The Ornamental Garden in May
With warm weather comes the inevitable spring gardening chores – loosening and amending the soil for planting, pulling weeds, redefining the edges of flower beds, pruning, mulching, dividing plants, etc. While that sounds like a lot of work, it’s all in preparation for the main event: planting the spring garden. This is what every gardener dreams of – that time of year when we can dig in the dirt, forget all the stresses of modern society, and focus on making something good and beautiful grow from the soil. So let’s get the chores out of the way and have some fun, shall we?
Irises are at their peak this month, but the spent blossoms can turn to a gooey mess, especially after a rainstorm. As you snap off each spent iris blossom, be careful not to break off any unopened buds. Removing the spent blossoms not only tidies up the plant but also prevents it from setting seed. After the last flower starts to fade, cut off the flower stalk at the base with a sharp knife. Sterilize the knife between cuts to prevent spreading disease among the plants.
Peonies are also at their glorious best in May. After they finish blooming, the foliage can continue to look attractive in the summer border provided you do a little maintenance. In late May or early June, cut back the spent flower stalks to improve the shape and appearance of the plant. Simply reach down inside the plant and snip off the stalk just above a set of leaves so that the cut end isn’t visible. That keeps the plant looking tidy and diverts the energy from seed-making to growing a more vigorous plant.
Prune lilacs (Syringa vulgaris) after they finish blooming. Lilacs that have not been well maintained, particularly the common old-fashioned upright varieties, can become overgrown and awkward looking with age. In addition, older lilac stems produce fewer and smaller clusters of flowers. Because lilacs bloom on the previous year’s growth, timing is important when it comes to pruning. Here are some tips on how and when to prune:
- Rejuvenation pruning – If the shrub is seriously overgrown, it may be best to cut the entire plant back to about a foot from the ground. The best time to do this is late winter or early spring when the shrub is dormant. The plant will recover within two or three years but the downside is that the plant may not flower in the meantime.
- Selective rejuvenation pruning – If you are loathe to sacrifice all of next year’s floral display, then cut the shrub back in stages. Selectively cut back a third of the oldest stems all the way to the ground each year in late winter or early spring. While you are at it, remove all dead, damaged or diseased branches, as well as any crossing branches or small branches that are the diameter of a pencil or less. This will help open up the shrub, thus increasing air circulation.
- Size maintenance or reduction – To maintain or slightly reduce the shrub’s size, prune the tips of stems back yearly to a pair of side shoots immediately after the shrub finishes blooming. This promotes new growth and allows the new shoots adequate time to set buds for next year’s flowers.
- Deadheading — Cut off each spent flower cluster at its base immediately after the shrub finishes blooming. This diverts the plant’s energy into growing new shoots and flower buds.
If pruning doesn’t appeal to you, try one of the newer dwarf lilac varieties. They are much easier to maintain, requiring little, if any, pruning. As a bonus, some of them even rebloom during the growing season. For basic information on lilac species, see Virginia Cooperative Extension (VCE) publication 3010-1493, Lilacs, Syringa spp.
If you have flower seedlings to transplant, harden them off first before you plant them outdoors. Move them to a shaded spot, preferably on an overcast day, and then gradually introduce them to sunlight over a week or two. Once they are hardened off, plant them at the same depth as they were in the container and keep them well watered until they become established. Watch night-time temperatures and be prepared to protect the seedlings should the unthinkable happen and we have a late frost.
In you’re tired of spreading mulch every year, try a more permanent – and prettier – solution. Incorporate more ground covers into your landscape. Like mulch, ground covers can shade the soil, hold it in place, and smother weeds. On top of the practical aspects of ground covers, they add an attractive layer of color and texture in the landscape. If you’re interested in native ground covers, consider planting: wild ginger (Asarum canadense), green and gold (Chrysogonum virginianum), Allegheny spurge (Pachysandra recumbens), Sedum ternatum, foamflower (Tiarella cordifolia), and blue-eyed grass (Sisyrinchium angustifolium). Most of these prefer shade to part sun.
