Three ways to prune spirea
Sometimes it’s hard to make the cut, but pruning spirea is a pretty worry-free job. You won’t kill a spirea by pruning it! (At the worst, it might not bloom for a year). I have three easy ways to prune them, as well as the best time of year to do it. Check out the steps and helpful illustrations below, and you’ll be good to go.
1. Prune spirea to encourage a rebloom
To get more flowers later into summer, snip off the spent heads as they fade. If you have only a few to cut, scissors or snips are fine. Got a lot to do? Use hedge shears. It won’t matter where you make the cuts, just remove as many flower heads as you can. This technique works with astilbe, bigleaf hydrangea, hosta and Japanese spirea. It won't work with garland spirea.
2. Prune to make tight mounds
If you like a dense, structured look, prune just as new leaves start to show in spring. Use hedge clippers to shear off no more than half of the top growth. You’ll get a tight, habit with more, but smaller, flower clusters.
3. Prune spirea to get big flower clusters
Spirea that’s not pruned or pruned to the ground each spring has a casual, loose habit. In early spring, before the leaf buds start to swell, cut all of the stems down so they’re 4 to 6 in. tall. You can use pruning shears and cut one at a time or hedge clippers and simply cut them all off at once — it makes no difference. In a few weeks, new growth will sprout, creating a full dense plant that will be about half to two-thirds its full height with lots of flowering stems.