The Ornamental Garden in April
Two main activities, aside from compulsively running out to neighborhood nurseries to see what plants have arrived, capture the attention of gardeners in April — pruning ornamental shrubs and dividing perennial plants.
Before looking at these two activities, let’s consider other early-spring tasks that will help “set the stage” for a season-long ornamental display. At the threshold of the growing season, optimism runs high and digging in the dirt—even weeding—is a pleasure.
- Weed out the winter broadleaf weeds you missed in March. The University of Illinois Extension’s on-line publication on Weed Identification contains a number of useful close-up photos of weeds.
- Edge your beds and top-dress with a one-inch layer of compost, being careful not to disturb signs of emerging plants. After plants emerge a few inches more, add about 2 inches of mulch or ground leaves for weed control and moisture protection.
- Consider adding low-growing, native plants or sedges in bare areas where you ordinarily mulch, such as between shrubs in foundation plantings, or along paths.
- Identify spots where you’d like to add daffodils or other spring-blooming bulbs. Tent stakes work well as markers and can be a helpful physical aid to pictures.
- Sow seeds directly outside after checking planting directions on seed packets. For example, some seeds should not be planted until after the last frost; some can be planted 1-2 weeks before the last average frost date.
When is the average last frost date? Albemarle County and its surrounds are on the borders of the Piedmont and Mountain regions of Virginia. VCE (Virginia Cooperative Extension) Publication 426-331 puts Albemarle County in the Mountain region which has an average final frost date of May 10-15. On the other hand, USDA places Albemarle in Hardiness Zone 7a which specifies a final frost date of April 20-30. The University of VA Climatology Office is more in line with the April targets.
- For seeds started indoors, harden off seedlings before planting in open ground to prevent transplant shock. Place them in a shady location initially and bring them indoors at night if temperatures are predicted to drop below 50°F. For advice on transplanting seedlings, see the Virginia Cooperative Extension article, “Plant Propagation from Seed.”
- Remove faded flowers from daffodils, tulips and hyacinths, letting the foliage die naturally. Don’t braid or tie up the foliage since this could interfere with photosynthesis for food production. If your daffodils have become crowded and aren’t producing as many flowers as in past years, they need to be divided. Mark the location of the clump with a marker such as a golf tee, plastic knife, or wooden stick so that you can find it later in the summer after the foliage has died back. Make a note to dig up and separate the bulbs in July. (TIP: Use a different type of marker for dividing bulbs than you use for identifying empty spots you want to fill.)
- Prune hybrid roses when bud growth starts in early spring. When making cuts, prune back to just above an outward-facing bud. See the Clemson Cooperative Extension, “Pruning Roses.”
- Install stakes or ring-type supports for peonies.
- If a frost is forecast, protect tender new growth with row covers, old sheets, cardboard, or even layers of newspaper. Remove the coverings the next morning to prevent “cooking” your plants as the day warms up. Deutzia is one example of a spring-blooming shrub that will appreciate frost protection.
- Move your houseplants outside once night-time temperatures consistently stay at 50° F. or higher. Repot any root-bound plants into slightly larger pots. Fertilize with a slow-release fertilizer. Place the plants in a shady area initially so that they can gradually acclimate to being outside.
As a rule, shrubs that bloom in spring bloom on old wood and should be pruned after blooming. Many spring–flowering shrubs, such as azaleas, set next-year’s flower buds soon after they finish blooming in the current year. Therefore as a general rule, shrubs that flower before June 15 should be pruned soon after flowering. Examples of such spring-blooming plants are: azalea, deutzia (Deutzia gracilis), fothergilla (Fothergilla gardenia and F. major), Korean lilac (Syringa meyeri), Bridalwreath spirea (Spirea prunifolia).
Summer-to-fall-blooming shrubs bloom on new wood and should be pruned in late winter to early spring. This leaves plenty of time for the plant to recover from pruning and still create flower buds for the bloom season. Examples of these shrubs include: abellia, beautyberry (Callicarpa Americana), Hydrangea macrophylla (mophead), and Japanese spirea (Spirea japonica). In general, the time has now passed for pruning these shrubs. You can still prune dead wood or a few stray branches that are insulting your aesthetics, but resist full-scale pruning that will ruin this season’s blooms.
For more information on pruning, see The Garden Shed article, “When to Prune.” For a pruning schedule of specific shrubs, see the Virginia Cooperative Extension (VCE) publication, “A Guide to Successful Pruning, Shrub Pruning Calendar.”
