When should I prune shrubs and trees?

Prune before the buds break, not after — early spring while the plant is still dormant. Once you see green tips or leaves, stop. For overgrown shrubs like lilac or forsythia, do renewal pruning in late winter. For trees, prune dead or crossing branches while bare, but skip oaks until late fall to avoid oak wilt. If you missed the window, wait until after flowering or next dormant season.