Prune some shrubs now and others later

With spring just around the corner it is time to begin some of those long awaited outdoor pruning chores.   Shrub pruning is just one outdoor job that is often done just before growth begins in the spring, but not all shrubs should be pruned in late winter-especially if a spring flower show is desired.  Here are a few tips to help guide your shrub pruning efforts this spring.

Deciduous shrubs fit into three groups: shrubs that flower in the spring on wood produced last year (old wood), shrubs that flower in summer on current season’s growth (new wood), and shrubs that are grown for foliage rather than flowers.

Spring Flowering Shrubs

Spring flowering shrubs (shrubs that flower before June 1^st) should not be pruned until immediately after flowering.  Pruning earlier will not harm the plant’s health, but the flowering display will be greatly reduced.  Many of the flower buds will be cut off with the trimming before they have bloomed.  Examples of these spring flowering shrub types include forsythia, lilac, quince, mock orange, serviceberry, and viburnum.

In some cases spring flowering shrubs get too large and must be cut back hard.  If this is the case then they should be pruned back in late winter even though the flower show will be lost.  Waiting until after flowering to do a hard renovation pruning can cause more stress to the plant. 

Summer/Fall flowering Shrubs

Shrubs that bloom in the summer/fall (after June 1^st) are best pruned now (late winter) before the flower buds are produced on this year’s new growth.   Examples include caryopteris, shrub roses, pyracantha, rose of Sharon, spirea, butterfly bush, vitex, crepe myrtle, and more.

There are three basic methods used in pruning shrubs: thinning, heading back and rejuvenating.

Thinning is used to eliminate branches from a shrub that is too dense. The objective is to cut one-third of the oldest stems to the ground each year, which in turn stimulates new (flowering) growth from the base of the shrub.  This is done in the spring before growth starts.

Heading back is done by removing the end of a branch by cutting it back to a bud.  This type of cut is used for either reducing height or keeping a shrub to a compact size.  Cut back to a healthy bud pointing outward/upward if possible.

Rejuvenation is the most severe type of pruning and may be used on multi-stem shrubs that have become too large and have too many old branches to justify saving the younger canes. Every stem on the plant is cut back to a 5- to 6-inch stub. This is not recommended for all shrubs but it does work well for many including lilac, dogwood, privet, rose of Sharon, elderberry, honeysuckle, spirea, forsythia, pyracantha, ninebark, little leaf mock orange, shrub roses and flowering quince.  Note that with rejuvenation pruning there may be no or reduced flowers on some plants for up to two years. 

On a final note remember that evergreen shrubs cannot be rejuvenation pruned and typically differ in their pruning requirements from deciduous shrubs.  Many evergreen shrubs do not regrow like deciduous plants and have different pruning requirements and  methods.