The Ornamental Garden in May

  • By Pat Chadwick
  • /
  • May 2015 - Vol. 1 No. 5

May is the month when nighttime frosts fade into distant memory, the sun feels warm on bare arms, and the ornamental garden bursts into glorious bloom. Peonies rule in mid-May with their gaudy masses of huge white, pink or red blossoms. As if they aren’t eye catching enough, jaunty irises compete with the peonies for attention. Late-blooming tulips carpet the earth in jewel-toned colors. Ornamental Alliums, with their otherworldly globular blooms, rise in salute above their neighbors. Lest you be distracted by this riot of color, there’s much to be done in the ornamental garden. So let’s get started.

Normally, there’s plenty of rain in May. But should there be an absence of precipitation, water your landscape plants deeply and infrequently at a rate of about one inch per week. This is particularly important for new plantings, but it is also essential for maintaining healthy plants throughout the growing season. Even drought-tolerant plants require moisture their first year while they are getting established.

May is a good time to plant a ground cover. If you have a slope, a ground cover will help prevent erosion. If it’s too shady in an area of your lawn for grass to grow, a ground cover may be a good alternative. There are lots of shade-loving options available including Asarum (wild ginger), Galium odoratum (sweet woodruff), Epimedium (barrenwort), and Heuchera (coral bells). Some suggested sun-loving ground covers include creeping thyme, creeping Phlox, creeping oregano, Ceratostigma plumbaginoides (plumbago), Sedum, and Stachys byzantine (lambs ears).

As cool season plants such as violas or pansies begin to wane, replace them with heat-loving plants. Melampodium (butter daisy), Gomphrena (globe amaranth), annual Salvia (sage), Zinnia, Tithonia (Mexican sunflower), Lantana, Tagetes (marigold), Cleome (spider flower), and Verbena are a few “tough-as-nails” annuals that are generally heat and drought tolerant in this area.   Direct sow seeds now or, if you’re transplanting seedlings, make sure they are hardened off before you plant them.

Plant tender bulbs such as Dahlia, Gladiolus, Canna lily, and Alocasia (elephant’s ear) in a sunny spot after the danger of frost has passed. If you don’t have enough sun, then try planting shade-loving Caladium or tuberous Begonia. Or try elephant’s ears in part-shade but make sure you have enough room in your landscape for these behemoths. Depending on the variety, they can grow seriously huge!

Now that the temperatures are consistently warm, the bugs and other creepy crawlies are out in force. Check plants for aphids and treat early before they take over your plants. If lady bugs are present, they may take care of your aphid problem for you. No lady bugs? Then spray the aphids with a stream of water that is strong enough to knock them off the plant but not strong enough to damage the plant.  If that doesn’t reduce the aphid population to a manageable size, spray with a small amount of insecticidal soap.  You can make your own insecticidal soap by mixing one tablespoon of liquid or all-natural soap, such as pure castile soap, with one quart of water in a clean spray bottle. Do not use dishwashing detergents or  liquids that contain additives such as fragrance, degreaser or bleach. Test on a few leaves first to make sure the solution does not harm your plant.

Inspect tender young Hosta foliage for slug damage (holes in foliage). Slugs can do a lot of damage in just one night.  They are normally nocturnal and may not be visible during the day.  Several products are available commercially for controlling slugs, but before using any of them, make sure you read the label and follow the instructions carefully.  Finely crushed eggshells sprinkled around each plant also work well. Slugs don’t like crawling over the sharp edges. Or, place a shallow dish filled with beer at the base of the plant. Slugs will crawl into the dish and drown in the beer. End of problem.

If you see ants crawling on your peonies, don’t worry. Ants are merely attracted to the honeydew on the peony buds and aren’t harming the plant. If you cut a few peony stems for flower arrangements, inspect the blossoms and remove any ants you find before you bring the flowers into your house.

A word of warning: ticks are active now so be alert for them. Check yourself, your children, and your pets after you or they have spent time outdoors. As a preventative measure, wear long pants, closed shoes and socks when working in the garden. Ticks are easier to spot on light color clothing.

Install supports for fast-growing plants that tend to flop. Use stakes and loose ties for delphiniums or foxgloves. Stake dahlias when you plant them. Larger varieties of dahlias tend to fall over, particularly if they are located in a windy spot. Staking them at the time they are planted prevents damage to the tubers. TIP: “Grow-through” ring-style supports work well for peonies and should be installed while the peony foliage is still emerging from the ground.   Otherwise, you’ll find it next to impossible to cage the plant after the foliage matures.

Alas, weeding is an ongoing task but it’s important to keep weeds under control on a continuing basis. Weeds grow fast and they seem to spring up the minute you turn your back on your garden. A few minutes spent weeding every other day or so is time well spent. If you haven’t already applied mulch, spread a layer now to help keep weeds from sprouting. Mulch will also moderate soil temperatures and and retain moisture. Your plants will thank you for your thoughtfulness during the heat of July and August.

Finish acclimating your houseplants to the outdoors but keep a close eye on them so that they don’t become sunburned. Make sure each pot has a drainage hole. If it doesn’t, re-pot the plant into one that does. Lack of drainage is an invitation for root rot.

Pinch out the tops of chrysanthemums when the plants are about four inches high. This will result in a bushier, sturdier, more wind-resistant plant later in the season. Asters also benefit from a pinching now.

Prune spring-flowering shrubs after they finish blooming. Many springflowering shrubs, such as azaleas, set next-year’s flower buds soon after they finish blooming in the current year. If you wait too long to prune, you run the risk of not having any blossoms next year.

If you need a vertical accent in your garden but aren’t ready to commit to a perennial vine, try growing an annual vine such as hyacinth bean, morning glory, or cardinal climber.

The garden centers are filled with lots of interesting container plant choices right now. Take advantage before all the good plants are gone and try planting a container garden. If you’ve never planted one before and are a little nervous about it, relax. Just keep in mind the “thriller, filler, spiller” concept: plant something tall to act 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. Have fun experimenting with color combinations and textures! Just remember to keep container gardens well watered over the growing season.