Greetings!

I would like to do some research on fertilizing plants, when it is appropriate to do so, and why. I am interested in knowing about 'when' a plant uses different nutrients. For example, I know a plant doesn't use nitrogen during the colder months, but what signals the change... is is hormones? day length? temperature? And if plants can't use any of the Big 3 N-P-K during the winter, what about elements such as iron or magnesium?

Take a saw palmetto, for instance. Last winter I noticed (maybe for the first time) how yellow they had turned out in their native habitat, uncultivated. Then through the summer they were nice and dark green and healthy looking. And this winter... yellow again.

Can anyone give me any clues or refer me to any links on this subject?

Thanks so much,

Kay