Pruning, and when not to

Most pruning disappointment comes from cutting at the wrong time rather than from cutting badly, and the timing follows one principle.

The principle

Prune flowering shrubs after they flower.

Which sounds obvious and resolves nearly everything.

Plants that flower in spring and early summer generally formed those buds during the previous summer, on old wood.

Cutting them in winter or early spring removes the flowers before they open.

Plants that flower in mid to late summer generally flower on growth made in the same year, which means they can be cut back in late winter or early spring without loss.

Where you do not know which a plant is, observing when it flowers gives the answer.

Why prune at all

The legitimate reasons, in order.

Removing dead, damaged and diseased material, which can be done at any time of year and which is the only pruning many plants need.

Removing crossing branches that rub and create wounds.

Improving airflow through a congested centre, which reduces fungal problems.

Controlling size and shape, where a plant has outgrown its position.

Encouraging flowering or fruiting, for the specific plants where this applies.

Renovating a neglected plant, which is a longer project.

Pruning for no reason is common and generally harmful, since every cut is a wound.

How to cut

The technique.

Cut just above a bud or a side shoot facing the direction you want growth to go, generally outward.

Cut at a slight angle away from the bud so water runs off.

Do not leave a long stub, which dies back, and do not cut so close that the bud is damaged.

For larger branches, cut back to the branch collar — the slight swelling where it meets the trunk — rather than flush, since the collar contains the tissue that seals the wound.

Use sharp clean tools, since crushed and torn cuts heal poorly.

Wound paints and sealants are no longer recommended by most authorities, since trees seal wounds themselves and sealants can trap moisture.

The plants people get wrong

Hydrangeas, where the common types differ.

Mophead and lacecap types flower on old wood and should be pruned lightly after flowering, with old flowerheads left over winter for frost protection and removed in spring.

Paniculate and smooth types flower on new wood and can be cut back hard in late winter.

Lavender, which should be trimmed after flowering and never cut back into old bare wood, from which it will not regrow.

Roses, where the type determines the approach and where the general principle is to remove dead and crossing wood and prune to an outward-facing bud in late winter for most types.

Clematis, which is divided into groups pruned differently depending on when they flower.

Fruit trees, where winter pruning encourages growth and summer pruning restricts it, which is used deliberately.

The timing constraints beyond the plant

Worth knowing.

Nesting birds are legally protected in many jurisdictions, which restricts cutting hedges and shrubs during the nesting season — generally spring and early summer.

Checking before cutting anything substantial is both a legal and a practical requirement.

Frost is a consideration: pruning in autumn stimulates growth that is then damaged, which is why late winter is preferred for many plants.

And some trees bleed sap heavily if cut in late winter or spring, which for birch, maple and walnut means pruning in summer or autumn instead.

When not to prune

Situations where restraint is better.

A newly planted shrub, which needs to establish.

A plant that is doing what you want.

Anything you cannot identify, until you have observed it for a year.

And anything large enough that the work involves a ladder or a chainsaw, which is a professional matter and where the injury statistics are substantial.

General information only, not professional advice. Check local wildlife protection rules before cutting hedges and shrubs, and use a qualified tree surgeon for substantial tree work.