I have a variety of fruit trees. When is the best time to fertilize them?
The best time to fertilize trees is early spring, after the trees have leafed out.
In general, the least desirable time to fertilize is just before, or during, fruit growth.
Fast acting, commercial fertilizers should go down in early spring. Bulky organic fertilizers, because they release nutrients slowly, can be added later in the season (though not too close to winter) , and pose less risk of over fertilization.
In our area, do not fertilize after the end of July, because this encourages late, tender new growth that would be susceptible to winter damage.