Question:

I have questions about several plants that I am growing. How and when should I prune Spanish broom and Russian sage? Mine are huge and need to be trimmed. When I prune them, can I take cuttings and start new plants? I have grown catmint for a year and want to know how to care for it.
- Paula R.
   Roswell, NM

Answer:

Spanish broom and Russian sage should be pruned during the dormant season if large stems are removed. As you have observed, the Spanish broom becomes quite large and is often not given a large enough planting site. This makes pruning a necessity as it exceeds the space allotted to it.

The Russian sage can also become large but with restricted irrigation, its growth will also be restricted. However, it may die back in the winter and pruning to remove dead or week branches may be necessary.

The best method to prune each of these is often called "rejuvenation" pruning. In this manner of pruning, some or all of the old, large stems are removed near the ground level. This leaves only smaller, newer branches and encourages development of new growth from the base of the plant. The newer branches tend to flower more heavily than the older stems, so this increases flower production by the plant in addition to reducing its size.

If you prune these shrubs in the manner that you prune trees and other shrubs (cutting stems back only partially), you will often see the shrub produce a cluster of new branches near the end of the stem you pruned. It forms a broom-like growth at the end of this stem. This broom growth often dies back after a few years. Rejuvenation pruning is a better way to prune these and other shrubs that respond in the same manner.

It is probably best to prune only a few of the oldest, largest stems from the center of the Spanish broom. All stems of the Russian sage and the catmint may be pruned back to almost ground level. They will produce new growth from the base of the plant in the spring.

Regarding propagating the plants from the stems removed during pruning, I doubt that the Spanish broom will produce new plants for you. However, Russian sage and catmint may grow roots from the cut stems if the cut base is treated with rooting hormones and the plants are kept in a greenhouse or other humid location while the roots form. Cuttings from Russian sage will probably be more successful in producing roots if you use cuttings taken in early summer (called softwood cuttings) rather than winter-pruned stems.

Spanish broom, Russian sage, and catmint may also be propagated from root cuttings. Root cuttings are fairly large roots (diameter of a pencil) dug from near the base of the shrub and placed in a prepared soil. If kept moist, they may produce new plants. This is something to do in the late winter or early spring.

As far as culture of the catmint, this is a plant that prefers a well-drained (sandy) soil and can be killed by excess water or a soil that remains too moist. Do not over-fertilize or over-amend the soil with organic matter. If you don't like the appearance of the flower spikes that remain after flowering, you can remove these flower spikes in the summer. You may be rewarded with renewed flowering if you do this. Like its relative, catnip, it is attractive to cats that will come to roll in the planting. Plant it far from other plants that may be damaged by visits from cats.

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.

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