Black spot first shows up as dark spots on rose leaves, black or deep brown, sometimes with a purplish tint. They usually start on the lower leaves, the ones closest to the ground, where rain and splash can carry fungal spores from the soil. Over time, these spots grow, sometimes merging into larger blotches that cause the leaves to turn yellow. When this happens, the leaves drop off, and your rose loses a significant portion of its leaf area, which it needs to capture sunlight and produce food.
The disease overwinters and hides away in fallen leaves and on old stems, waiting patiently for spring. When the weather warms up, especially in damp conditions, the fungus wakes up and infects new growth. It spreads through wind, water, and even on your gardening tools if you’re not careful. With this in mind, the gardening experts at David Austin Roses have shared what “the best medicine” is for keeping black spot at bay — prevention.
The pros said: “Prevention is the best medicine. First, try to water your roses only at the base. Wet leaves provide a perfect landing pad for spores to germinate and infect.
“If you have to water overhead, perhaps because of your garden’s setup, do it early in the day so the leaves dry quickly in the sun.”
In addition to watering, good nutrition is also important. Feeding your roses with a balanced, slow-release fertiliser keeps them strong throughout the season. A well-fed rose is a resilient rose.
When black spot does make an appearance, remove the affected leaves and prune out any infected stems.
It is crucial to be thorough in collecting fallen leaves and old debris; don’t toss them into your compost heap, as that just allows the fungus to return to your plants next season. Instead, bag them or add them to the green waste bin.
With winter in full swing, now is the perfect time to prune roses. This allows the plant to improve air circulation. A lack of air circulation can contribute to black spot.
After pruning, a good layer of mulch helps suppress any spores lingering in the soil and maintains steady moisture levels.
Compost, leaf mould, or organic soil improvers work well here. Aim for around two inches deep.
