I pruned my summer blooming Spirea (Magic Carpet) 2 weeks ago. Attached is a photo of what it looked like on April 19. There is new leaf growth at the base but the taller branches look rather sparse. My question is whether i should prune it down to 6 inches from the ground now or is it too late in the season?
Thank you for contacting Toronto Master Gardeners.
You are right to have pruned your Magic carpet spirea (Spiraea japonica ‘Walbuma’) in the early spring as it is a shrub that blooms on new wood and should therefore be pruned in late winter or early spring while it is dormant and before new growth appears.
In general, pruning to maintain the shape of a shrub entails taking out the oldest, largest stems which will not produce as many blooms by cutting them to the ground. This will encourage new stems to grow and the shrub will benefit from more light and air. Each year approximately one-third of the stems can be removed this way.
It looks from your photograph that you took out some old branches and tried to keep the shape of the shrub. It is a bit difficult to tell from your photo, but the new growth could be starting where you cut out old branches. Growth should appear further up the plant as the weather warms up. Later in the season after the shrub blooms, you can lightly shear your shrub to tidy it up and potentially encourage reblooming.
Spirea can take heavy pruning, but for your plant with new growth appearing at its base, this may be best left to next season. This would be beneficial if the shrub is severely overgrown which may not be the case for your plant.
This article has some good tips on pruning shrubs:
Toronto Master Gardeners has a Gardening Guide on Deciduous shrubs that has some general information on the care and maintenance of these plants. You can find it here:
April 21, 2021