University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article

Charlie Nardozzi, Horticulturist and
Leonard Perry, UVM Extension Horticulturist
Pruning lilacs, controlling iris borers, and proper weed whacking are some of the gardening activities for this month.

After lilacs finish flowering, you can “deadhead” or prune off the old blossoms. To reduce the height of the shrub, prune the old stems to the ground and allow new suckers to grow and flower.   If plants are large, taking one-third of the old stems out over a three-year period doesn’t create the dramatic butchered effect of pruning all at once.  Some prefer to prune in late winter when it is easier to see the branch structure.  Pruning early, though, will remove this year’s flower buds which begin forming right after bloom of the previous year.

Check bearded iris leaves for yellow streaks and mushy spots in the plump surface roots called “rhizomes”. These are sure signs of iris borer activity. Check the rhizomes for borer holes and remove infested parts.  In the future, avoid covering rhizomes with mulch or soil (this favors borer activity),  or grow resistant Siberian iris instead.

If you're using a string trimmer to trim around trees, be careful not to damage the tree bark.  Repeatedly striking tree bark with weed whacker strings opens the tree to infection, and may over time kill the tree by cutting through the tender bark.  Technically, this is known as “girdling”.  Mulch around trees so you don't have to trim close to the trunk, or place tree guards on the trunks.  Just make sure you don’t pile mulch up around the trunks.

Young cucumber, melon, and squash plants are easy prey for cucumber beetles. As the seedlings grow, these yellow-striped or yellow-spotted beetles emerge to feed on the foliage. The beetles also spread bacterial wilt disease. To control them in a small planting, cover plants with a lightweight white fabric referred to as a “floating row cover”, spray pyrethrum botanical spray, or trap them with yellow traps coated with petroleum jelly.

With the summer weather upon us, slugs are having a field day. They eat holes in the leaves of many vegetable, annual, and perennial plants. There are many chemical and non-chemical controls for slugs, including a new one that contains iron phosphate as the active ingredient. The slugs eat the pellets and die, yet the iron phosphate doesn't harm other wildlife or the environment.  There are many other methods to trap them, such as under boards or in wet newspaper rolls in the garden.  The more famous trap is saucers of beer which attract them and in which they drown.  Some gardeners swear by coffee grounds sprinkled around plants.

As your peony blooms fade, snip off the dead blossoms. Removing the dead blossoms will not only make the bush more attractive, it will allow the plant to send more energy to the leaves and roots and less to producing seed.  Spent blossoms also are prone to the gray mold disease which looks just as its name indicates. 

Keep new plantings well watered through the summer. Many new flower varieties you may have purchased in pots like lots of fertilizer.  If you didn’t incorporate a slow release chemical fertilizer into planters, you can “topdress” or sprinkle some on top.  Or use a liquid fertilizer, applied often and according to label directions and amounts.
(Charlie Nardozzi is a nationally known horticulturist, author, gardening consultant, and garden coach (             

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