The Ornamental Garden in April
April in Virginia is the party month for gardeners! It’s like putting up the holiday decorations with no thought of putting them away, or getting ready for a party with no thought of washing a mound of dirty dishes at the end. April is FUN! The ground is ready for working, the soil is getting warm enough for seeding, the perennials are showing lots of green, and there is an array of spring-blooming bulbs to enjoy while we’re working in the yard. So, what’s on our list of things to do?
- 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.”
- Transplant on a shady day in late afternoon or in early evening. Water with a half-strength fertilizer solution.
- When transplanting seedlings in peat pots, break away the uppermost rim of the pot before planting and make sure the pot is completely covered with soil. If the rim is above the soil level, it will act as a wick and draw moisture away from the transplant.
- 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.
- As a general rule, divide late-summer or fall–blooming perennials in spring. This includes most ornamental grasses and plants such as asters, chrysanthemums, and canna lilies. Many perennials, however, can be divided in either spring or fall. For a list of perennial division recommendations, see the Virginia Cooperative Extension article, “Dividing Perennials.”
- 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.
- Fertilize spring-flowering bulbs after they finish blooming. An organic fertilizer especially formulated for bulbs is a good choice.
- 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 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.
- Winter mulches should be removed from roses by mid-April. Complete pruning promptly and cultivate lightly with compost. Removed only dead wood from climbers.
- Set out summer-flowering bulbs, such as gladiolus and crocosmia.
- 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.
- Mount a rain gauge on a post or in the ground so that you can track precipitation. Most gardens need about one inch of rain per week between April and September.
April in Virginia offers a beautiful pallet of white, yellow, lilac, and a range of pinks, from ballet pink to magenta. The woods are filled with graceful sprays of dogwoods and redbuds. There are also so many flowering shrubs that shout SPRING!! Look around and see which shrubs you’d like to add to your own landscape. Remember, all of these plants should be pruned and fertilized AFTER blooming, so keep the pruners handy while you’re enjoying the bloom of the ones already growing in your landscape.
Forsythia’s sunny yellow blooms persist for several weeks from March to April and are used by many as a timing device for when to apply spring lawn fertilizers and pre-emergent weed preventers. Forsythia x intermedia is commonly called border forsythia; F. suspensa is known as weeping forsythia. Note: Winter jasmine, Jasminum nudiflorum, is often mistaken for forsythia because of its bright yellow flowers that appear in February.
Both azaleas and rhododendrons belong to the genus Rhododendron, and cover a range of bloom times from early spring to early summer. See the May 2015 Garden Shed article, “What’s So Special About Azaleas and Rhododendrons?”
Camellia japonica and most of its cultivars are considered to be winter hardy to USDA Zones 7-9. In the northern part of its growing range, including Virginia, blooms appear in April. Flower colors are most commonly white, pink, or red with yellow anthers.
Chaenomeles speciosa, commonly called flowering quince, is a dense deciduous shrub with often-tangled, spiny, gray-brown twigs. Scarlet to red (less frequently pink or white) five-petaled flowers bloom before the leaves fully unfold in an often showy early spring bloom (late March-April). Flowers are followed by hard, dot-speckled, edible, yellowish-green fruits (2.5” quinces).
Deutzia gracilis, commonly called slender deutzia, is a dense, rounded, deciduous shrub that produces tiny, fragrant, bell-shaped, flowers. Consider covering the shrub if a hard frost is predicted. ‘Chardonnay Pearls’ is a patented plant best noted for its lemon-lime foliage and profuse bloom of fragrant white flowers in May.
Fothergilla gardenii (dwarf fothergilla) is a slow-growing multi-stemmed shrub that grows 1.5-2’ tall with white, bottlebrush-like flowers in April and very showy fall foliage. F. major, commonly called large fothergilla, tall fothergilla or mountain witch alder, grows 6-10’ tall, and is noted for its aromatic white flowers in April, quality summer foliage, and excellent fall color. See the November 2017 Garden Shed article, “Fothergilla – An Outstanding Choice for Fall Color.”
