University of Vermont
Department of Plant and Soil Science

gmg logoSummer News Articleline


Leonard Perry, UVM Horticulturist
and Charlie Nardozzi, Garden Consultant

Proper weed trimming, pruning lilacs, and preventing cucumber beetles are some of the gardening activities for this month.

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.

After lilacs finish flowering, you can “deadhead” or prune off the old blossoms. I haven’t noticed leaving this significantly affects future flowering, and birds love the seeds they produce later in the season.

To reduce the height of tall lilacs, prune the old stems to the ground and allow new suckers to grow and flower.  This is drastic and will reduce the height all at once, but it will take several years for the plant to look attractive again.  This also won’t work on the many lilacs that are grafted or budded.  This means the desirable cultivar (cultivated variety) is growing on a vigorous understock or roots.  Prune the tops off, and this less desired cultivar will take over.  What was a red lilac may then become purple, or an early lilac may become a late species.

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 soon after bloom of the previous year.

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” (until blooms begin to open—by then the adult beetles should be moved on), spray pyrethrum botanical spray, or trap them with yellow traps coated with petroleum jelly.

Keep new plantings well-watered throughout 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 (synthetic or organic), applied often and according to label directions and amounts.

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. 

Peonies are hardy, easy care, long lasting perennials with gorgeous blooms.  If you’re looking for one, check out ‘Mahogany’.  This Japanese type peony gets 28- to 36-inches high, with shiny dark red petals which contrast nicely with the yellow central stamens.  The single, cup-shaped flowers bloom early to mid-season, and make good cut flowers.  It has been around since 1937, when it was bred by Lyman Glasscock.  In 2015 ‘Mahogany’ won a gold medal from the American Peony Society, and was chosen by them as the 2016 Peony of the Year.

(Charlie Nardozzi is a nationally known horticulturist, author, gardening consultant, and garden coach;

Return to Perry's Perennial Pages, Articles