Pruning basics: tools, cuts and when to prune

Pruning can feel nerve-racking the first time. The good news is that most plants are forgiving, and a few simple rules will get you through nearly every job in the garden. Start small, take your time, and step back often to look at the whole plant.

Why prune at all

You prune to help a plant do what you want it to do. That might be:

• Health: taking out dead, diseased or damaged wood before problems spread.
• Shape: opening up the middle so light and air can get in, which also helps keep fungal disease down.
• Size: keeping a tree low enough to pick and net, or a shrub off the path.
• Fruit and flowers: encouraging the kind of growth that carries the crop.
• Renewal: removing old, tired stems so younger ones can take over.

If you can't name a reason for a cut, don't make it.

The tools

You only need three, and the first one does most of the work.

Choose bypass secateurs, which cut like scissors with two blades sliding past each other. Anvil secateurs, where one blade presses onto a flat plate, tend to crush living stems. They're fine for dead wood.

Keep your tools sharp and clean. A sharp blade makes a clean cut that seals over quickly. A blunt one tears and bruises the bark, which gives disease an easy way in.

Wipe your blades between plants, and especially after cutting anything that looks sick. A cloth with methylated spirits or a household disinfectant does the job. It takes a few seconds and stops you carrying disease from one plant to the next.

A pair of gloves and safety glasses are worth wearing too, particularly when cutting above head height.

The two kinds of cut

Almost every pruning cut is one of two types.

Heading cuts shorten a stem back to a bud. The plant responds by sending out several new shoots just below the cut, so the result is bushier, denser growth. Use heading cuts to thicken up a young plant or to encourage branching.

Thinning cuts remove a whole stem or branch back to where it joins a larger one, or to the ground. They open the plant up without triggering a burst of new shoots. Use thinning cuts to let in light, reduce crowding and lower the height of a tree without making it bushy.

How to make a good cut

1. Find a bud. Look for a bud or small shoot facing the direction you want the new growth to go. On most plants that means an outward-facing bud, so the plant grows out and away from its centre.
2. Cut just above it. Make the cut about 5 mm above the bud. Too close and the bud can dry out; too far and you leave a stub.
3. Angle the cut. Slope it gently away from the bud so water runs off rather than pooling on the bud.
4. Don't leave stubs. A stub of bare stem above a bud, or a stub where a branch used to be, usually dies back and can rot. That rot can move into healthy wood.
5. Don't cut flush either. When removing a whole branch, look for the slightly swollen ring of bark where it joins the trunk or a larger limb. This is the branch collar. Cut just outside it, never into it. The collar is where the tree seals the wound, so cutting it off leaves a bigger wound that heals poorly.

For heavy branches, use three cuts so the weight doesn't tear a strip of bark down the trunk:

1. Make an undercut a little way out from the collar, about a third of the way through.
2. Cut from the top a bit further out, so the branch falls away cleanly.
3. Remove the remaining short stub with a final cut just outside the collar.

The three Ds

Whatever the plant and whatever the season, you can always remove wood that is:

• Dead: dry, brittle, no green under the bark when you scratch it with a fingernail.
• Diseased: cankers, oozing, discoloured bark or dieback. Cut well back into clean wood, wipe your blades afterwards, and put the prunings in the green bin rather than the compost.
• Damaged: snapped, split or rubbing branches. Where two branches cross and rub, take out the weaker or worse-placed one.

Starting with the three Ds is a good way into any pruning job. Once they're gone, it's much easier to see what's left.

When to prune

Timing depends on the kind of plant and on when it flowers or fruits.

There are more detailed guides for fruit trees, citrus and evergreens, and roses and shrubs.

A general caution for our climate: avoid heavy pruning just before a heatwave. Freshly exposed bark and leaves can scorch badly in an Adelaide summer.

How much is too much

A handy rule of thumb is to remove no more than about a third of a plant in one year. Take off much more and many plants react with a flush of soft, leafy shoots (often called water shoots) instead of flowers or fruit, and the plant is stressed while it recovers.

If a plant is badly overgrown, spread the work over two or three years. Take out a few of the oldest stems each time and let the plant rebuild between sessions.

A few final tips

• Stand back after every few cuts. It's easy to get carried away.
• Prune on a dry day where you can. Wet weather helps fungal spores into fresh cuts.
• You don't need to paint or seal ordinary pruning cuts. A clean cut in the right place does the healing.
• If you're unsure about a cut, leave it. You can always take more off later, but you can't put it back.