You can, but it might be better to wait until spring. If you want the quick answer, here’s a 90-second video on cutting back Russian sage in fall. Read on if you’d like a deeper explanation.
Keep in mind it doesn’t need to be cut down in fall. There is absolutely not a problem in Colorado with putting this task off until spring. (How often do you hear it’s okay to put something off? Embrace it!)
However, here are some of the special cases where you can consider cutting it back in fall:
Prevent new seedlings. If you have a problem with Russian sage seedlings spreading around your yard, you can reduce the amount of new seed by cutting off the old flowering stalk part of the stem. I find this is a problem when Russian sage is planted in rock mulch. Rarely do I find it when it’s planted in wood mulch.
Keep in mind Russian sage also spreads by underground runners, so cutting off the old flowering stalks won’t totally contain the spreading problem. But, it can help. Cut each stem right above a set of leaves, then shape the plant for symmetry.
You’re going to be busy in spring. Getting all of your landscape tasks done in spring can be a lot of work in a short period of time. Some people like to spread the work out over the year by doing what they can in fall.
If this is your situation, I’d recommend cutting off the upper two-thirds of growth in fall, which you can learn about here. This method also works well for people who are out of town until mid-summer since they’re not around for spring cleanup.
It looks really bad. During rainy summers, Russian sage can get very floppy. By the time fall arrives, it looks pretty terrible. I like to cut floppy Russian sage back in the fall after the leaves go dormant since it’s not adding any ornamental value to the landscape at that point.
But what about years when it’s still growing upright by fall? One of Russian sage’s downsides is its winter appearance is not so great. It looks like a bunch of grey-brown leafless stalks. It can be tempting to tidy it up by cutting it back somehow. The problem is that cutting something that doesn’t look that great in the first place often doesn’t make it look that much better.
Notice the Russian sage in the photo was cut back in fall. Rather than looking great after pruning, it looks like a ball of grey-brown stems with a few leaves hanging on. Not much of an improvement.
One way to make Russian sage look better is to simply surround it with landscape plants that have a better appearance in winter. That way, your eye is drawn to the beautiful plants and hardly notices the Russian sage.
Evergreen trees and shrubs, like pines and spruces, are great companion plants. Ornamental grasses work well, too. That way, you get the benefit of the beautiful flowers of Russian sage in summer plus the winter interest of surrounding plants in the off-season.
Nonetheless, if your Russian sage looks terrible go ahead and cut it back. Sometimes it gets flattened by a heavy snowstorm. Or, it might be floppy from too much shade or water. In those cases, it often makes sense to cut the plant to ground level and let it regrow in spring.
Why spring instead of fall?
There are two main reasons I like to cut back Russian sage in spring in Colorado. First, we never really know how far it’s going to die back over the winter. Sometimes we have a mild winter and it dies back a little, but sometimes we have a harsh winter and it dies back a lot. Waiting until spring allows you to see how much actually died back so you know which method to use and where to cut. You might find this video helpful to see my favorite approaches.
Second, some plants are less likely to survive the winter if you cut them back in fall. Russian sage is such a tough plant its not likely to die unless you live at a very harsh, exposed site. However, if you leave the stems standing over the winter, leaves will collect around the base of the plant. The leaves can act like an insulation layer to protect the crown and roots. Sometimes, any bit of insurance is helpful.
All in all, cut back Russian sage in fall if you have to, but in most cases it’s better to wait until spring.