I live near the ocean in Southern California. I have potted roses on my front patio. They are frequently getting a white mildew on the leaves and buds. Does anyone recommend a remedy (non-toxic preferred)?
Powdery mildew can run rampant in a damp climate. Make sure the roses get plenty of water. A well hydrated leaf has better resistance to mildew. Water the soil, not the leaves, because dampness on the leaves will encourage mildew growth. You can make an exception if there is already mildew present... in that case, watering the leaves can help rinse away the spores. Just make sure to do it early in the day so the water has a chance to evaporate. Since your roses are in pots, you have the luxury of moving them to a sunnier location if neccessary so they can dry.
You can make a non-toxic spray by mixing a spoonfull of baking soda in a quart of water. The alkalinity will inhibit the mildew growth, but you're not going to get rid of growth that is already established. Prune away areas that are really ugly.
Finally, make sure there is adequate air circulation. Prune so that the interior of the bush is not crowded with branches.
Did it aswell
I did the exact same thing last summer, PM me and i will be able to help you out.