Fall-winter cleanup: Pruning your woody subshrubs

Unlike herbaceous perennial plants that die back to the ground each winter, subshrubs maintain a woody framework of branches from which new growth emerges in spring.

These basically, are small shrubs. The spent flowering growth needs pruning each year. Some, like lavender or rosemary, are evergreen, while others, such as bluebeard (Caryopteris incana), are semi-dormant in winter and just a mass of woody stems. The hummingbird favorite, Salvia greggii, is an evergreen subshrub and maintains a framework of woody branches from which new flowers grow in spring. Bush thymes are small subshrubs.

Subshrubs are hardworking plants in the garden, their woody structure giving them year-round presence. They often flower profusely during the growing season, and can be used in a variety of different ways in the garden, grouped together or combined with herbaceous perennials. As they develop permanent branches they don’t appreciate dense foliage of other plants lying on them.

Each of these subshrubs grows and should be pruned differently. They should not be cut to or near the ground like herbaceous perennials, as they may not resprout from the old wood that develops over time.

Lavender can be a real sculptural feature in the garden even when not in bloom, if it is pruned correctly. Its compact rounded forms can give great interest in the winter landscape. The best time to prune lavender is after blooms are spent. Shear off spent blooms, cutting stems down into the foliage, not above it.

If lavender is not pruned a couple of inches down into the foliage each year, it gets larger and more open in growth, and often develops ‘cracks’ in the foliage as this effect progresses. This takes away from the neat appearance many of us desire. If you are able to shear the plant in summer to a neat ball, it should need just a quick trim in winter to even it up. If you miss the summer pruning, prune lavenders when the worst of the winter cold is finished.

There are a few exceptions to this pruning regime. French lavender (Lavandula dentata) is one of the most floriferous of the lavenders and may flower year round in warmer areas. It has a more open and irregular growth habit. Pruning should just consist of pruning off any unsightly branches or stems. Spanish lavender also does not need any pruning, although some shear the plants after spring bloom. These two varieties are long lived.

The variety ‘Goodwin Creek Gray’, a French lavender cross, needs cutting back hard in our wet winter climate as the fuzzy gray foliage molds in rainy weather. Its growth can be cut back by about a foot in winter. It is best in drier climates like the Central Valley.

Rosemary comes in many varieties - from 1 to 6 feet, weeping or completely prostrate. Rosemary can be left unpruned, or can be sheared after the main bloom is past. The very prostrate variety “Irene” may not need any pruning. If the plants are untidy, they can be pruned to neaten them up anytime.

Bluebeard (Caryopteris incana) looks like a bunch of dead stems right now. The spent flowering stems should be pruned back into the portion of the stem where you will see new, small leaves forming, just above a bud. The plant will develop a rounded shrub-like structure over time, to about 3 feet. Bluebeard has light to mid-blue blooms that bees and butterflies love and that complement its silvery leaves.

Salvia greggii is a widely grown plant. The main flower color is crimson, but there are a number of cultivars with flower colors from white, pale yellow to pink. Salvia greggii is different than the also popular Salvia microphylla ‘Hot Lips.’ This Salvia benefits from being cut back to about 8 to 10 inches. Salvia greggii forms a woody structure. Maintain the structure of the plant, and just trim off the flowering stems in winter. There are many good crosses between Salvia microphylla and S. gregii. Most are pruned in between the two pruning types. Watch for where the new growth comes from - the top or the bottom of the plant - and prune accordingly.

Bushy thymes are short-lived plants. They look their best for only two to three years. The spent blooms should be sheared off after bloom has ended, and foliage trimmed by about one third in winter.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at: katebfrey@gmail.com, freygardens.com or on Twitter @katebfrey