Fortunately, there is also a general rule for plant division: divide late-summer or fall-blooming perennials in the spring, and divide spring/early summer bloomers in the fall. A sampling of plants that should be divided in spring includes:
- Blanket Flower (Gaillardia grandiflora)
- Canna lilies
- Lily of the Valley (Convallaria majalis)
- Most ornamental grasses
Some plants can be successfully divided in either spring or fall. A sampling of such perennials include:
- Beebalm (Monarda)
- Bellflower (Campanula)
- Cranesbill (Geranium)
- Garden Phlox (Phlox paniculata)
- Lamb’s ears (Stachys byzantina)
- Purple Coneflower (Echinacea)
- Red hot poker (Kniphofia)
- Black-eyed Susan (Rudbeckia fulgida)
- Tickseed (Coreopsis)
- Yarrow (Achillea)
For a list of when specific perennials should be divided, see the Virginia Cooperative Extension article, “Dividing Perennials.” This publication also includes a list of plants that should NOT be divided.
LAWN CARE SPRING QUICK TIPS
- Soil test before applying fertilizer. A soil test is the only way to determine if the soil needs lime, phosphorus (P) or potassium (K). Apply nutrients as recommended by a soil test and you’ll be taking a huge first step towards protecting water quality. See the April 2015 issue of The Garden Shed for an article on “Soil Testing.”
- Mow the lawn after it has grown at least two inches. The roots are being renewed in the spring and grass needs vigorous top growth initially. Set lawn mowers at the highest height early in the season.
- Topdress low spots and finish overseeding thin or bare patches.
- Apply crabgrass preventer before April 15. Do not apply to areas that will be seeded.
- Aerate turf if soil is compacted.
For a list of VCE publications on lawn care, including fertilization schedules, weed control, seeding, and overseeding, see VCE Tags.
INVASIVE SPOTLIGHT: WINEBERRY
Although not on the Terrible Twelve list of invasives identified by Blue Ridge PRISM (Partnership for Regional Invasive Species Management), this month’s invasive spotlight is on wineberry (Rubus phoenicolasius), another nonnative invasive in our area (and a scourge in my home landscape, in particular). Early spring is an effective time to begin a wineberry eradication project, especially when the soil is moist.
A member of the family Roseacea, the plant was introduced into the United States from Asia in 1890 as breeding stock for Rubus (blackberry and raspberry) cultivars and is still used today by berry breeders. Wineberry has a wide range of tolerance for light, soil type, and moisture level, and is hardy to USDA Zone 5 (annual minimum temperatures to -20 ºF). It is considered invasive in Maryland, Pennsylvania, Tennessee, Virginia, North Carolina, West Virginia, and the District of Columbia. It is listed as a prohibited invasive in NY.
The entire plant is covered in tiny, reddish hairs and sharp spines. The compound leaves are made up of three heart-shaped, toothed leaflets. The leaves alternate along the stem and are green on top, white on the underside. The plant grows in long shoots called canes up to 9’ long, which can re-root at the tips when they touch the ground. Wineberries are perennial; while the canes each live two years, the plant produces new canes every year. Leaves are produced in April; white, five-petaled flowers bloom in May; and red raspberry-like fruit appears from late June to August. The glandular-hairy calyx lobes envelop the developing fruits and keep them covered until almost ripe. Leaves drop in late November. Although its berries are a source of food for wildlife, wineberry’s rapid growth poses a threat to native plants by creating dense patches that crowd out desirable species. Its rapid spread creates spiny, impenetrable thickets that reduce an area’s value for wildlife habitat and for recreation.
This nonnative invasive reproduces clonally from root nodes, tip-rooting, and by seeds dispersed by birds, reptiles, and mammals. Wineberry is difficult to control and should never be deliberately planted. Small infestations can be handled by pulling individual plants—if the soil is moist and workable—or by digging them out with a shovel or spading fork. Where accessible, canes can be mowed with brush-type equipment. You can also cut the canes close to the ground and treat the open cut with an herbicide. In all likelihood, removal practices will need to be repeated. As with the treatment of any invasive, try to attack the invader before it becomes entrenched.
New York Invasive Species Information: Wineberry, http://nyis.info/invasive_species/wineberry/
USDA Fire Effects Information System, Rubus Phoenicolasius, https://www.fs.fed.us/database/feis/plants/shrub/rubpho/all.html
Wine raspberry, Invasive Plant Atlas, https://www.invasiveplantatlas.org/subject.html?sub=3072
Blue Ridge PRISM, https://blueridgeprism.org/