Issue: January 20, 2001

• Pruning Spanish broom?
• Fertilizer for deicing?

Pruning Spanish broom?

My Spanish broom plant has become extremely large and is interfering with my driveway. Can I prune it? How? When?

This is a common problem. Spanish broom grows much larger than the space often allotted to it. You can prune it. I often see it pruned by shearing or just cutting back. When the Spanish broom is pruned in this manner, it produces a "broom" type regrowth at the point where it was cut. In time this regrowth often dies or declines and look unattractive.

Rejuvenation pruning is a better way to prune Spanish broom. Rejuvenation pruning is accomplished by pruning one or a few of the main stems to within a few inches of the ground. This should be done before growth begins in the spring.

The plant will respond by producing new stems from the base instead of the "broom" at the end of a pruned branch. These rejuvenated stems will bloom prolifically as they mature.

You do not need to cut all the branches in a single year; instead, go through a three-or-four-year cycle of removing the oldest stems, a few each year. At the end of the cycle, you will be ready to remove those which re-grew after the process began, starting the cycle again. This is a good way to keep the plant size appropriate for the space allotted to it.

By the way, rejuvenation pruning is a good way to prune several commons shrubs. Lilacs and Forsythia also benefit from rejuvenation pruning but should not be pruned until later in the spring following their blossoming period. A number of plants used in xeriscape plantings can also be rejuvenated. These include fernbush, chamisa, and other shrubs that produce multiple stems at the base.

When planting shrubs, avoid size problems by choosing plants that fit the available space. Before buying the plant, learn how large it will become when mature.

Fertilizer for deicing?

A neighbor used fertilizer to melt ice on his sidewalk. He said that this is better than de-icing salt because it won't hurt the plants. Is this true?

Fertilizer isn't labeled for use as a de-icing salt, and though some will function in this manner, they will not be as effective as products made for de-icing. Regarding the reduced damage to plants, your neighbor is partially correct. Some de-icing salts can be harmful to the landscape. There are others, however, that are less harmful to the landscape yet manufactured for the purpose of de-icing. Fertilizer will be less damaging than the first of the two types of de-icing salt, but fertilizer can cause some damage if the fertilizer salts accumulate to an excessively high concentration in the landscape near the sidewalk. These salts can be diluted by irrigation, but if there is poor drainage, some damage may appear in the landscape.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!