Q: We have Spirea Golden Princess that are growing rather large. How hard could/should I trim them when they are finished flowering for the season? I do trim/deadhead when the fisrt blossoms die.
Best to prune them after the first round of flowering. Shearing to shape will encourage rebloom. If you choose to shorten them you may do so. I'd do that in late winter or very early spring. Happy Yardening, Nancy