Carolyn, 

Thank you for your question. 

I feel your pain. I had this very same issue last year. I had to dig and dig to remove all of the root ball that I could. I completely re-landscaped the entire area. This season I go out almost daily and pluck the young Russian sage sprouts from the ground. A lot of work. 

Here is what Marisa Y. Thompson, PhD, Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center writes:

"The Russian sage plant has beautiful flowers and, as you have stated, they have the unfortunate characteristic of spreading vigorously. There are several things you can try to limit its unruly growth.

Contact herbicides are one option. These are herbicides that kill only the part of the plant to which they are applied. Unlike translocated (systemic) herbicides, they will not move through the plant killing other parts of that plant. You can apply this to the unwanted sprouts. However, these sprouts will regrow below the point at which the herbicide was active.

Another consideration is reducing the water they receive. Russian sage plants will grow large when well irrigated. If the irrigation is limited, the plant will not grow as large, but will still produce flowers. Fertilizer, especially nitrogen fertilizer, will encourage growth. Limit the nitrogen fertilizer that you give the plant. Phosphorus is more important for flowering, so choose a high-phosphorus fertilizer that contains little or no nitrogen (read the label for this information). Super phosphate and colloidal phosphate should provide what you need. Bonemeal is not a good source of phosphate in our calcareous soils.

You can also consider managing the spread of your Russian sage by planting it in an area that allows it to grow and become a large clump. It is also possible to contain the Russian sage by surrounding it with very competitive plants. I saw Russian sage growing in its native habitat in Uzbekistan. The plants were not large and sprawling because the grasses growing around them competed with the Russian sage plants and kept the Russian sage from growing vigorously. In my garden I have planted chocolate flower and Mexican hat plants around my Russian sage. These plants compete with the Russian sage for water and nutrients. In this manner they effectively reduce the growth of the Russian sage. These competitive plants don't spread by underground runners (rhizomes), so they are easier to control. However, the competitors may need to be pruned back when they spread out of bounds. The seedlings of the competitive plants must also be removed. Planting Russian sage with other competing plants may require a large space, but is attractive and each plant's size is kept in check by the other plants."

Hope this helps. Good Luck!

Kindly, 

Kerry P

Colorado Master Gardener, El Paso County