When should I prune a shrub?

The timing rule that resolves most confusion is about when the shrub sets its flower buds, because pruning at the wrong moment removes the flowers before they open.

Shrubs that flower in spring generally do so on wood grown the previous year. Those buds are already present through winter, so a winter tidy-up removes the display. Prune these immediately after flowering, which gives them the rest of the season to produce next year's wood.

Shrubs that flower in mid or late summer generally do so on the current season's growth. These can be pruned in late winter or early spring while dormant, and the resulting new shoots will carry the flowers. Pruning hard at that point often improves the display.

When you do not know which category a shrub falls into, the observation is simple: note when it flowers, and prune shortly afterwards. That rule is correct often enough to rely on.

Three exceptions apply year-round. Dead, diseased and damaged wood should be removed whenever noticed, since there is no benefit to leaving it. Crossing branches that rub can be taken out at the same time.

Avoid pruning in late summer and early autumn generally, because it stimulates soft new growth that will not harden before frost.

A few species have specific requirements worth checking individually. Some, including certain maples and birches, bleed sap heavily if cut in late winter and are better pruned in summer. Others flower on both old and new wood, which makes them forgiving.

Check for nesting birds before any substantial cutting in spring and early summer, which is a legal requirement in many places as well as good practice.