The dormant season, after your shrubs have dropped their leaves, is generally a good time to prune.
However, by pruning during the dormant season, you remove the flower buds of early spring bloomers.
This includes most white-flowered spireas, such as:
> Bridalwreath (Spiraea prunifolia)
> Snowmound spirea (S. nipponica 'Snowmound')
> Vanhoutte spirea (S. Xvanhouttei)
Instead, prune them right after they finish blooming in the spring.
Japanese spirea (S. japonica), which has pink flowers and blooms later, is safe to prune now. This includes varieties such as 'Anthony Waterer', 'Goldflame', and 'Little Princess'.