Grey-leaved plants should be cut back in spring to stop them becoming overgrown and straggly.
Ideally, start pruning them as young plants and every spring thereafter.
Wait until after the last frost and cut back all the shoots to just above the lowest new leaves that are forming.
With old bushes, these should only be cut right back if there are signs of shoots developing at the base of the stem,or you will
risk killing the plant, otherwise restrict pruning them to just shortening last year's growth.