The Ornamental Garden in April
April teaches us lessons in both vigilance and patience. Bright sunny days and warm spring breezes lull us into thinking cold weather is behind us. But we need to stay vigilant for sudden dips in nighttime temperatures that can result in deadly overnight frosts. If spring rains make the soil too wet to work, we must be patient and wait for drier gardening conditions.
If a frost is forecast, protect tender new growth with row covers, old sheets, cardboard, or even layers of newspaper. Just remember to remove the coverings the next morning. Otherwise, you may accidentally “cook” your plants as day-time temperatures rise.
Note the location of emerging spring bulb clumps. If you haven’t drawn a plot of your garden, now is a good time to sketch one before bulb foliage dies back. This map will come in handy later to help you avoid digging into and damaging the bulbs. Another good habit is to use a garden journal to record the location, cultural requirements, and other useful information about each of your plants.
Fertilize spring-flowering bulbs after they finish blooming. An organic fertilizer especially formulated for bulbs is a good choice. Avoid using a high-nitrogen fertilizer which may promote lots of lush-looking foliage at the expense of flower production next spring.
Cut daffodil and hyacinth flower stalks to the ground after they finish blooming. Why? Because you want the bulbs to focus on storing energy for next year’s blossoms and not on developing seed heads. Do not cut the foliage. Also, don’t braid it or tie it because this interferes with photosynthesis. Just let the foliage die back naturally. The leaves are needed to produce strong bulbs for next season’s blossoms.
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 so that you can find it later in the summer after the foliage has died back. A golf tee, plastic knife, or wooden stick is useful for this purpose. Make a note to dig up and separate the bulbs in July.
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 (http://www.pubs.ext.vt.edu/450/450-600/450-600.html). Iris borers are another common problem. Borer larvae 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 in the edges of center foliage and slimy frass. If you detect the presence of a borer caterpillar in the leaf, crush it with your fingers. If the borer gets to the rhizome, this pest will hollow it out and then proceed to other rhizomes. Bacterial soft rot often follows borer damage. Removal of all dead or damaged leaves in the fall is the best way to control this pest. Either burn the foliage or dispose of it in the trash. Do not compost diseased irises. See the American Iris Society website for additional information on iris pests and diseases (www.irises.org).
As you select new plantings, avoid plant species that are potentially invasive in this area of Virginia. Instead, consider using native plants that minimize maintenance, require less water, and increase habitat, particularly for beneficial insects. If you’re interested in learning more about native plants, a number of excellent resources are available on the subject. For example, see the Virginia Native Plant Society’s website at http://vnps.org/ or check out the Albemarle County Recommended Native Plants website at http://www.albemarle.org/nativeplants/. The Virginia Department of Conservation and Recreation’s Natural Heritage Program at www.dcr.virginia.gov/natural_heritage/nativeplants.shtml is yet another excellent resource. Also, see Cathy Caldwell’s article on invasive plants in the February 2015 issue of The Garden Shed.
Before digging holes for new plantings, keep in mind the ultimate size of each plant. Allow ample space for growth and good air circulation. Also, group new plantings according to similar needs for water, fertilizer and sun. Don’t forget to update your garden plot or garden journal showing the location of your new plantings.
Spring is the time to divide perennials that bloom later in the growing season. Most perennials benefit from being divided every three to five years. Once the soil is dry enough to work in safely, divide perennials such as fall asters, chrysanthemums, shasta daisies, baby’s breath, coneflowers, Rudbeckia, ornamental grasses, sneezeweed, Boltonia, false chamomile, coral bells, leopard plant, and bee balm. Alternatively, most spring-blooming perennials should be divided in the fall.
Pinch back chrysanthemum foliage this month when the plants are about four inches high. This will make a bushier, sturdier, more wind-resistant plant later in the season. False sunflower (Heliopsis helianthoides) is another plant that benefits from being pinched back in spring to shorten the plant. This late summer-blooming native perennial may be divided in either fall or spring.
Deadhead the spent blooms of Lenten rose (Helleborus orientalis) to tidy it up while the foliage is filling in. Be careful not to snip emerging new foliage by accident.
When shopping for bedding annuals from nurseries, choose healthy plants with well-developed root systems that are not too large for their pots. As you plant them, pinch off any blooms so that the plant diverts its energy into developing a healthy root system. Yes, you may be reluctant to do this, but sacrificing a few blossoms initially will reward you with healthier, more floriferous plants later. If you’re new to gardening and would like more information on growing annuals, see VCE Publication 426-200, Annuals: Culture and Maintenance (http://www.pubs.ext.vt.edu/426/426-200/426-200.html).
Keep new bedding plants evenly moist while they are developing sturdy root systems but don’t drown them. Too much water may cause the roots to rot.
If you start your own annuals indoors from seed, gradually introduce the seedlings to the outdoors. Place them in a shady location initially and bring them indoors at night if temperatures are predicted to drop below 50°F. Gradually leave the plants outside for longer periods of time until they are fully acclimated and can be safely planted outside. Remember – a frost can occur up to about mid-May in the Albemarle County area, so be careful not to plant seedlings outside too soon. Tip: Your bedding plants will acclimate better if you plant them on a cloudy day. If that’s not possible, then plant them late in the day when temperatures are cooler.
Move your houseplants outside, once night-time temperatures consistently stay at 50° F. or higher. But before you do, repot any root-bound plants in slightly larger pots. Fertilize with a slow-release fertilize or with fish emulsion. Place your plants in a shady area initially so that they can gradually acclimate to being outside.