May in the Ornamental Garden

It’s May and frosty nights are now a distant memory!  The garden centers are abuzz with plenty of exciting new plant choices to try.  Besides planting and transplanting, there’s plenty of weeding, dividing, and general sprucing up to be done in the ornamental garden.

With so many plant choices available to you at this time of year, look for drought-tolerant selections that will require less water once hot, humid mid-summer weather arrives.  Some potential candidates include black-eyed Susan (Rudbeckia), blanket flower (Gaillardia), butterfly weed (Asclepias tuberosa), catmint (Nepeta), goldenrod (Solidago), hyssop (Agastache), mountain mint (Pycnanthemum muticum), purple coneflower (Echinacea purpurea), sneezeweed (Helenium), Stokes’ aster (Stokesia laevis), and yarrow (Achillea millefolium).   Important:  Although these plants are drought tolerant, they require ample moisture their first year while they are getting established.

With our last average frost date behind us, it’s now time to direct sow seeds of heat-loving annuals such as cosmos, marigolds, cleome, gomphrena, or zinnias.  After the plants reach 4 to 6 inches in height, pinch them back to promote bushier growth.  This will ultimately produce more flowers.

Transplant bedding plants on a cool, calm, cloudy day.  The cooler temperatures and cloud cover will cause less stress to the plants and will help them settle in sooner.  Some common fast-growing annuals that are sold as bedding plants include celosia, dusty miller, geraniums, lantana, lobelia, petunias, portulaca, salvia, and begonias.

Plant tender bulbs such as dahlias, gladioli, or cannas in full sun. If you don’t have full sun (at least 6 hours per day), try planting shade-loving caladiums and tuberous begonias.  For a touch of drama, try growing elephant ears in part-shade but give them plenty of room.  Depending on the variety, they can grow seriously huge!

Install supports for fast-growing plants that tend to flop.  Secure tall plants such as delphiniums or foxgloves to a single stake using jute or other soft twine.  For mounding plants such as peonies, use “grow-through” ring or grid-style supports.

Protect newly planted seedlings and transplants from drying wind and hot sun for the first few weeks while they establish strong root structures.  Keep the soil around the fragile roots moist but not soggy. If the root ball dries out, the plant may not recover from the stress.  Too much water is just as bad for seedlings and transplants because soggy soil may cause their roots to rot.

Monitor moisture requirements of newly planted trees.  In general, it takes 2 to 3 years or more for a tree to become established in the landscape.  Adequate moisture is particularly critical during this period to encourage healthy root development beyond the original root ball.  In the absence of good soaking rains, provide supplemental water, particularly as daytime temperatures grow hotter.   Cover the entire area under the tree canopy to keep the soil evenly moist but not soggy around the root ball and surrounding soil.

Prune spring-flowering shrubs after they finish blooming.   If you put off doing this until later, you run the risk of cutting off the buds for next year’s blooms.  Virginia Cooperative Extension (Va. Coop. Ext) Publication 430-462, Shrub Pruning Calendar, provides guidance on the best time of year to prune a variety of shrubs.

Lightly fertilize azaleas and rhododendrons after they finish blooming if a soil test indicates that nutrients in the soil are low.  Use a fertilizer that is specially formulated for acid-loving plants and follow the directions carefully.  Lightly scatter the fertilizer at the edge of the root zone.  Azaleas have delicate roots that are close to the soil surface and can be easily burned by excess fertilizer.  Too much fertilizer may also cause scorched leaf margins.

Finish acclimating your houseplants to the outdoors by gradually increasing their exposure to sunlight.  Monitor them carefully so that they don’t become sunburned.  Make sure each pot has a drainage hole.  Lack of good drainage is an invitation for root rot.

Experiment with container gardening if you’ve never tried it before. For best results, keep in mind the “thriller, filler, spiller” concept: plant something tall as a focal point, something mid-size to fill in around the “thriller,” and something low that cascades over the rim of the pot and softens the overall effect.  Just remember to keep container gardens well watered over the growing season.

Incorporate pollinator-friendly plant species that attract bees, flies, butterflies and other pollinating insects to your ornamental garden.  Flowers with single petals rather than double petals are generally a better choice. Echinacea (cone flower) and zinnias are examples of plants that have undergone significant breeding for fuller, showier flowers. While they offer more variety and pizzazz for the garden, the downside is that such breeding efforts affect the flower’s ability to produce pollen.  In order to produce double flowers, the stamens (male portion of the flower) are bred to transform into extra petals. Because of this alteration to the basic anatomy of the flower, the blossom may not produce as much pollen as a flower having single petals.

Replace mulch with ground covers in your landscape.  Mulch is useful in holding moisture in the soil, moderating soil temperatures, preventing erosion, and controlling weeds.  However, in certain situations, such as under trees where grass struggles to grow in the shade, a living ground cover instead of mulch may be a more practical solution.  Like mulch, ground covers 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. Consider planting native ground covers such as:  wild ginger (Asarum canadense), green and gold (Chrysogonum virginianum), Allegheny spurge (Pachysandra recumbens), foamflower (Tiarella cordifolia), blue-eyed grass (Sisyrinchium angustifolium), and creeping phlox (Phlox stolonifera).

