University of Vermont
Department of Plant and Soil Science
PRUNING AND OTHER JUNE GARDENING TIPS
Leonard Perry, UVM Horticulturist
and Charlie Nardozzi, Garden Consultant
Cutting back early-blooming perennials, pruning rhododendrons and
spring-flowering shrubs, and watching for lily-leaf beetles are some of the
garden activities for this month.
Many early-blooming perennials including nepeta, veronica, delphiniums, and
some perennial salvias such as 'May Night' will rebloom if you cut off the
faded flowers. For bushy plants like nepeta and veronica and salvia,
shearing with hedge trimmers is the easiest method.
The best time to prune rhododendrons, to improve their flowering next year,
is right after they finish blooming. The best pruning tool to use is your
hand. The dried flower clusters will snap off when you bend them, just be
careful not to break off the tiny buds just below the old flowers, which are
the future blooms for next year.
Now is the time to prune those spring-flowering shrubs too, right after
bloom, such as forsythia and lilacs. Although these can be cut back to
near the ground, they will take several years to regain a dense shrubby
appearance. If such drastic pruning isn’t needed, remove about
one-third of the oldest branches. To reduce height, cut back remaining
shoots by one-half to one-third, less if desired. This will make
plants more bushy.
Bright red lily-leaf beetles are easy to spot on lily leaves. If you
only have a few, you can pinch them between your fingers or knock them into
a can of soapy water. The larvae usually feed on the undersides of the
leaves, and they have a slug-like body covered with their black excrement
(ugh). You might want to don gloves when squishing them. Neem spray also is
effective against the larvae, with repeated sprays effective in killing
Iron phosphate granules, sprinkled around plants, are an effective, nontoxic
pesticide for slugs and snails. (Brand names include Escar-Go and Sluggo.)
Coffee grounds and liquid coffee are also effective -- the higher the
caffeine, the better.
If you have a strawberry bed, harvest frequently and remove any berries that
show signs of gray mold or rot diseases. These berries not only are
inedible, they quickly spread the diseases to other ripening fruits. Pick
and remove the rotten berries. Mulch under plants with straw to reduce
contact with the ground where the disease spores reside.
Apple trees are notorious for setting more fruit than they can support.
Usually the tree relieves this burden by dropping some young fruit in what's
called the "June drop," but you may have to thin in addition to this natural
drop. Try to leave six inches between fruits so they can develop to their
full size and sweetness.
Set your tomato supports in place before plants get too large. Smaller
determinate (bush) varieties can be supported with small cages, but larger
indeterminate varieties (those that keep growing like a vine) need large
cages or tall stakes. Secure cages with stakes so they don't topple.
Remove some of the side shoots or “suckers”, particularly on the
indeterminate varieties, to get larger fruit sooner.
Other gardening activities for this month include keeping bird baths filled
and cleaned regularly, visiting local perennial growers to see what is in
bloom and might add early color to your garden, mowing lawns often but not
too low (3 to 4-inches high is best), and making sure if weed-trimming to
stay away from tree trunks. Make sure mulch isn’t piled around trunks too.
(Charlie Nardozzi is a nationally known
horticulturist, author, gardening consultant, and garden coach;
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