Fertilizing trees is a great way to keep trees healthy and is especially important for revitalizing sick trees. I highly recommend you read my four part series on tree fertilizers. You can access them by clicking on the fertilize link under categories on the right sidebar. This article is aimed at pointing you toward a few fertilizer products you can buy to do the job yourself. Some of the tips here will help you with the timing of the right application, but you do need to read the label of the product you are using to make sure you are applying it at the right rate.