|Just before the weather turned cold here ourside of Washington DC, my four-year-old potted miniature roses began to develop soft-grey splotches that I assume is mildew (and I just kicked the spider mites this spring!). I understand that my best chance atfighting mildew is an upside-down -bucket-bath of baking soda, a drop of dish liquid & a drop of veggie oil in water, and that I shouldn't get my hopes too high. However, would it be better to let all go dormant in the early-winter air (25-50 degreesat this time of year) than to begin a bathing & fussing regime? My suspicion is that the plant may be okay with a proper winter's nap, and consciencious preventative treatment in the spring.
|I agree - the fungal disease took advantage of moderate temperatures and humidity in fall to strike, but if the plant isn't suffering too much, just remove the affected leaves and allow the rose to go dormant. Miniature roses are surprisingly cold-hardy, so unless your variety is particularly sensitive, you can allow it to stay outside and go dormant for the winter. Sink the pot in an area with well-drained soil, water it well, and heap leaves over the base when frost really sets in. Prune back dead,twiggy or crowded growth in early spring before growth begins. Powdery mildew's favorite time to get established is when days are warm, nights cool and humidity is high. Mist the leaves with this recipie to ward it off: 3 teaspoons baking soda and 2 tablespoons of summer horticultural oil to one gallon of water. I'm not sure how interchangable vegetable oil and hort. oil, are, but you're welcome to experiment. Treat just a few leaves at first to make sure the plant can tolerate it.
If you want to keep your rose indoors for the winter, stop feeding it, but continue to water just enough to keep it from drying out completely. Move it to a spot where it gets less sunlight. When you see growth begin again, move it back to its "summer home", and resume feeding.