Moss phlox (Phlox subulata) is a native ground cover that grows in full sun but will tolerate part shade. It’s also deer resistant but rabbits may nibble it. Creeping phlox (Phlox stolonifera) is another phlox species suitable for full sun or part shade. Neither deer nor rabbits bother this species normally. Another interesting ground cover for full sun is lamb’s ear (Stachys byzantina), a non-native but well-behaved plant. The low-growing, non-blooming ‘Silver Carpet’ cultivar spreads about a foot or so wide, adds a silvery element to the garden, and provides a pleasant, fuzzy texture. It’s drought tolerant, deer resistant and looks good as an edging to a defined flower bed. Just give it full sun and very well-drained soil.
ANNUAL, BIENNIAL, PERENNIAL – WHAT’S THE DIFFERENCE?
Confusion often arises about the differences between annuals, biennials, and perennials. Even seasoned gardeners sometimes get confused. Global warming notwithstanding, part of the problem is that some plants are technically perennial in one gardening zone but must be treated as annuals in less hardy gardening zones. Variances within species don’t help any. For example, most foxglove species (Digitalis purpurea) are biennial whereas Digitalis grandiflora is perennial. Scabiosa is another confusing species with an annual form (Scabiosa atropurpurea) and several perennial forms, including Scabiosa caucasica and Scabiosa columbaria. To add to the confusion, some annuals readily re-seed before they die and those seeds then germinate the following spring. If they germinated in the same spot as the original plant, the gardener may be tricked into thinking the original plant re-sprouted.
The following may help explain the differences among the three categories.
- Annuals complete their life cycle in one growing season. They germinate from seed in the spring, bloom and set seeds during the summer. The entire plant then dies with the onset of winter. In other words, annuals are not hardy. They cannot survive winter weather. Examples of annuals include bachelor’s buttons, balsam, marigolds, petunias, statice, sweet peas, and zinnias.
- Biennials complete their life cycle in two growing seasons. In year one, they germinate from seed in the spring. In summer they form leafy plants, often in the form of a rosette, but they do not bloom the first year. The rosette goes dormant in cold weather but does not die with the onset of winter. In year two, the plant blooms, sets seeds, and then dies. Biennials include alyssum, rose campion, stock, sweet William, some hollyhocks, and most foxgloves.
- Perennials are hardy enough to survive winter weather and live more than two years. While the top part of the plant dies back in autumn, the plant’s crown or roots go dormant in winter. In the next growing season, the plant sends up new foliage and flowers from the crown. The life cycle of perennials varies widely among plants. Peonies, ferns, and Baptisia are examples of perennials that can live for decades. In fact, peonies may live 50 to 100 years or more. Columbine, Shasta daisies, and Delphinium are examples of perennials that may live only a few years.
WHAT TO PLANT UNDER A BLACK WALNUT TREE
Although black walnut trees (Juglans nigra) are prized for their fine-grained wood and edible nuts, they pose a real dilemma in the urban landscape. Very few plants can tolerate the soil beneath a black walnut tree. All parts of the tree contain juglone, a toxic substance that inhibits the growth of anything planted either under or near it. If you have such a tree in your landscape, don’t despair.
To reduce the effects of juglone:
- Rake up all fallen leaves and nuts as they fall. Don’t procrastinate. It’s important to remove all debris before it has a chance to break down and be absorbed into the soil.
- Incorporate lots of organic matter into the soil beneath the tree. This supports a healthy microbial population, which can metabolize the juglone toxins.
- Install juglone-tolerant ornamental plants beneath black walnut trees. Luckily, some suitable plants include asters, monarda, day lilies, hardy geraniums, and hostas. For more information on plants that can tolerate juglone, see VCE publication 430-021, “The Walnut Tree: Allelopathic Effects and Tolerant Plants.” Another good source of information is the Morton Arboretum’s publication on Plants Tolerant of Black Walnut Toxicity.
