Garden Tips: Keep spring flowering shrubs blooming with pruning

Marianne C. Ophardt, WSU Benton County ExtensionMay 16, 2014 

ATHOME-SAGE 4 MCT

Forsythia sage is a fall blooming salvia that hummingbirds relish. (Norm Winter/MCT)

HANDOUT — MCT

Last weekend, I took advantage of the weather to prune my forsythia that was crowding plants. I hadn't pruned it much for the past two years, and it was becoming unruly. It put on a beautiful show of blooms this spring, but I knew that if I didn't remove some of the old wood, it probably would not have as many flowers next year.

My approach was to remove one-third to one-fourth of the older (thickest stems with side shoots) stems down to the ground. A healthy forsythia is a vigorous shrub that sends up new stems each year that bloom the following spring. Removal of the oldest stems should be done after flowering because the buds for next spring are formed on the new wood by early summer. Pruning later in the season or in winter will reduce the flower display the following year.

A weigela was one of the plants being crowded by the forsythia. I planted it in early summer two years ago, and initially it benefitted from the shade the forsythia provided, but now it needs more light. I also have two mature weigela shrubs elsewhere in my landscape.

One of these weigelas is Wine and Roses, with dark burgundy leaves and dark pink flowers. It has prospered, but now it has become bedraggled, and there are dead twigs and branches throughout. Since weigelas are prone to winter dieback, this may have been caused by the cold snap last fall. The dieback could also be related to the increasing amount of shade provided by two trees on that side of the yard. Weigelas do best in full sun and will become straggly if planted in shade or crowded by other plants.

Perhaps I should remove it and plant a more shade tolerant shrub, but I think I will see if I can revitalize it first. As soon as it is finished blooming, I will prune out the thickest, oldest stems along with any of dead branches and twigs. To shape it, I will prune back any overly long stems to a side branch, being sure not to remove more than one-third of the stem.

Most other multistemmed spring-flowering deciduous shrubs are also pruned after flowering. This is because they too flower on wood produced the previous growing season. These shrubs include forsythia, weigela, lilac, viburnum, honeysuckle, mock orange, Nanking cherry, flowering quince, white-flowered spireas, beautybush and deutzia.

Also, don't forget to deadhead the spent flowers or seed-heads from the stems you don't remove. This will give the shrub a tidier appearance and allow its energy to go into plant growth rather than seed development.

-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

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