Pruning basics: when, how and how much

First rule: when does the plant flower?

This governs all the timing. A plant that flowers on the current season's growth — bougainvillea, oleander — is pruned in late winter or early spring before growth starts. One that flowers on last season's growth, like jasmine, is pruned immediately after it finishes flowering. Prune the second type in spring and you have cut off the branches that were about to bloom.

Never take more than a third

Don't remove more than a third of the plant in a single cut. A plant balances its roots against its foliage, and taking more than that at once shocks it into throwing long, weak shoots called water sprouts — weaker than the branches you removed, and unproductive. If a tree genuinely needs heavy reduction, spread it over two or three seasons.

What comes off first, always

Start with these four before any cosmetic shaping — you will often find that removing them is all that was needed:

• Dead and dried wood
• Damaged or diseased branches
• Crossing branches that rub and wound each other's bark
• Water sprouts and suckers from the trunk base or below the graft union

Tools: sharp and clean

Blunt secateurs crush tissue instead of cutting it, and a crushed wound heals more slowly and lets fungi in. More important still: disinfect tools between trees, especially after cutting diseased wood — unsterilised secateurs are one of the fastest ways to move a disease around a garden.

When not to prune

Avoid pruning at the height of summer: the plant is already heat-stressed, cuts open wounds at the worst time for healing, and stripping foliage exposes inner branches to direct sun they are not adapted to, which scorches them. Avoid it just before a hard cold spell too, since the new growth pruning triggers is highly frost-sensitive.