Now’s the time to repot and prune semi-woody shrubs
DEAR GARDEN COACH >> Can I prune my perennials, like salvias and penstemons? What about other semi-woody shrubs like California native sages and a shrub called cream bush? We cut off the brown flowers in August. What about repotting plants at this time of year? — Joan DeMarco
DEAR JOAN >> I am often asked this question from late summer into early autumn. The Chinese refer to this time of year as the fifth season, or the time to transition from active to reflective. In the garden I refer to it as the “transformational season” since light and weather begin fluctuating before settling into the season in the wheel of the year.
While temperatures still warm up in the afternoon, the days are shortening, and the sun is shifting. The decreased light signals plants and animals that change is coming. And at this time of year for animals it means to fatten up, while for plants it signals the time to journey inward.
I usually lightly prune plants like non-native salvias and penstemons throughout the growing season to prolong blooms. I allow the seed heads to stay on native sages until this time of year, since the birds like the seed. At the pollinator garden in Walnut Creek, we began pruning the natives sages, and shrubs like Holodiscus discolor (cream bush) in late September, so you can prune dead or diseased branches now.
I like to open the center of Holodiscus by removing some of the older branches — these are more grayish in color, while new wood is a deeper brown. I do this because it lets more light and air into the center, which encourages new growth next spring. Holodiscus does not require any hard pruning other than what you already have done by removing the spent flowers.
During the fall I prune non-native salvias and penstemons by one-third to one-half their size. I wait until late February to do a major pruning, especially of salvias, because in my area many are frosttender. If you prune now, they have a chance to put on a little more growth that protects the plant during a winter freeze.
In California, horticulturalists refer to autumn as a second spring because it is the best time for planting. As the light fades, air temperatures begin to dip, but the soil is still warm. These conditions are best for new plants since root growth develops with warm soils, followed by winter rains, giving plants time to settle in without the stress of hot days. This is true for repotting plants, as well. I begin this process in early September and am amazed at how happy the plants seem immediately.
One thing to consider as we transition into the dormant period: Reduce or stop fertilizing potted plants until late February, when the days get longer. Native plants do not like fertilizer, and those such as salvia and penstemons need a rest. Cut them back, give them a nice top dressing of compost, and they will settle in and be quite happy until spring.
Lastly, I always recommend researching what your plants need, including the best time for pruning or fertilizing. When caring for plants properly, you eliminate stress; like humans, plants are less likely to get diseases or other problems when they are healthy.