The Homeowners Column

The Homeowners Column

Pruning Early Flowering Shrubs

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator
slmason@illinois.edu

Forsythias have forced their last flower. Lilacs are in full bloom. Once these early flowering shrubs have flowered, it's time to get out the pruners. Other than being a rite of spring, pruning can promote new plant growth, maintain plant size, encourage flowering, remove diseased or dead limbs and help control insect and disease problems.

However, timing is important, especially when pruning spring blooming shrubs. Early blooming shrubs develop their flower buds during the summer and fall of the previous year. Therefore, as a general rule, shrubs that flower before June 15 should be pruned immediately after flowering. Pruning these shrubs in late summer, fall or early spring will remove the flower buds and therefore the flowers for the season.

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. Heading back or shortening of stems may also be necessary to get shrubs in bounds. Removing old branches can lessen problems from lilac borer, scale and other insects as well as stem diseases.

Shrubs that should be pruned immediately after flowering include lilac, deutzia, kerria, mockorange, weigela, forsythia, arrowwood viburnum, St. johnswort and redtwig and yellowtwig dogwood. Established shrubs of these can also be cut down by the rejuvenation method in February or March. Rejuvenation is the complete cutting of all stems down to 4 to 6 inch stubs.

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. For particularly vigorous plants root pruning with a spade will reduce succulent growth after rejuvenation.

Before pruning, examine the plant thoroughly. If you are new to pruning, tie a colorful ribbon or spray paint the branches to be removed to help you visualize what will be remaining.

Shrub pruning requires a good set of pruning shears or loppers not hedge shears. At each cut of hedge shears, many new growing points are produced making the shrub very dense at the top. The dense growth causes the leaves in the interior of the plants to die.

Hedge shears should only be used on formal hedges. Prune formal hedges to have a keystone shape where the upper branch spread is smaller than the lower branch spread. Hedges pruned incorrectly with perpendicular sides or sides that angle in toward the base will lose the lower leaves. It's not a pretty sight. If a hedge is already in this condition, it can be rejuvenated by cutting back to 6 to 10 inch stubs next spring and then reshape the new growth. If the plants are weak or diseased, plant health should be corrected before rejuvenation. Deciduous shrubs that can be kept as a formal hedge include privet, bush honeysuckle, spirea, pearlbush, ninebark and alpine currant. Deciduous shrubs should not be maintained at a permanent size during the growing season, but allowed to grow an inch or so at each shearing to maintain a good cover of new leaves. Then in February or March, the shrubs can be pruned back to the desired size or smaller.

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