carried. The perennial has a beautiful blue-colored flower that looks very similar to annual ageratum, and blooms profusely from mid-to-late summer. I was very happy with it the first season, but a little less so the second. By the third season I was spending way too much time pulling out little starter plants. Although they come out easily, it was very time consuming to keep the spread under control. I finally decided to pull out all of the mist flower, giving some away with “fair warning” to other gardeners. For another gardener, with a different type of landscape, the spreading qualities of this plant might work very well. For more information on this plant see The Garden Shed.
If you want the garden to look pristine, you have to deadhead and groom weekly. On the other hand, a looser, more naturalistic look, requires less maintenance. Most plants will benefit from deadheading for continued bloom, but you can choose whether or not to take on this chore. Many native plants can look very attractive with spent seed.
Some plants to consider that do not require deadheading include: Astilbe, blue false indigo (Baptisia australis), Russian sage (Salvia yangii, previously known as Perovskia atriplicifolia), Blue star (Amsonia tabernaemontana), Blue star (Amsonia hubrichtii), various ornamental grasses, and sedge. For reduced maintenance, you might also wish to avoid plants that require labor-intensive division such as irises and lilies.
MONITOR FOR MILDEWS
Ornamental plants are subject to two common types of mildew that will manifest early in the season, around June 1, depending on conditions. Powdery mildew is a true fungal pathogen that produces white, flour-like colonies, usually on upper leaves. The fungus can cause severe leaf drop, and affects vigor and resistance to stress over time. The fungus can affect many ornamental plants that are favorites in the perennial garden, including: wild bergamot (Monarda fistulosa), bee balm (Monarda didyma), garden phlox (phlox paniculata), tickseed (Coreopsis grandiflora), purple coneflower (Echinacea purpureum), and zinnia.
Downy mildews, on the other hand, are a completely different kingdom of organisms, more closely related to algae than to fungi. Downy mildews produce grayish, fuzzy looking spores and mycelium on the lower leaf surfaces. The distinction between powdery mildews and downy mildews is important, because the fungicides effective against one are not usually effective against the other — although, as with every rule, exceptions do exist.
Preventative controls for each disease are important and include the following steps: selecting disease-resistant varieties and cultivars, providing good air circulation among plantings, and disposing of diseased foliage. The early use of fungicides may be necessary. Different fungicides are effective for each disease. See powdery mildew and downy mildew.
Japanese beetles begin appearing in June with adult activity often peaking in early July. Adult Japanese beetles are mainly leaf feeders that consume the tissue between leaf veins. Because the veins of the leaf are left intact, the damage is often referred to as skeletonization. Handpicking is an early deterrent. See The Garden Shed for sources on treatment.
Azalea Lace Bug and Rhododendron Lace Bug both have two generations per year. Please note: Lace bugs should not be confused with the beneficial lacewing insects that have long wings held vertically against their sides, Lace Bugs, Univ. Conn. Ext.. ( If you haven’t done so already, read about those beneficial lacewings in this month’s feature article, Natural Pest Control/The Garden Shed.) Lace bug damage is first noticed as yellow spots on the upper leaf surfaces of affected plants. Lace bugs actually feed on the undersides of leaves with their piercing-sucking mouthparts. When feeding damage becomes severe, the leaves take on a gray, blotched appearance or can turn completely brown. As lace bugs feed, they produce brown varnish-like droppings that spot the underside of the leaves. Try to control the first generation from mid-May to mid-June; two sprays may be necessary. Sycamore Lace Bug should also be treated in June or when nymphs appear. Multiple generations occur each year and defoliation may occur in severe cases. For control measures, see this link from the University of Georgia Extension.
Aphids can attack shrubs, trees, perennials, and annuals. Catching the infestation early is key. For information on identification and treatment see this link from Virginia Cooperative Extension.
Check for ticks whenever you spend time out in the garden. See “Managing the Tick Problem” from The Garden Shed.
The Piedmont Master Gardeners website has a new feature: monthly gardening tasks and tips are now appearing under Gardening Resources on the main page of the PMG website. For more June tips, take a look at Gardening Resources/Monthly Gardening Tips/Piedmont Master Gardeners
“Maintaining a Perennial Garden,” Chicago Botanic Garden, https://www.chicagobotanic.org/plantinfo/maintaining_perennial_garden
“Watering Newly Planted Trees and Shrubs,” University of Minnesota Extension, https://extension.umn.edu/planting-and-growing-guides/watering-newly-planted-trees-and-shrubs
“Daffodil FAQs,” The American Daffodil Society, https://daffodilusa.org/daffodil-info/daffodil-faqs/
“How and When to Prune a May Night Sage Plant,” SFGates, https://homeguides.sfgate.com/prune-may-night-sage-plant-40509.html
“Shrub Pruning Calendar, Virginia Cooperative Extension, pubs.ext.vt.edu/430/430-462
“Successful Container Gardens,” University of Illinois Extension, https://web.extension.illinois.edu/containergardening/fertilizing.cfm
“Container Gardening II: What to Grow & How,” The Garden Shed, https://piedmontmastergardeners.org/article/container-gardening-part-2-what-to-grow/
“Powdery Mildew on Phlox and Monarda,” University of Vermont Extension System, Leonard P. Perry, https://www.uvm.edu/~pass/perry/cohmild.html
“Downy Mildew,” Purdue Extension, https://www.extension.purdue.edu/extmedia/BP/BP-68-W.pdf
“Fungal Disease: Powdery Mildew,” University of Illinois Extension, hortanswers, https://web.extension.illinois.edu/hortanswers/detailProblem.cfm?PathogenID=147
Japanese Beetles, West Virginia Extension Service, https://extension.wvu.edu/lawn-gardening-pests/pests/japanese-beetle
Lace Bugs, Virginia Tech Cooperative Extension, Eric Day, Publication 444-212. https://www.sites.ext.vt.edu/departments/entomology/factsheets/lacebug.html
Control of Lace Bugs on Ornamental Plants, University of Georgia Extension, https://extension.uga.edu/publications/detail.html?number=B1102&title=Control%20of%20Lace%20Bugs%20on%20Ornamental%20Plants
Aphids, Virginia Cooperative Extension, https://www.pubs.ext.vt.edu/444/444-220/444-220.html
“Managing the Tick Problem,” The Garden Shed, https://piedmontmastergardeners.org/article/managing-the-tick-problem/
Feature photo, Monarda didyma, Andrey Korzun, Wikimedia Commons