Monitor your prized plantings for pests of all kinds – creeping, crawling, flying, etc.  Here are a few to be on the alert for in May:

• Aphids – These voracious insects have mouth parts that are designed to pierce and suck the sap from a plant. They damage plants by causing yellowing, stunted growth, mottled leaves, browning, and even plant death. Ladybugs and lacewing larvae are the natural predators of aphids and may control them for you.  If not, then a sharp spray of water is usually sufficient to dislodge aphids from plants. See the University of Maryland extension website for additional information and photos of aphids on a variety of plants.
• Slugs – These nocturnal members of the mollusk family can do a lot of damage in just one night – especially to hostas. To eliminate these slimy creatures, take a flashlight outside after dark, hand pick any slugs you find (wearing gardening gloves, of course), and drop them into a container of soapy water.  If that approach doesn’t appeal to you, sprinkle finely crushed eggshells around vulnerable plants.  Slugs don’t like crawling over the sharp edges.  Another approach is to use a shallow dish filled with beer to entice slugs.  Any brand of beer will do.  Just nestle the dish into the soil leaving about half an inch of the rim exposed above ground. The slugs crawl into the dish and drown in the beer.  End of problem.  The University of Vermont extension’s website offers good advice on controlling slugs.
• Ticks – Ticks are arachnids rather than insects and are at their most active between May and July. During this time, wear light colors, closed-toe shoes, socks, long pants and long sleeves when working outdoors. Don’t forget to tuck pant legs into socks. Check yourself, your children, and your pets after you or they have spent time outdoors.  For a description of the primary types of ticks found in Virginia, see VCE publication 2906-1396 “Common Ticks of Virginia.”
• Eastern Tent Caterpillars are the larval form of an ordinary looking yellowish-tan to brown moth (Malacosoma americanum). The hairy larvae hatch out in spring at which time they spin unsightly “tents” of silk webbing where they spend their nights.  They emerge from the tents in the daytime to feed on the host plant, stripping it of its foliage.  Insecticides are generally not effective when tent caterpillars are inside their tents.  VCE publication 444-274, Eastern Tent Caterpillar offers more information on this insect.  While tent caterpillars can be destructive to trees and shrubs, they are also an important food source for some bird species.  Before deciding to kill the larvae, check out Entomologist Michael J. Raupp’s  Bug of the Week website which provides useful information on tent caterpillars.  While not many bird species will eat hairy caterpillars, the yellow-billed cuckoo is one bird species that will, according to Cornell University’s All About Birds.

Bad bugs get all the press but there are far more good bugs than bad, including:

• Praying Mantis — If you spot a praying mantis in your landscape, leave it alone.  These large, green or brown, stick-like beneficial insects blend in well with their surroundings and are sometimes hard to spot. Mantid eggs overwinter in a small tan, frothy-looking, hardened case (ootheca) 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, mantids 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.

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  Syrphid Fly (Sphaerophoria philanthus) – Syrphid flies (also called hover flies or flower flies) serve double duty as both pollinators of a wide variety of plants and predators of other insects. These small black and yellow-striped insects measure less than ½ inch long and are often mistaken for bees or wasps.  However, Syrphid flies don’t have stingers and, like all fly species, they have only one pair of wings, whereas bees and wasps have two pair.  In their adult form, syrphid flies feed only on pollen, nectar and aphid honeydew and do not prey on other insects.  As larvae, they are highly effective natural enemies of aphids, scales, thrips, and other soft-bodied, slow-moving insect species.  Just one larva can consume hundreds of aphids.  For photos of both the adult and larval forms of this beneficial insect, see North Carolina State University Extension’s publication on Syrphid Flies.

Take preemptive steps to keep deer out of the garden.  As beautiful as deer are, they can do a devastating amount of damage to plants that are just emerging or leafing out.  A tall fence or other physical barrier is the most effective way to keep deer out of your garden.  If a fence is out of the question, then try growing plants with strong scents (such as herbs), tough or leathery foliage, and spiky or spiny foliage.  Confuse deer by tucking vulnerable plants in among plants they normally shun.  Use repellents that either smell or taste bad to deer.  Repellents that have a sulphur-based odor of rotten eggs appear to be more effective than taste-based ones but alternate their use so that the deer don’t become accustomed to them.  To learn more about deer and strategies for living with them, see Garden Shed article Deer, Deer, Deer!, which provides lots of great information on the subject.

Invasive Alert:  Spring rains make the soil moist and easy to work in, which makes conditions ideal for homeowners to hand pull small, young sprouts of invasive plants.  To control these species, it’s important to remove all parts of the root so that the plant cannot regrow.  Look for the following species:  English ivy (Hedera helix), climbing euonymous (Euonymous fortunei), Japanese honeysuckle (Lonicera japonica), Oriental bittersweet (Celastrus orbiculatus), Japanese barberry (Berberis thunbergia), autumn olive (Eleagnus umbellata), wineberry (Rubus phoenicolasius), and garlic mustard (Alliaria petiolata).  Visit the Blue Ridge PRISM (Partnership for Regional Invasive Species Management) website for factsheets on each of these species, including photos and control options.