Spiraea prunifolia, commonly called bridalwreath spirea, is an upright, clumping, deciduous shrub that typically grows 4-8’ tall and is particularly noted for its early spring bloom of double white flowers that appear in April. (Spiraea japonica, commonly called Japanese spirea, blooms in late spring to mid-summer with flat-topped clusters of tiny pink flowers.)
Syringa meyeri, commonly called Meyer lilac or Korean lilac, grows to about 4-5’ tall and has pale lilac to violet-purple fragrant flowers that bloom in small, dense terminal clusters (panicles to 3-4″ long) in late April to early May. Syringa pubescens subsp. patula,’Miss Kim’ is a compact, upright cultivar which grows 4-7′ tall with a similar spread. Lavender to ice blue, sweetly fragrant, single flowers are arranged in dense, terminal clusters (panicles to 3″ long) which cover this shrub in April-May. This is a good selection for southern climates.
Viburnums bloom in the last part of April through early May. Viburnums vary in their height, spread, and style of flower but are similar in preferring sun to part shade and in being disease–and pest–resistant. There are many different species and cultivars, but a very fragrant species often grown in Virginia is Viburnum carlesii, commonly called Koreanspice viburnum. Its red buds open in late March/early April to very fragrant pink-changing-to-white flowers.
- There are excellent lawn care articles from the Virginia Cooperative Extension. The most important recommendation is to 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.”
- Check the fertilizer labels to see the percentages of both WSN (water soluble nitrogen) and WIN (water insoluble N). The higher the WIN percentage the more slowly available the N is to the plant by way of chemical and microbial reactions in the soil. Any source containing 50% or more WIN can be safely applied at higher application rates with minimal concern for nutrient leaching.
- Warm-season grasses don’t initiate much root growth until after shoot greening is complete; therefore, the ideal scenario is to wait at least until 50-75% green-up before applying N. Excessive spring N fertilization promotes a lot of shoot growth and can be disastrous to the turf if there is a late freeze.
- 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.
- Inspect boxwoods (Buxus) for boxwood leafminers (Diptera) as new leaves emerge. Look for blistered, puckered tissue on the underside of boxwood leaves.
- Look for tunneling damage in holly (Ilex) leaf caused by holly leafminer, a fly maggot (Diptera).
- Treat azaleas for lacebugs if they were a problem last year. Look for white flecking on the upper leaf surface.
- Orange, jelly-like galls on cedar trees spread rust diseases to apples, crabapples, and hawthorns. Collect and dispose of cedar-apple galls on junipers and cedar-hawthorn rust on hawthorn leaves and fruit before the orange spore-producing structures emerge from the galls. Immunox is identified as an effective fungicide to protect
against rusts. For a discussion of chemical controls, see section 3-6 on Fungicides in the VCE 2017 Home, Grounds and Animals publication.
- Destroy or prune off webs of eastern tent caterpillars. Manual methods for removal are usually sufficient. Typical natural controls include birds, predaceous and parasitic insects (especially wasps), and disease organisms. Bacillus thuringiensis (Bt, Dipel or Thuricide) is a safe biological spray if an insecticide is needed and should be applied as soon as the tents appear. Most trees, however, will recover from lost foliage.
- Watch for pests, such as slugs and snails, especially after a cool, wet spring.
Alliaria Petiolata, commonly called Garlic Mustard, is a biennial and completes its life cycle in two growing season. First-season plants are ground-hugging rosettes. Second-year plants send up stalks with small white flowers in early spring. As with many invasives, the statistics are discouraging: one plant can produce from 400 to 7,000 seeds. If there is a smaller-sized patch, you can try hand pulling but be aware that there may be other seedlings ready to sprout. Spot-treating with a foliar spray is also an option. See the Factsheet provided by PRISM for more information on identification and treatment recommendations for garlic mustard and other invasives.
Termites are beginning to swarm. Mole young are born in chambers deep underground. If you see a honeybee swarm, notify a local beekeeper to find a new home for these beneficial insects. Hummingbirds return from their winter home in Central America. Wasp and hornet queens begin nesting.