INSECTS IN THE MAY LANDSCAPE – THE GOOD, THE BAD, AND THE UGLY
Along with the emergence of spring growth comes the inevitable hordes of insects – both good and bad. Several to watch for in May include:
If you spot a praying mantis in your landscape, leave it alone. Whether you think of it as friend or foe, it is one of the more interesting insects in the garden. Either green or brown, they are large, stick-like creatures that blend in well with their surroundings and are sometimes hard to spot. A member of the mantid genus, this fascinating predator gets its common name from the way it holds its prominent front legs at an angle, suggesting it is praying. In the fall, the female lays her eggs in a small tan, frothy-looking, hardened case (called an ootheca). The eggs overwinter in the case and then hatch out around early May. Young praying mantids eat small insects whereas the mature versions tackle big insects, such as crickets, grasshoppers, cabbage moths, and stink bugs. Unfortunately, they make no distinction between bad bugs and beneficial ones and eagerly gobble up both. However, in general, they appear to do more good than harm in the environment.
May to July is prime tick season. For a description of the four primary types of ticks found in Virginia, see VCE publication 426-066, “Gardening and Your Health: Ticks.” In the meantime, you can take a number of steps to keep the tick population at bay:
- Avoid letting your lawn get out of control. Ticks like the high humidity that tall grass provides.
- Install plants that are deer-resistant. Deer are major carriers of ticks.
- Eliminate brush piles, leaf litter, downed branches, and other debris that might appeal to ticks and their hosts (such as white-footed mice).
- Move picnic tables, swing sets, and other recreational equipment away from shrubs or wooded areas. Place children’s play equipment on a bed of wood chips.
- When working outdoors during tick season, wear light colors, closed-toe shoes, socks, long pants and long sleeves. Tuck pant legs into socks.
- Install gravel or wood chip pathways between the house and any frequently used outside areas.
- Install a 3-foot wide wood-chip barrier along the perimeter of a wooded area.
THE UGLY: Eastern Tent Caterpillars are the larval form of an ordinary looking yellowish-tan to brown moth (Malacosoma americanum). In mid-summer, the adult moths lay their egg masses on twigs. The masses contain 150 to 400 eggs, which overwinter and then hatch out in spring. That’s when things get ugly.
The larvae are 2- to 2-1/2” long, hairy caterpillars with a white stripe bordered by yellow-brown and a row of blue spots along their sides. After hatching out, the writhing masses of larvae move to the nearest branch crotch where they spin unsightly “tents” of silk webbing. The larvae spent their nights inside the tents. In the daytime, they emerge to feed on the host plant, stripping it of its foliage. This goes on for about 4 to 6 weeks, at which time, the individual caterpillars wander off to protected areas where they spin little cocoons. Three weeks later, they emerge as adult moths and the cycle begins all over again.
Insecticides are generally not effective when tent caterpillars are inside their tents. The best way to control them is to snip off the twig (if it is small) containing the larvae inside the tent and burn or crush it, killing all the larvae inside. If the branch containing the tent is larger, insert a long stick into the tent. Twist the stick around so that the silken tent adheres to it. Pull the entire mass away from the branch and then burn or crush all the larvae. VCE publication 444-274, Eastern Tent Caterpillar offers more information on this destructive pest.
STRATEGIES FOR KEEPING THE DEER AT BAY
For those of us who must contend with deer in the garden, spring can be a particularly aggravating time. As beautiful as these creatures are, they can do a devastating amount of damage to plants just as they are emerging or leafing out. This is when you need to figure out ways to control deer damage. Unfortunately, there’s no one-size-fits-all solution. A deer’s food preferences vary by season, the particular plant, the availability of other food, the weather, and the locality. Bottom line, the hungrier the deer, the less selective they are when grazing in your ornamental garden. A tall fence or other physical barrier is usually the most effective way to keep deer out of your garden. A dog that can roam freely on your property is also a good deterrent. However, if you don’t have a fence or a dog, don’t despair. Several other strategies, listed below, may help. Whatever measures you take will work best if exercised at the first indication of deer browsing. The idea is to prevent them from becoming accustomed to visiting your property.
