April Tasks in the Ornamental Garden
GENERAL APRIL CHORES IN THE ORNAMENTAL GARDEN
Top-dress established ornamental beds with an inch of compost and work it lightly into the soil. Do this every year and you’ll replenish the nutrients needed by your plants, plus improve your soil’s structure and water-holding capacity. This is probably the most important thing you can do to help your plants thrive and flower abundantly.
Clean up flower beds and borders, if you haven’t already done so. Cut back dead stems and foliage from perennials that were left standing over the winter. Check your shrubs for dried leaves that may have accumulated inside and under them; remove those leaves before the plant starts making its new leaves.
Re-edge flower beds and borders with a sharp-edged spade or half-moon edger, removing any grass or weeds that have migrated into them. Clarifying the boundary between lawn and flower bed is one of the best ways to give your ornamental garden a neat look.
Your beds may have winter annual weeds — broadleaf weeds like hairy bittercress, chickweed, deadnettle, and henbit — which reproduce by seed that germinates in fall, grows during the winter, and then produces flowers and seed in the spring. If you didn’t get them in March, be sure to root them out now, before they set seed. Then add a layer of mulch, which will suppress germination and growth of these weeds next year.
For photos and helpful identification tips for these and other weeds, check out the Virginia Tech Weed ID site. The University of Illinois Extension’s on-line publication on Weed Identification contains a number of useful close-up photos of weeds. While poking around in the Virginia Tech Weed ID site, I discovered that there are several kinds of chickweed.
Assess perennials that may need dividing, and for advice on making this decision, see last month’s article, Guidelines for Dividing Perennials. Some perennials can be divided in either spring or fall, but the general rule is to divide fall-blooming perennials in early to mid-spring. On the subject of when to divide, you can check this list before you proceed: When and How to Divide Some Common Perennials/Va.Coop.Ext..
Stay attuned to the weather and protect any ornamental plants that might be vulnerable to a sudden dip in overnight temperatures. You don’t want a freeze to kill the buds on your favorite flowering shrub. A row cover, old sheet, cardboard, or thick layer of newspapers will generally do the job. Our expected last frost date is now April 15–25 for Zone 7a, but “Expect the unexpected” is the watchword nowadays, thanks to climate change. Keeping up with the weather forecast is more important than ever.
TASKS RELATED TO PARTICULAR PLANTS
Trim back tattered or freeze-damaged Helleborus foliage in early spring. The current season’s flowers emerge from the center of the plant and are more appealing without the distraction of the old foliage. Epimedium, heuchera, heucherella, tiarella, liriope, bergenia and some ferns are other perennials with evergreen or semi-evergreen foliage that may need to be cut back or neatened up in early spring. Be careful not to snip new, emerging basal foliage or flower stalks by accident.
Divide fall-blooming perennials in early to mid-spring. Wait until later in the summer (July) to divide irises and Oriental poppies, and until autumn to divide daylilies and peonies. If you’re new to dividing plants, be sure to consult the recent Garden Shed article, Guidelines for Dividing Perennials.
Prune hybrid roses when bud growth starts in early spring. Before making the first cut, look at the overall architecture of the plant. Specifically look for and remove dead wood, the smaller or weaker of two crossing branches, thin (smaller than the diameter of a pencil) branches, interior facing branches, and inward facing buds. When making cuts, prune back to just above an outward-facing bud. As you make your cuts, look for any branches that have a hole in them, signaling cane borer damage. The interior wood surrounding the hole will usually be brown or tan. Cut the branch back until you reach white wood. As you prune, clean up any leaves or other debris from around the base of the shrub.
Install stakes or ring-type supports for peonies and train the foliage inside the ring. Peonies have a tendency to grow several inches practically overnight. It’s much easier to deal with the foliage when it’s only a few inches tall.
- Let the foliage die naturally. Green leaves produce food for plant growth next year. After leaves turn yellow, cut and remove the stems and foliage of the plants. Don’t braid or tie up the foliage since this could interfere with photosynthesis and reduce flowering next year.
- If you have overcrowded clumps of daffodils, they should NOT be divided until after the foliage has died back later in the summer, usually 6 – 8 weeks after they finish blooming. Bulbs dug and moved before foliage fades may not bloom for several years. Mark the location of the clump with a golf tee, plastic knife, or a tent stake.
Pruning Chores: Several early spring-blooming shrubs are ready for pruning in April, after bloom is done: forsythia (Forsythia x intermedia), winter jasmine (Jasminum nudiflorum), flowering quince (Chaenomeles japonica), pussy willow (Salix discolor), and witchhazel (Hamamelis vernalis). Fall-blooming witchhazel (Hamamelis virginiana) is also pruned in early spring. On these shrubs, flowers are produced on wood from past season, and begin setting buds for flowering next year soon after blooming. Before you start cutting, be sure to read A Pruning Primer: Tools, Techniques, and Timing in the February 2020 issue of The Garden Shed.
