In the Ornamental Garden — Tasks & Tips for May

In the Ornamental Garden — Tasks & Tips for May

  • By Pat Chadwick and Cathy Caldwell
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  • May 2020-Vol 6 No. 5
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The Piedmont Master Gardeners website has a new feature:  monthly gardening tasks and tips are now appearing under Gardening Resources on the main page of the PMG website.  For more May tips, take a look at Gardening Resources/Monthly Gardening Tips/Piedmont Master Gardeners

Here’s our To-Do List for May:

  • To encourage fuller, sturdier asters and chrysanthemums, pinch them back by about a third this month and again in June or early July.  Pinch back chrysanthemums as soon as the new shoots are 4 to 6 inches long.  Just grasp the growing tip and pinch about ½ to 1 inch of the stem back to a leaf node.  The plant will push out new branches from these nodes.  Those branches in turn will need to be pinched back by the early part of July.
  • 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.
  • 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.
  • Stake tall-growing plants that are susceptible to wind damage. Loosely tie the plant to the stake in a figure-eight configuration with the knot against the stake (not the stem of the plant).
  • If mosquitoes are a problem, incorporate plants that naturally repel them such as scented geranium, lemon balm, southernwood, catnip, nicotiana, marigold, lemon thyme, peppermint, and lavender.
  • Zinnias are easy to grow from seed and make a great cut flower.
    Photo: Cathy Caldwell

    Direct sow seeds of annuals such as cosmos, marigolds, cleome, gomphrena, or zinnias in the early part of May. Later, when 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. Also, pinch off any buds or open blooms so that the plant will concentrate its energy into root development. A little delayed gratification now will mean a healthier, more floriferous plant later.
  • Provide adequate water to newly-planted seedlings and transplants and protect them from drying wind and hot sun until they establish good root structures. This is particularly important during the first few weeks for healthy root development. Lack of moisture is one of the key reasons young plants die before they become established.  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 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.  Don’t take it for granted that light spring rains will provide enough moisture at the root level.  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.  Too much water can be as detrimental to the health of a tree as too little.
  • Snip off the seed heads of daffodils and other spring-flowering bulbs after the flowers are finished but leave the foliage alone so that it continues to photosynthesize. Just let it die back naturally.  TIP:  Plant some fast-growing annuals nearby so that they can camouflage the dying bulb foliage.   Petunias, lantana or verbena are good choices for this purpose.
  • Prune spring-flowering shrubs after they finish blooming.   If you put off doing this until later, you run the risk of cutting off 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.  And for expert guidance on pruning, be sure to review a recent Garden Shed article on that topic:  A Pruning Primer, The Garden Shed, Feb. 2020.
  • It’s time for your houseplants to move outside for their summer vacation.  You can safely move them once night-time temperatures are stabilizing above 50° F.  To get the plants ready for their summer home, water each one thoroughly.   Rinse off the foliage with room-temperature water to remove dust and dirt that may have accumulated over winter. Groom each plant by removing any dead or dying leaves.  Re-pot any plants that have outgrown their pots.   For plants that don’t need to be re-potted, top off the soil with an inch or two of fresh potting soil.  Gradually acclimate the plants by placing them in a shady location initially while they adjust to brighter light.
  • Start inspecting plants for signs of disease or pest damage. Address any little problems before they become big ones.  Lots of April showers can lead to spots on leaves, fungal rots, and the like.  One common fungal disease among rhododendrons and a number of other shrubs is Botryosphaeria dieback.  To see what it looks like and to learn more about it, watch this video from Va. Cooperative Extension:  Video: Botryosphaeria Dieback – Common Plant Diseases in the Landscape and Garden
  • KEEP ON WEEDING!  You’re lightening your weed load for next year.

For more May tips, take a look at Gardening Resources/Monthly Gardening Tips/Piedmont Master Gardeners


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