University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article

SUMMER IN THE PERENNIAL GARDEN

Dr. Leonard Perry, Extension Professor, and
Andrea Luchini, Graduate Assistant
 

Most the time spent in the northern perennial garden during summer is with maintenance, visiting perennial nurseries, and planting new perennials.

During dry periods, you may need to water flower beds.  This is especially true for first year perennials, and annual flowers.  Most established perennials can survive some drought, except for those such as astilbe, snakeroot, primrose, or lungwort that need moist soils.  Beds that are covered in mulch, without trees (these take up most the soil water), and with moisture retentive soils high in organic matter will need water less often. Unless you get about one inch of rain per week, you may need to water such plants in these conditions.  It is best to water thoroughly, and do so less often, than watering lightly more often.

Weeding, dead-heading, and de-leafing are good tasks to do throughout the summer.  Weeds should be dealt with before they go to flower and to seed.  Most can be pulled easily or cut with a hoe, but some need to be dug out with a trowel, dandelion digger, or similar tool to get the root.

Dead-heading-- removing spent flowers-- is important not only for aesthetic reasons, but also may extend bloom.  Examples of these types of perennials include yarrow, bellflower, Shasta daisy, bee balm, and foamflower.  When dead-heading perennials, a general rule of thumb is to prune back to the next bud, leaf, or flower.  For some plants such as peach-leaved bellflower, this will mean removing single flowers from a flower stalk.  For others such as coneflower, it will mean removing a long stem.  You may want to be especially quick to deadhead those that self-sow, such as members of the mallow family (hollyhock and it's relatives).

De-leafing is done for aesthetic reasons, and to maintain a disease-free garden. Dead, decaying matter is a prime location for diseases such as gray mold, rots, and leaf diseases to begin.  This process is simply removing dead leaves from your perennial plants, often from the ground as with lungwort, coralbells, or heartleaf saxifrage, or from outer edges of a clump as with daylilies. If these don't pull off easily, use pruners or scissors.

Some plants can be pruned in early summer to maintain them at a shorter height and so they donít require staking.  Some examples of these include asters, bellflower, Joe Pye weed, Helen's flower, tall garden phlox, and speedwell. These plants should be pruned well before they produce flower buds.  If you only prune some of the plant, or one or two plants, you can get a staggered bloom effect.  As a rule, plants can often be cut back by half.

There are also some perennials that grow best when they are cut back after flowering.  Perennial geraniums, lady's mantle, bleeding heart, and catmint will often begin to grow
new foliage in the center of older, straggly foliage.  If you see this, cut back the old foliage, leaving the smaller new foliage.  Youíll have a new second plant develop for the rest of the summer.

Throughout the summer, you should be checking at least weekly for insect pests in your garden. Not all insects are pests, so itís a good idea to know what you are looking at before deciding if you have a problem.  Keep in mind that many insects serve as food for birds and even for other beneficial insects.  Chemical controls may kill off predator and beneficial insects as well, resulting in your pests coming back in even greater numbers!

In mid summer, perennial plants may like an additional shot of fertilizer, especially if you use a faster-acting chemical fertilizer (organic fertilizers tend to be slow-release, but you can get slow-release chemical fertilizers as well).  Don't over-fertilize, as you may get all leaves and no flowers.  Perennials often tolerate low fertility.

Plan time to visit local gardens and perennial nurseries to get ideas, see what is in bloom, and find new plants for your own garden.  Perennials can be planted throughout the summer.  Just make sure you keep them well-watered until established, especially if dry and hot periods.


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