I have not grown that variety of spirea myself but other cultivars of Spiraea x bumalda do respond by producing another flush of buds after trimming back. I grew 'Magic Carpet' in my old garden because I liked the range of foliage color it offered and its compact size. But I detested the rank pink flowers. Every time the plant would bud up to bloom, I'd shear off all the flower buds and was rewarded with a flush of new, brightly colored foliage growth, followed in a couple of weeks by new flower buds. I went through this process several times during the summer months. I only trimmed back the top inch or two of the plant....just enough to remove all the flower buds completely.

I have that variety. I often gather each bush up in a "ponytail" and cut off the dried blooms and another inch or two of growth, depending on how much it will take to have them look neat again. I usually save big trims for the fall.

Most Spiraeas do well with a "bowl haircut" treatment. With your shears in good, sharp condition, round them over, cutting as much as 1/2 of stem length off the entire plant, in a rounded form. Along with this, do occasional "renewal prunings" which consist of removing oldest, thickest stems, as near to ground level as possible. Doing these two things in concert, one should be able to maintain a planting almost indefinitely.

+oM