The general rule is the colder the climate, the later you prune in winter.
At the Dunedin Botanic Garden, we prune modern roses in late July, when they are at their most dormant and hopefully the heaviest of frosts have passed.
Pruning, at its simplest, is the removal of old, weak, spindly growth and the shortening of flowering stems, to encourage new growth. It opens up the centre of the bush, to allow more light and air movement.
How to prune roses
• Use clean sharp tools.
• Choose a dry day, with some air movement.
• Remove the 3Ds - dead, diseased and damaged stems - cutting off cleanly at the base or a suitable outward-facing bud.
• To open the bush, remove inward-facing growth and side shoots.
• Select and retain five to seven healthy canes evenly spread around the base and shorten by half to one-third.
• Make cuts on a 45-degree angle, sloping away from the bud.
• Carefully scrub around the base afterwards with a wire brush to remove any moss and old bark; this stimulates desirable new growth from the base.
• Clean your tools after cutting diseased wood, and between bushes to prevent spread of diseases.
• After pruning, apply a spray of copper and oil at winter strength. Spray around bud union to destroy overwintering diseases and insect eggs that tend to hide at the base.
Check it out
A rose-pruning demonstration will be held on Saturday, July 19, at 1.30pm. Meet at the rose garden or in the information centre if it is raining.
- Linda Hellyer is curator of the rose garden at Dunedin Botanic Garden.
