Troubleshooting
Spiraea 'Grefsheim' problems — and how to fix them
Spiraea 'Grefsheim' (Spiraea x cinerea 'Grefsheim') is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Late frost damage to flowers
Flowers open early in spring and are vulnerable to hard late frosts. Site in a position sheltered from cold north and east winds.
Overly large habit
Can reach 1.8 m and spread equally wide. Allow sufficient room at planting. Prune only immediately after flowering to control size without sacrificing next year's buds.
Poor flowering after incorrect pruning
Grefsheim blooms on old wood from the previous year. Pruning in autumn, winter, or early spring removes the flower buds; prune only after the spring bloom finishes.
Aphids
Soft spring growth can attract colonies of aphids. Treat with insecticidal soap or encourage natural predators such as lacewings and ladybirds.
Powdery mildew in late summer
Occasional in hot, dry conditions. Water consistently at the root zone and thin congested older stems to improve air circulation.
Prevent spiraea 'grefsheim' problems before they start
Most spiraea 'grefsheim' issues are care-mismatch, not bad luck. Dial in the basics:
Spiraea 'Grefsheim' problems — FAQ
Why is my spiraea 'grefsheim' late frost damage to flowers?
Flowers open early in spring and are vulnerable to hard late frosts. Site in a position sheltered from cold north and east winds.
Why is my spiraea 'grefsheim' overly large habit?
Can reach 1.8 m and spread equally wide. Allow sufficient room at planting. Prune only immediately after flowering to control size without sacrificing next year's buds.
Why is my spiraea 'grefsheim' poor flowering after incorrect pruning?
Grefsheim blooms on old wood from the previous year. Pruning in autumn, winter, or early spring removes the flower buds; prune only after the spring bloom finishes.
Why is my spiraea 'grefsheim' aphids?
Soft spring growth can attract colonies of aphids. Treat with insecticidal soap or encourage natural predators such as lacewings and ladybirds.
Why is my spiraea 'grefsheim' powdery mildew in late summer?
Occasional in hot, dry conditions. Water consistently at the root zone and thin congested older stems to improve air circulation.