QuestionsHow to growRosesWeeds, Pests and DiseasesRose Mildew 0 Vote Up Vote Down Ita Ryan asked 6 years ago I have 2 roses in a half barrel facing south. One is Dorothy Perkins and covered in mildew. It is growing slowly I have sprayed with Rose clear but no good? 1 Answers 0 Vote Up Vote Down Gerry Daly Staff answered 4 years ago Roses do not grow well in a tub and are prone to disease, spraying cannot counteract this fully. Best to plant them out in the open soil or make a hole in paving to give them free root run.