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A lot depends on when your spirea blooms. If it blooms in the spring, you want to prune it right after it blooms. If it is a summer blooming spirea, then prune the spirea in winter or early spring. I have included several publications to help you in deciding what type it is and how to prune it.

https://hgic.clemson.edu/factsheet/spirea/#:~:text=After%20flowering%20has%20finished%2C%20prune%20the%20mostly%20spring-blooming,less%20severe%20pruning%20than%20other%20species%20of%20spireas.

https://extension.umn.edu/planting-and-growing-guides/pruning-trees-and-shrubs

https://extension.unh.edu/resource/basics-pruning-trees-and-shrubs-fact-sheet

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