I have a 15 year old lemon tree in a pot that I take in over winter (I live in Connecticut). It is 4-5 ft. tall and it has 7 or 8 small green lemons on it now. I want to know how to correctly fertilize it. I have used Miracle-Gro (8-7-6) all summer, but the leaves seem to be paler than they should be. Otherwise, it appears to be very healthy, with the occasional yellow leaf that drops off. Is there something else I should use to fertilize?