Aside from pruning the plant, black spot is one of the biggest challenges you will face with growing roses. The disease is caused by a fungus which infects the leaves. It can happen all year round, and the telltale signs are enlarging purplish or black patches which appear on the leaf’s surface. The area around the spots may turn yellow and brown too, with the leaves eventually dropping off. Obviously, this all massively inhibits the health of the rose.
It was last autumn when I spotted my garden roses heavily infected by black spot disease. The majority of the leaves on the plants were covered in the disease, and many of them had fallen onto the soil near some of my other plants. Before I could prevent black spot from infecting more of the leaves, I had to deal with the damaged ones first.
The first step in curing my roses was to remove all of the diseased leaves, and there were a lot of them. To do so, I used a clean pair of secateurs and snipped them off.
I like to clean the secateurs by running a 70% alcohol wipe over them. I also made sure to clean them between cuts to prevent the further spread of the disease.
For those who don’t have a pair of secateurs to hand, simply pulling off the leaves by hand will suffice.
After stripping the leaves, I gathered them all up, the ones that had dropped too, and chucked them in the garden waste bin. Never add them to your compost bin, as this will spread the disease to plants your compost is being used on.
The next step has been the most important part of keeping my roses free from black spot, and that’s to apply mulch to the base of the plant. I first did this in autumn, then reapplied it again in the winter and spring.
Mulch gives the roses a nutritional boost, keeps weeds at bay and helps retain moisture for them.
However, it’s also particularly helpful to roses which suffer from black spot. That’s because it prevents rain from splashing the spores in the soil onto the new growth.
There are lots of things you can use as a mulch. Good quality garden compost, straw, bark, or well-rotted manure. I opted for garden compost as I have heaps of the homemade stuff I make from fruit and vegetable scraps, eggshells and grass clippings.
The key is applying it right. Spread a one to two-inch layer around the base, keeping a small gap around the stems to prevent rot.
The only drawback I find to using compost is that it decomposes quickly, so you’ll need to refresh it a couple of times a year – once every season will be fine.
Another tip I’ve gathered from keeping my roses black spot-free is about watering. Water your roses at the base of the plants, not the leaves.
Ideally, water first thing in the morning, so that the warmth of the day will prevent a damp atmosphere from forming around your rose, as a damp atmosphere is the environment within which the spores will thrive and spread.