- Grow plants with strong scents, tough or leathery foliage, and spiky or spiny foliage. Deer generally avoid such plants unless they are really hungry.
- Confuse deer by tucking vulnerable plants in among plants they normally shun.
- Install nylon or wire mesh fencing around vulnerable young trees and shrubs. Don’t use flimsy bird netting. A deer can become entangled in it, which is neither good for the deer nor for you.
- Use repellents that either smell or taste bad to deer. Alternate their use so that the deer don’t become accustomed to them. Repellents that have a sulphur-based odor of rotten eggs appear to be more effective than taste-based ones.
- Get creative. For example, I discovered that deer avoided my tall sedum if I left the dried flower heads in place all winter. Rather than cut the stalks down to the crown in spring, I merely snipped off the flower heads but left the stalks in place. The spiky flower stalks towering over the sedum crowns looked vaguely like something Salvador Dali might have painted. However, they protected the new spring growth from deer browse. Eventually, the new growth covered up the old stalks. By then, the deer, thankfully, had moved on to greener pastures.
If all else fails, adjust your thinking. Let’s say, for example, that the deer nibbled your azaleas. That’s the bad news. But if the shrubs needed to be pruned back anyway, then the deer merely helped. That’s good news. So think of it as a win-win situation.
HOW TO ENTICE BLUEBIRDS TO YOUR YARD
Lucky is the homeowner who has bluebirds nesting nearby. There’s no mistaking the identity of this bird with its exquisite, vivid blue foliage. It is not only beautiful but also useful because it helps keep insects under control in both the ornamental and the vegetable garden. Enticing bluebirds to your yard can be a bit of a challenge, however. They prefer open areas with a wide expanse of low grass as well as shrubs or small trees that offer them a place to perch as they scan the area for insects. To entice them to your property:
- Provide nesting boxes. Bluebirds generally produce two clutches of eggs per season, one in spring and one in summer. They are cavity nesters and, in the wild, must compete with house sparrows and other cavity nesters for naturally occurring cavities in dead trees. So, offer them a nesting box built to their specific needs. Install it in an open area about 100 to 150 feet away from any wooded areas. Bluebirds are territorial, so if you build more than one nesting box, space them 300 feet apart. Position the box 4 to 6 feet off the ground with the opening at 5 feet (eye level) and facing east (toward open habitat and away from the prevailing winds). Download bluebird house directions from the Cornell Lab of Ornithology website Bluebird House.
- Supplement their diet. Between spring and fall, bluebirds eat mainly insects. For that reason, avoid using pesticides or other chemicals. Supplement their diet with mealworms, particularly in winter when insects are not available. Also, they like to round out their diet with berries from trees and shrubs, such as Eastern red cedar, flowering dogwood, holly, hackberry, elderberry, beautyberry, serviceberry, and blackhaw.
- Provide a source of water. Bluebirds appreciate a birdbath, but, if possible, provide them with moving water, which they prefer. A small fountain or even a dripper will appeal to them.
TIME TO GIVE YOUR HOUSEPLANTS A SUMMER VACATION
After the last frost date, move your houseplants to a shaded area outdoors. After being cooped up all winter indoors, they will be sensitive to both light and temperatures. So, gradually condition them to the higher light levels and warmer temperatures. This may take a week or two, depending on the weather. If the overnight temperatures drop below 50°F, either cover your plants to keep them from going into shock or return them to the indoors for the night.
With fresh air and brighter light outdoors, your houseplants will enjoy a rapid growth spurt. Before that happens, check to see if the plants need to be repotted. If so, pot them in a slightly larger pot with fresh potting soil and give them some plant food to support their growth.
As your houseplants become acclimated to the outdoors, check moisture levels daily. Potted plants tend to dry out quickly, particularly once the weather turns consistently hot.