Updated: 30 December at 00:07

The Nelsons

Always an Adventure

Pruning Subshrubs
Don't cut plants like lavender to the ground, and don't touch them in fall or winter
by Debra Knapke


My love affair with lavender and other subshrubs began with my master’s thesis. I spent three years doing my best to kill lavenders and, in the process, became an expert on all things lavender. Since completing my degree, I’ve been asked time and again how to prune lavender and other subshrubs. In one instance, I was asked by a fellow gardener if “renewal pruning” was good for lavenders. I replied that it would probably result in the death of the plant since subshrubs—lavenders in particular—often dislike being cut to the ground. The woman sighed and admitted that her row of lavenders didn’t make it after she cut them back the previous fall.
The reason many gardeners have trouble with pruning subshrubs is because they treat them as they would herbaceous or woody plants. Herbaceous plants can be lightly pruned during the growing season to encourage new growth and be cut back to the ground in fall to tidy things up once the plants go dormant. Most maintenance and cosmetic pruning for woody plants is done in late winter (with a few minor touchups or deadheading during the growing season) to minimize plant stress and to encourage new growth and branches.
What is a subshrub?

When it comes to subshrubs, however, it’s a good idea not to cut them back to the ground since this can result in the removal of their growing points and can ultimately lead to their demise. Similarly, the worst time to prune is during the cool (or potentially fluctuating) temperatures of fall and winter. The tender new growth induced by pruning is likely to be damaged or killed when cold winter temperatures arrive. The loss of the energy expended on the new growth can exhaust the plant, causing it to lose its vigor or die. Depending on the type of subshrub, the best times to prune are in the spring and, in some cases, after the first bloom. During the cooler seasons, limit your pruning to the removal of spent blossoms and dead branches and avoid cutting into live woody stems.
As for all pruning, it is important to know your plant. Learn its life cycle: When does it initiate growth in the spring? When does it bloom? When does it rest? Just remember that if you make a mistake—like pruning off all the flowers or cutting too much off and killing your plant—there is always next year to experiment again.

All photos, except where noted: Jennifer Benner. Illustrations: Melissa Lucas.
From
Fine Gardening 102 , pp. 42-45