Gardening column: Pruning shrubs | Columnists

Do your shrubs need a facelift?

If they’re old and tired, if their flowers are lackluster, there’s a way to bring back vitality without replacing them with new shrubs.

Rejuvenation pruning, also called renewal pruning, is the botanical fountain of youth. It’s a method that stimulates vigorous growth and more flowers. It’s a drastic approach that doesn’t require horticultural expertise, just a pair of pruners. Simply cut all the stems 6 to 12 inches above ground. In a couple of months, you’ll have a brand-new shrub.

Before you get to chopping, there are some considerations. This technique is effective on most shrubs, in particular multistem shrubs such as abelia, nandina and oleander. There are exceptions such as rosemary, especially when it’s old and leggy, that won’t recover from rejuvenation pruning. Also avoid pruning conifers, which are cone-bearing plants, with this technique. They do not possess latent buds. This includes plants like junipers and cryptomeria. Renewal pruning a conifer will turn it into a stump.

Don’t rejuvenate trees, even small ones. Anything with a single trunk will be permanently altered. Crape myrtles and chaste trees will probably grow back, but it’s probably not a look you’ll enjoy.

Where you make the cuts is not as critical on shrubs as it is on trees. Random cuts, or heading cuts, can be made anywhere to stimulate adventitious growth along the stem. It will result in a dense, proliferation of new growth. This is what we want on a shrub, especially if it has gotten leggy.

Timing is important. You’ll want to avoid rejuvenation pruning in late fall to winter. New growth can be wiped out by a cold snap. Wait until March, after the frost-free date, to prune. Spring is an ideal time, just before bud break, to get vigorous growth. Summer pruning will work on most shrubs, just irrigate to avoid drought during recovery.

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You will have to consider flowers. Most shrubs set flower buds on the previous year’s growth, or old wood. These are typically spring flowering shrubs, such as azaleas, viburnum and hollies. If azaleas are pruned in winter, the flower buds will be removed. Red berry-like fruit from hollies will be reduced with fewer flowers. The shrubs will recover, but the flowers will be sporadic. No worries, the flowers will be back the following year.

If you don’t mind losing flowers for the season, then renewal prune whenever is appropriate. To preserve flowers on old-wood flowering shrubs, prune shortly after blooms are spent. Azaleas can be pruned until the end of June without risking flower bud removal.

Oleander shrub

This oleander shrub was 10 feet tall and leggy. It was cut back to 24 inches in winter. A cold snap killed all the new growth, but it recovered in the spring. Tony Bertauski/Provided

There are shrubs that bloom on current-season growth, or new wood, such as oleander, butterfly bush, abelia and hibiscus. Crape myrtles are also in this category. These are summer blooming plants. Pruning in late winter or spring can stimulate new growth and more flowers.

There are also shrubs that bloom on both old and new growth, such as some roses, Encore azaleas and some hydrangeas. How do you know what wood, old or new, your plants are blooming on? A Google search can solve most of your questions. “Does loropetalum bloom on old wood” will get you an answer.

If you can’t identify the shrub, there’s an app for that. Picture This or Plant Snap will identify plants from a photo. In my experience, these apps get the identification correct a high percentage of the time.

If rejuvenation pruning is too radical and you don’t want to wait for bare stems to recover, then consider thinning. Don’t wait until the shrub is overgrown. It’s best applied when the shrub is about ideal size or just a little beyond. Select about a third of the branches with hand pruners. This method takes a little finesse to maintain the natural form while reducing the size.

Sharing is the last option, although this is a personal preference. Unless you have a formal landscape, geometric shrubs such as squares and spheres lose the natural appeal of a landscape.

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