When to Prune Spring Flowering Shrubs

Many gardeners prune shrubs to remove old or dead branches, to improve the shape of the shrub, to rejuvenate old growth, or even to encourage flowering. Many spring flowering shrubs need to be pruned right after they bloom to prevent loss of flowers for the next year as they bloom on the previous season’s growth. These shrubs need to be pruned immediately after flowering before new growth commences and the new flower buds are formed; otherwise, there is not adequate time for the development of flower buds on the new growth. Spring flowering shrubs can be pruned when the shrubs are dormant during the late winter; however, loss of flower buds will occur if pruned during this period.

Spring flowering shrubs that may be pruned once bloom is completed include lilac, pieris, daphne, azalea, rhododendron, spirea, forsythia, spring flowering viburnum, weigela, flowering quince, red- twigged dogwood, and deutzia.

Pruning lightly is always best. The plant will undergo less stress if pruned frequently and lightly as opposed to pruning extensively less often. It is always good to prune out any weak or dead stems or branches and to cut out any branches that cross over or rub other branches. Weak or dead branches should be cut back to healthy wood or back to ground level. Pruning is very effective in rejuvenating over-grown or neglected shrubs, but it is best to prune back in stages. In the first year, remove about one-third of the oldest limbs to ground level. Then, in the subsequent years, do the same; gradually, the removal of old growth will stimulate the plant and make room for new growth.

Many shrubs need to be rejuvenated by the complete removal of the top of the plant during the dormant season. This results in vigorous specimens that bloom more profusely on new growth. Shrubs that should be cut back to the ground on an annual basis include Caryopteris spp., butterfly bush, crepe myrtle, beautyberry, chaste tree; (Vitex spp.), Gibraltor lespedeza, Russian sage; and smooth hydrangea (Hydrangea arborescens).

Regular pruning improves the shape or look of several types of shrubs. Red-stemmed dogwoods display the red color on the stem on newer wood and need to be rejuvenated on a regular basis for optimum stem color. Smokebush will display leaves the full length of the stem if pruned hard annually and will exhibit more spectacular color and a more pleasing shape. Ornamental willows also display more spectacular stem color if pruned hard annually, especially the ‘Hakuro Nishiki’.

For more information about pruning shrubs, refer to MU Extension Guide Sheet G6870 (http://muextension.missouri.edu/xplor/agguides/hort/g06870.htm).

Mary Kroening, Missouri Master Gardener Coordinator, and UMC Horticulturalist, (573) 882-9633