I was looking at some impatiens I had in a window box and noticed they were turning yellow. I decided to try an experiment and sprinkle some fertilizer to one side of the container, but not the other. As you can see from the picture, the fertilized side greened up and looks healthy.
From this experiment I decided to fertilize all my plants. This has been a very stressful year on the plants and there’s a good chance we may have another three months of growth.
I generally use a 10-10-10 fertilizer or something similar. The main thing I do after spreading the fertilizer is to go around with a hose and make that the fertilizer is washed off the plants and gets onto the soil.
Butterfly Gardening 