Pruning roses, hedges, natives and soft shrubs

Shrubs vary a lot in how they like to be pruned. Some, like roses, thrive on a hard cut each year. Others, like many natives and lavender, sulk or die if you cut into old wood. This guide walks through the common ones in Adelaide gardens.

For tools and how to make a clean cut, see the guide to pruning basics.

What to prune when

Roses

In Adelaide, rose pruning is a July job, when the plants are dormant. Pruning then means fresh growth arrives as the weather warms, with flowers from late spring.

How to prune a bush rose

1. Remove the three Ds. Cut out dead, diseased and damaged canes first.
2. Take out old canes. Remove one or two of the oldest, greyest canes right at the base. They flower less and crowd the bush.
3. Clear the centre. Remove thin, weak and crossing canes so the bush is open, like a vase. Good airflow helps keep black spot and powdery mildew down.
4. Shorten what's left. Cut the remaining strong canes back by about half to two thirds, to an outward-facing bud, with a sloping cut about 5 mm above it.
5. Clean up. Rake up old leaves and prunings and put them in the green bin. They can carry fungal spores into next season.

Climbing roses are different. Keep their long main canes and train them along a fence or frame, then shorten the side shoots that flowered back to two or three buds.

Deadheading in season

Through spring, summer and autumn, snip off spent flowers. Cut back to a leaf or bud below the old bloom. This tidies the plant and encourages repeat-flowering roses to keep going. In late autumn, stop deadheading so the plant can slow down before winter.

Hedges

A good hedge is the result of many light trims rather than one big chop.

• Trim little and often through the growing season, roughly spring to early autumn.
• Shape it slightly wider at the base than the top. This lets sun reach the lower leaves, so the bottom doesn't go bare.
• Start young. Trim a new hedge lightly from the start to make it bushy all the way down.
• Avoid trimming in a heatwave. Freshly cut leaves underneath are soft and scorch easily.
• Check for nesting birds in spring before you start.

Native hedges like westringia (coast rosemary) and lilly pilly respond well to regular trimming.

Native shrubs

Most Australian native shrubs like a light tip-prune straight after flowering. Pinch or snip off the last few centimetres of each stem, just behind the spent flowers. This keeps plants compact and bushy, encourages more flowers next season and stops them getting leggy.

The big caution: many natives won't reshoot from old, bare wood. If you cut a branch back past the leaves to brown, leafless stem, it may never regrow. Always cut back into the green, leafy part of the stem.

• Grevilleas: tip-prune after flowering. Many grevilleas don't regrow well from old wood, so avoid hard cuts. Some people react to grevillea sap and leaves, so gloves and long sleeves are a good idea.
• Bottlebrush (callistemon): cut off spent flower spikes just behind the flowers before they turn into woody seed capsules. Bottlebrush handles harder pruning better than most natives and can often be cut back to renew an old plant.
• Correas, westringia and emu bushes: light trims after flowering keep them dense.
• Banksias: remove spent cones if you like, but prune lightly and stay within the leafy growth.

If a native shrub has become leggy and woody, it's often better to replace it than to try a hard renovation.

Salvias

Salvias are tough and flower for months. Different types need slightly different care, but these rules work for most garden salvias:

• Through the flowering season, trim off finished flower spikes to encourage more.
• Shrubby salvias benefit from a firmer cut back at the end of the season. Cut back to just above healthy new shoots or leaf buds.
• Herbaceous salvias that die back can be cut down to near ground level once new growth appears at the base.

Lavender

Lavender wants regular light trims and hates being cut hard.

1. After the main flush of flowers, trim off the spent flower stems and a few centimetres of the leafy growth below them.
2. Shape the plant into a soft mound.
3. Never cut into old, leafless wood. Lavender rarely reshoots from bare stems, and a hard cut can kill it or leave a permanent bald patch.

The same light-touch approach suits other woody herbs like rosemary and sage. Trim them after flowering, staying within the leafy growth.

A note on timing in our climate

Adelaide summers are hot and dry. Avoid big pruning jobs just before a heatwave, and water shrubs well before and after any significant prune. Late winter and spring pruning gives plants the mild weather they need to recover.