Overgrown shrubs, rejuvenation pruning is the answer

Deciduous shrubs, such as forsythia, flowering cherries, viburnum, lilacs, hydrangeas, dogwoods, and others, sometimes become overgrown. If you don’t prune them each year, they may get straggly over time. Rejuvenation pruning encourages new growth and gives the plant a new start.

As these plants age, they may have unproductive or dead branches, gangly stems, and overall unsightliness. Or perhaps they have outgrown the space.

Normal pruning practices, such as those mentioned last week, would have you remove no more than one-third of the branches at a time. However, on shrubs, you can use rejuvenation pruning to improve the appearance of the plant.

It’s simple to rejuvenate a deciduous plant. Cut all the branches back to about six inches above the ground. That’s it. New growth emerges, and the plant starts to take shape again.

The most important factor in successful rejuvenative pruning is to do it in the late winter or early spring, before new growth emerges.

Deciduous shrubs store their food in the roots over the winter. In the spring, this stored food is put into new growth for the plant. Therefore, this pruning method should be done before the stored sugars are spent.

I usually do this on a few of my summer-blooming hydrangeas. They set flower buds on new growth, so I am not cutting off the upcoming season’s flowers.

I also do this on my red-twig dogwoods, as they tend to get a disease that causes the branches to turn brown. Since I want the red branches, I cut all the old branches off, and the new growth isn’t affected (at least for the first few years).

You can also rejuvenate overgrown deciduous shrubs by removing one-third of the older branches each spring, finishing over the course of three years. I prefer cutting everything instead of waiting that long.

Evergreen shrubs such as boxwood, taxus, and juniper should not be rejuvenated using this method. They store their sugars in the foliage over the winter. Therefore, if you cut them back using this method, it will take several years before they fill back in.

It doesn’t mean you can’t do it, but realize that the plant doesn’t have foliage for photosynthesis and thus sugars necessary for plant growth. They will continue to grow and push out new growth, but it takes longer.

With evergreen shrubs, the farther back you cut on the branches, the longer they take to recover. Again, it can be done, but the foliage won’t recover as quickly as a deciduous shrub.

Next week, I’ll discuss pruning fruit trees.