The Russian sage plants our landscaper put in about five years ago are a problem. There are three of them, thriving and beautiful, but they put out a great many suckers and are hard and messy to pull up.
I used to trim the originals back in the fall, then thought maybe I was causing them to spread, so I left them scraggly looking all last winter, only to find them carrying on as usual.
Is there some way to keep them in their place?
Russian sage seems to be a bit of a Jekyll and Hyde sort of plant. A few people I've talked to don't seem to have problems with the suckering, but most of you "lucky" ones have plants that are too aggressive for their own good.
Whether you cut them back or not has no bearing on if they sucker. I don't have an easy answer for you. One situation that seems to prevent the problem from occurring is to plant Russian sage in a dry, xeric area with a drip emitter or two near the plant. This tends to limit the plant to the irrigated area.
It doesn't always work, but most plants in this sort of situation seem to better behave themselves.
Another way to keep a Russian sage in-bounds is to plant it inside of a "sleeve" that prevents underground runners (they're called rhizomes) from spreading out.
You can use a plastic nursery pot and cut the bottom out. I'd use a pretty good-sized one, say, 14–20 inches in diameter. Bury it up to the brim and place the Russian sage in the middle.
This restricts the roots a bit so the plant doesn't get as big and vigorous, but it will contain those rhizomes.
You really don't want to start spraying herbicides. The effective ones have systemic activity and will end up damaging or killing the mother plant.
Using contact type weed killers isn't much of an option, either. They won't hurt the mother plant, but you have to continue to spray as long as you have the plant and besides, these herbicides really don't work all that well on a semi-woody plant like Russian sage.
There is a product called Sucker Punch that slows suckering of problem plants such as this. You cut the suckers off and spray the product on the freshly cut ends. It keeps the plant from suckering in that area.
You'll have to do it every year, but at least it will buy you some relief from those pesky suckers!
The only other option is to continue to do what you've been doing all along: digging out the suckers.
As you've mentioned, it is hard and messy work and many people eventually just dig the plant out and eliminate it altogether.