Posted: 24/05/2017 at 12:24
The aim is to provoke the plant into producing new growth from low down which will make a strong new structure for what will become a three, four, or even five foot tall shrub. Yes, it's tricky when the new growths shoot from high on the stems like that, but you prune it to shape, removing quite a bit of the flowered growth and the plant will react accordingly. Don't be frightened about pruning out too much. It's a spiraea, you won't kill it.