Answer: The absolute best time to prune burning bushes is in the winter or early spring - just as new growth is beginning. If you prune them back now in mid-summer, they will put out new growth, but the leaves may not mature enough to produce that spectacular fall color that burning bush's are capable of producing.
If your shrubs are quite over-grown, you may want to reduce their size in increments so you won't totally shock the plants. Remove one-third of the live growth now; one-third next spring, and one-third next summer. Removing more at any one time can cause real stress to your shrubs.
Best wishes with your landscape!
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