Will try this for my roses this year: A tonic for black spot and powdery mildew on roses Roses, while beautiful, are often plagued with black spot or powdery mildew. I mix these ingredients into a tonic, which I spray on my roses: 2 teaspoons of baking soda and 1/2 teaspoon of liquid soap or Murphy's oil soap in 2 quarts of water. The tonic protects the roses for months.
Full rose bushes with lots of flowers? Use Epsom salt. Produces more & larger blossoms & helps grow new canes from base of plant. Feed Epsom salts to roses at time of planting, & again at first sign of new growth. Feed once more when flowers are in full bloom. It is almost impossible to use too much Epsom salt. It is pH neutral - won’t harm your soil. Breaks down into water, magnesium, & sulfur, all beneficial to most plants.