Today’s date is April 27. I live in Toronto. Is it too late in the Spring to prune back a well established spirea shrub to 6”? I don’t want to prune it so hard to not have growth and flowers. I plan to prune the dead flowers from the top and thin the shrub somewhat but there is a fair bit of new growth so I am hesitant to prune too much. Full sun, loam soil, water once a week with when there is no rain. May I kindly ask your advice for the best route to take with this pruning job.
Thank you so much for your time.
Thank you for contacting Toronto Master Gardeners.
Spiraea japonica ‘Anthony Waterer’ flowers on new wood, meaning the young shoots emerging now will produce this year’s flowers. Generally, cutting the entire shrub back to 6” or so would be recommended in late winter to early spring, before new growth emerges.
However, it is not too late for some less aggressive pruning of your shrub for cosmetic purposes. Removal of last year’s flower heads, in particular, will not affect the plant’s ability to flower this year. It should be just fine to prune a considerable amount of the old wood if you would like to thin or otherwise shape the shrub, as long as you mostly avoid the areas where new growth is emerging. Given that your shrub is well established, pruning even a few portions of new shoots would probably not impair the plant’s ability to grow and flower this year; it is really up to you how you would like to strike the balance between thinning the shrub (if you feel it is necessary) and maximizing the density of flowers this year.