Friday, June 6, 2008

Landscape - Pruning Spring Flowering Shrubs

A common question this time of year by landscapers is when to prune spring flowering shrubs. The following is some information on the subject.

Early blooming shrubs develop their flower buds during the summer and fall of the previous year. This is often called "blooming on old wood." Therefore as a general rule, shrubs that flower before June 15 should be pruned soon after flowering. Pruning these shrubs in late summer, fall or early spring will remove the flower buds and therefore the flowers.

Spring flowering shrubs are generally pruned by the renewal method. Each spring after flowering, prune out the largest stems to the ground to stimulate new growth from the crown and remaining stems. Remaining stems can then be shortened to shape.

Shrubs that should be pruned this spring soon after flowering include lilac, deutzia, kerria, mockorange, weigela, forsythia, viburnum, St. johnswort and redtwig and yellowtwig dogwood.

Shrubs that bloom after June 15 can be pruned in early spring. Summer and fall flowering shrubs bloom on new wood or stems that were produced in the same season as flowering. Many of these shrubs can be pruned by the scary rejuvenation method. Rejuvenation is the complete cutting of all stems down to 4 to 6 inch stubs generally done in February and March.
Rejuvenation is used when multistemmed plants become too large with too many stems to justify saving any one to two year old growth. In other words, the shrub is a tangled mess of stems.

However, don't wait too late in the year for rejuvenation pruning. To be cautious large old shrubs should not be rejuvenated in late spring or summer. With the early flowering shrubs that need rejuvenation, you may decide to just sacrifice the flowers one season and prune them to the ground in late winter. The following respond well to rejuvenation pruning: abelia, honeysuckle, beautybush, snowberry, slender deutzia and privet.

Adapted from "Time to Prune Spring Flowering Shrubs" by Sandra Mason, Educator, Horticulture & Environment, University of Illinois Extension.

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