|What causes a white powder on the leaves of my pansies and snap dragons that are planted in pots on a north facing patio? It is also causing the leaves to slowly turn yellow and die.|
|It sounds like your plants have developed a fungal disease called powdery mildew. You can prevent the disease by providing all the cultural requirements for good growth, plus plenty of room between plants so there's good air circulation all around. The most critical is good air circulation. Snapdragons love full sunshine. They're probably stressed in your north-facing garden. Move them to full sunshine and you should see an immediate improvement. Pansies will tolerate full shade, but like a little morning sun if possible. Pinch off the affected plants parts, and rake up and remove any fallen foliage so they won't spread the disease. Here is a good home remedy: Make a baking soda solution and spray it onto the affected plants. To make this solution mix 1 tablespoon of baking soda and 2 1/2 tablespoons of ultra-fine horticultural oil with a gallon of water. The oil is slightly fungicidal and acts to help the baking soda coat the leaf and hang on longer. Apply as a spray as soon as the mildew appears and every 10-14 days thereafter. Be sure to coat all surfaces!