April is the ideal time to prune boxwood and cherry laurel. For a listing of other shrubs that can be pruned in spring, take a look at the helpful Shrub Pruning Calendar published by the Virginia Cooperative Extension, Va.Coop.Ext. Pub.No. 430-462.
EARLY SPRING PLANTING TIPS
Early in the month, plant cool-season annuals that can tolerate a light frost. Pansies, of course, are the quintessential cool-season annual, but there are lots of other choices for early spring. For example, calendulas, larkspur, love-in-a-mist, sweet alyssum and sweet peas all may be direct sown in the garden now. Some cool-season annuals that are best started indoors for transplanting after the last frost date include: forget-me-nots, lobelia, painted tongue, and snapdragons. Don’t forget to harden off the seedlings before planting them outside. For detailed instructions on this, check out a recent Garden Shed article, How to Start Your Garden Seeds.
As a general rule, late-summer or fall-flowering perennials are planted in spring, but check guidelines specific to each plant.
MONITOR FOR PESTS AND DISEASES
Be sure to monitor all that newly-emerging foliage for diseases and pests. The sooner you catch a problem, the less likely it is that major damage will occur. Also, take photos and start researching possible causes. Early efforts lessen the likelihood that drastic (as in chemical) treatments will become necessary. For a photo-based guide to identifying diseases of shrubs, see Shrub Diseases, Univ.Md.Ext..
Keep an eye out for the tiny boxwood leafminer fly, which has usually been seen buzzing around boxwoods in April as it prepares to deposit eggs in the leaves. It’s the larval stage that causes damage as it feeds between the upper and lower layers of leaves. If you see blisters on boxwood leaves, prune off the blistered foliage before the adult flies emerge. Dispose of the foliage in the garbage. Alternatively, you can break open a blistered leaf with a finger nail and remove the larvae. For more about the boxwood leafminer and other insect pests of boxwoods, look at Va.Coop.Ext.Insect & Mite Pests of Boxwood.
It has apparently not reached our area yet, but keep an eye out for spotted langernfly, which is a relatively new pest with the potential to do serious damage to a number of crops as well as home gardens. The Virginia Department of Agriculture and Consumer Services (VDACS) is endeavoring to prevent spread beyond Winchester and Frederick County, where it was originally identified in 2018. The VDACS just recently announced that this pest has become established in Clarke and Warren counties. One sign of possible infestation on a tree is sugary secretions called honeydew, which may then be infected with black sooty mold. For photos of each life stage of this insect and more information, including how to report a sighting, see Spotted Lanternfly in Virginia/ Va.Coop.Ext., Spotted Lanternfly Life Cycle in Virginia/Va.Coop.Ext. and Pest Alert: Spotted Lanternfly Va.Coop.Ext..
Eastern tent caterpillars (Malacosoma americana) overwinter as eggs, and the young larvae hatch around the time of bud break in March or April. The young larvae gather near the fork of the tree limb to begin spinning their web or tent. They emerge from the web to munch on leaves, but return to the “tent” at night. Eastern tent caterpillars are primarily found on native black cherry, crabapple, and apple trees.
Manual methods for removal of the tents are usually sufficient, but burning is not recommended. If you’re seeing a lot of tent caterpillars, remember that their egg masses, which are shiny and found on small twigs, can be removed in fall and winter. Natural controls include predaceous and parasitic insects (especially wasps), and disease organisms. They are a favorite food of the yellow-billed and the black-billed cuckoo. Trees usually recover from lost foliage unless the tree is young or weakened and stressed from other problems. If it appears that an insecticide is necessary, Bacillus thuringiensis (Bt, Dipel or Thuricide) is a safe biological spray. Trees usually recover from lost foliage unless the tree is young or weakened and stressed from other problems. Don’t be alarmed if you see mature caterpillars crawling on plants, walkways, buildings and the like. Mature migrating larvae are no longer feeding, but are seeking a place to pupate. Crushing them will probably decrease the population to some extent.
Don’t Forget the Deer Repellent
Deer tend to browse on broad-leaf evergreens as well as twigs and buds during the winter and early spring, so keep spraying your vulnerable plants with deer repellent. Keep monitoring for deer damage and change repellents regularly. And once that spring growth appears, start spraying it immediately. Your other option is to set up protective barriers, like netting. If you have comments or questions about either method, please write them in the comments section below. We’d love to hear from you.
Don’t Forget to Check out the Monthly Gardening Tips, now located under Gardening Resources on the main page of the PMG website: https://piedmontmastergardeners.org/gardening-questions/monthly-gardening-tips/#April
For more on April Tasks and Tips, consult previous issues of The Garden Shed:
Eastern Tent Caterpillar, Virginia Cooperative Extension (VCE), https://www.pubs.ext.vt.edu/444/444-274/444-274.html
Perennials: Culture, Maintenance and Propagation, VCE, https://www.pubs.ext.vt.edu/426/426-203/426-203.html
“Eastern Tent Caterpillar,” Entomology at the University of Kentucky, https://entomology.ca.uky.edu/ef423