Deadheading is not necessary for Russian Sage. The best time to cut back Russian Sage is in early spring before new growth emerges. Cut the stems back to about 4 inches above the ground. Some people choose to cut this plant back in the fall, but the stems provide some protection during the winter, along with winter interest, so it's best to leave them in place over the winter. These plants may die back in northern zones but will resprout in the spring.
I can cut back Russian Sage?
Russian Sage grows quickly during the summer and may become floppy. To promote a compact form, cut the plant back by half after blooming. Pruning may also be required if you have yellowed or dead stems; just remove them at ground level.