Pruning is the garden job people put off longest and get wrong most often, and nearly every mistake comes down to timing rather than technique. This guide covers why to prune, the few tools you need, the three kinds of cut, when to prune by what the plant does, the rule that costs Australian gardeners the most natives, and the four cuts that are always safe to make.
Why prune
Pruning removes dead, damaged and diseased wood, opens a plant so air and light reach the centre, keeps it to the size the space allows, and directs its energy where you want it: into flowers and fruit on fruit trees, into density on a hedge, into a clean trunk on a tree. It is also the answer to one of the most common complaints we hear, and our article on why your plant is not blooming puts pruning near the top of the list. Taken to its logical end, the same principle produces the flat, trained forms in our guide to espaliered trees.
Tools
Three tools cover almost everything: bypass secateurs for stems up to finger thickness, loppers for anything up to about 40 mm, and a pruning saw for the rest. Hedge shears are for hedges only. Keep the blades sharp, because a clean cut seals and a crushed one rots, and wipe them with methylated spirits between plants when cutting out diseased wood. Gloves and eye protection are not optional: several common Australian garden plants have irritant sap, euphorbia and firesticks can cause serious eye injury, and frangipani, cunjevoi and star jasmine all irritate skin.
Pruning techniques for beginners
Heading cuts
A heading cut shortens a stem to a bud or a side shoot. Growth then comes from the buds just below the cut, so heading makes a plant denser and bushier. It is the cut for hedges, for tip pruning young natives and for shaping a shrub. If you grow cut flowers, Bloom and Root Floral's guide to pinching plants explains when to pinch and which cut flowers thrive on it.
Thinning cuts
A thinning cut removes an entire stem right back to its point of origin, at the main branch or at ground level. Nothing regrows from the cut point, so thinning opens a plant up, improves airflow and light penetration through the canopy, and keeps the natural shape. This is the cut for a congested fruit tree or a shrub that has become a solid ball of twigs.
Reduction cuts
A reduction cut shortens a branch back to a side branch at least a third as thick, so the side branch takes over as the new leader. It is how you bring a tree or large shrub down in size without the dense regrowth that heading would cause. Most good pruning is a mix: thin first to open the structure, then head back selectively where you want density. Getting this balance right is what our guides to pruning lilly pilly for a hedge and pruning magnolias for the best bloom apply to two very different plants.
The three-cut method for larger branches
Any branch too heavy to hold with one hand should come off in three cuts, or its own weight will tear a strip of bark down the trunk as it falls. First, make an undercut on the underside of the branch, roughly 20 to 30 cm out from the trunk, going about a third of the way through. Second, make a top cut a little further out again and let the branch fall; the undercut stops the tear. Third, remove the remaining stub with a clean cut just outside the branch collar, the slightly swollen ring where the branch meets the trunk. Leaving that collar intact is what allows the wound to seal.
When to prune, by what the plant does
Almost every pruning mistake comes from timing. The rule is simple once you know which category a plant falls into.
| Flowers on | Prune | Examples in Australian gardens |
|---|---|---|
| Old wood (last season's growth) | Straight after flowering | Camellia, gardenia, tibouchina, wattle, star jasmine, Cascade lilly pilly |
| New wood (this season's growth) | Late winter | Crepe myrtle, hibiscus, bougainvillea, roses |
| Both, needs two cuts | Summer and winter | Wisteria |
Prune an old-wood plant in winter and you cut off the flowers you were waiting for. That single error accounts for most "my healthy plant never blooms" complaints. For deciduous fruit trees and most deciduous ornamentals, late winter, just before bud burst, is the standard time; for evergreen hedges, a light trim after each flush of growth through the warm months.
The Australian native rule
This is the one that costs people established plants. Many Australian natives will not reshoot from bare old wood: cut past the green growth into the brown interior and the gap is permanent.
- Tip prune lightly and often, from a young age, taking only soft growth.
- Never cut into bare wood on grevillea, leptospermum, westringia or most conifers.
- Callistemon is the forgiving exception; it reshoots readily from old wood.
- A native that has gone woody and leggy is usually better replaced than rescued.
Lilly pilly, murraya, viburnum and photinia all reshoot readily, so those can be cut back hard in spring and retrained.
Do not prune before a heatwave
Specifically Australian advice. Fresh cuts and newly exposed inner foliage scorch badly in extreme heat, so check the forecast before a major prune in summer. Similarly, avoid pruning in wet weather in humid Brisbane and Sydney conditions, since it spreads fungal spores between plants.
Four cuts that are always right
- Dead wood: any time, on anything.
- Damaged or diseased wood: cut back to healthy tissue, disinfecting tools between cuts.
- Crossing and rubbing branches: remove one of the pair.
- Inward-growing branches: open the centre for airflow, which matters a great deal in humid Australian climates.
Technique and the common mistakes
Cut back to a branch collar or just above an outward-facing bud, at a slight angle. Do not leave stubs, which die back and invite decay, and do not cut flush into the trunk, which removes the collar the tree needs to seal the wound. Do not seal cuts with paint or tar; it traps moisture and pathogens against the wound, and clean cuts left open heal better. Never remove more than about a quarter of a plant's foliage in one go, because the leaves are what feed the recovery. Check council rules before touching a large tree: across Australia, trees above a certain height or trunk circumference are protected, and pruning or removing one without a permit can carry substantial fines. Anything requiring a ladder or work above head height near power lines is a job for an arborist, not a beginner.
When you are ready to apply all of this to a boundary planting, our guide on how to create a great hedge and keep it looking sharp takes it from the first trim through to a mature, dense screen.
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