I had beautiful rose bushes for several years and this year they contracted black spot. I tried many things but nothing worked. I removed the plants as there was hardly anything but the canes left anyway. Should I do anything to the soil to prepare for new bushes? Since it’s now mid-Sept should I wait until next spring to plant new bushes, in hopes the ground will freeze and kill any remnants of the disease?
Unfortunately, freezing weather does not kill black spot spores. It is vital to remove every bit of rose material from the bed. Some sources say to remove mulch as well. Make sure the roses are in full sun and are spaced far enough apart so they don't touch; good air circulation is the most important prevention measure. To improve air movement don't plant roses against a wall; prune every year to keep the plant open in the center; and remove the lowest leaves on the canes. When conditions are ripe for infection - cool, humid nights - be vigilant and remove leaves showing signs of disease promptly. If a stem has a black spot or blister, remove it by cutting 8-10 inches below the spot. Use drip irrigation only via an installed system or soaker hoses on low. Fall is a good time to plant roses.