I'm hoping someone can help me. I have a hanging basket with lovely nasturtiums in it. It started off well, is in the shade during the morning, but gets the heat & sun in the afternoons. It is fertilized every 2 weeks & watered on a regular basis. My problem is that some of the leaves are yellowing. It still appears to be healthy, as all the new growth is green & has a profusion of flowers. Can anyone tell me why the older leaves are turning yellow & is there a way to conteract this problem? Thanks.