When should I prune a tree in my garden?

Pruning timing is not arbitrary tradition. It follows from two things: when the plant sets the buds that will become next year's flowers, and when the pathogens that infect fresh cuts are active. Once you know which of those governs a particular tree, the correct month follows, and you can work it out for a species nobody has told you about.

What you'll need

• Sharp secateurs, loppers and a pruning saw
• Disinfectant for tools (optional)

Step by step

1. Check whether the tree is protected before you cut anything.A Tree Preservation Order covers pruning, lopping and topping, not just felling, and Conservation Area rules require notice. Ring the council first. This applies to a light tidy-up as much as to a reduction.
2. Take the default position: dormant season for most deciduous trees.November to February, when the tree is leafless, the structure is visible, there is no sap pressure and most pathogens are inactive. Apples, pears, hawthorn, hornbeam, oak, most ornamental trees.
3. Never prune stone fruit in winter.Plums, damsons, cherries, gages, apricots, peaches and ornamental prunus must be pruned between late spring and midsummer, when they are growing actively. Winter pruning invites silver leaf and bacterial canker, both of which enter through wounds and can kill the tree.
4. Avoid late-winter pruning on bleeders.Birch, maple including acers, walnut, vines and hornbeam bleed sap heavily if cut as the sap rises in late winter and early spring. Prune them in late summer to early autumn, or in the depths of winter well before the sap moves.
5. Prune spring-flowering trees straight after flowering.If the tree flowers before about midsummer, it flowers on wood made the previous year. Pruning it in winter cuts off the flowers. Prune within a few weeks of the flowers finishing, giving the tree the whole season to make next year's wood.
6. Prune summer-flowering trees and shrubs in late winter.If it flowers from midsummer onwards, it flowers on growth made that same season, so cutting back before growth starts is correct and often produces better flowers.
7. Remove dead, damaged and diseased wood at any time of year.This is always correct, needs no seasonal justification, and should be the first thing done on any tree before deciding what else to remove. Diseased material should be taken well back into sound wood.
8. Prune evergreens in mid to late spring.Once the risk of hard frost has passed and they are about to grow. Cutting evergreens in autumn leaves wounds exposed through winter with no growth to close them.
9. Prune lightly and regularly rather than hard and rarely.A tree pruned a little each year keeps its shape and never needs a traumatic reduction. The single biggest cause of ruined garden trees is fifteen years of neglect followed by a drastic cut.
10. Check for nesting birds and bats, every time.Nests in use are protected, and cavities, splits and loose bark in mature trees are potential bat roosts, which are strictly protected whether or not bats are in them at the time. Both checks come before the saw.
11. Know where the job stops being yours.Anything requiring a chainsaw, work above head height, or a branch over a building, road or wire is a job for a qualified arborist with insurance. Chainsaw use requires training, certification and full PPE, and should never be attempted up a ladder or in a tree by a householder.

Tips

• Write the species and the month on a label or in a garden notebook the first time you look it up. The question recurs annually and the answer does not change.
• The rule 'prune after flowering' handles most ornamentals correctly without knowing anything about the species, because it automatically respects where the buds are set.
• Never prune in a hard frost. The tissue around the cut is damaged and dies back further than you intended.

Common mistakes

• Pruning a plum or cherry in winter — Silver leaf spores are abundant in the cooler months and enter through fresh wounds. It is the classic way to lose a plum tree, and it is entirely avoidable by pruning in June instead.
• Winter-pruning a spring-flowering tree — The flower buds for spring were set last summer on that wood. Cutting it off in January removes the entire display.
• Cutting a birch or acer in February — Sap is rising and the tree will bleed for weeks. It rarely kills a tree but it weakens it and looks alarming.
• Using a wound sealant — Sealants trap moisture and can encourage decay. Current practice is a clean cut just outside the branch collar and nothing else — the tree seals its own wounds.

Questions people ask