May

Plant
  • Set out annuals after danger of frost is past. Transplants become less stressed when set out on a cloudy, calm day. Set out in late afternoon and protect from strong light and wind.​
  • Plant annual flower seeds.
  • Plant dahlias and cannas after last frost date.
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Prune
  • Continue pruning spring flowering trees and shrubs after they bloom. Van Houten spirea, lilac, forsythia, and mock orange should be pruned by removing the oldest and largest canes at the base of the plant.
  • Dead head peonies.
  • Pinch mums and asters until July 4.
  • To keep pine trees small, remove 1/2 of the candle of new growth. Removing all new growth will result in base branches as pines drop their oldest needles each fall.
  • Cut back and layer perennials such as phlox, Joe Pye (when 3' tall), NE asters (when 24" tall) and monarda to control height.
  • Shear candytuft back after blooming to promote bushiness.

Chores
  • Take or provide support for tall growing perennials or ones that tend to flop.
  • Continue weeding and mulching.
  • For powdery mildew on phlox, lilac, and monarda, spray with dormant oil.

Tips
  • To increase the number of foxglove in your garden, gently bend the finished flowering stalk down to the ground. When the seed pods are brown and totally dry, rub them onto the ground. When the new seedlings are big enough, transplant them to where you would like to have them in your garden. They will flower in 2 years (foxglove are biennials). Do this each year and you will have a garden full of foxglove.
     
Phenological Plant and Plant Pests
A useful tool for successful gardening is an insect calendar. This will tell you what bugs are typically active in each month. We all know that with changing weather patterns, plants are sometimes blooming either earlier or later. So, an even better way to monitor insects is with phenological plants. These are indicator plants: their bloom time coincides with certain insects in the environment. 
Horsechestnut/Fringetree Blooming
  • Lesser peach tree borer. Clearwing moths lay their eggs in the limb crotches of cherry trees (especially young ones).
  • Euonymous scale: white (male) and brown (female) specks (scales) encrust stems and leaves. They are sapsuckers. Adult scales are protected from insecticides by waxy coverings. Control measure, therefore must be aimed at the unprotected immature stage. There are 2 generations per year. Rx: Spray with dormant oil in early spring.
  • Holly leafminer. Light infestations require no attention other than to pick off and destroy infected leaves.
  • Pine needle scale. Rx: spray with dormant oil.