FAQ

Spring and early summer are the times of year most commonly recommended
for fertilizing. Most of the time, most trees only need nitrogen. A soil
analysis will tell you if phosphorous or potassium should be added. The
general rule of thumb is to apply one-eighth to one-quarter pound actual
nitrogen per year for every inch of trunk diameter. So, a tree with a trunk
about 2 inches wide (diameter at breast height)should get about 10 ounces
(five-eighths pound)of ammonium sulfate every year. You could apply this in
spring only or you could split the amount into two applications - one in
early spring just as buds break and again in early summer.
 

The best time to prune is in spring before the tree leaves dormancy but
after the coldest part of winter is past. However, it's better to prune late
than never at all, up until July. Past then, you should do only very minimal
pruning or none at all, to avoid prompting re-sprouting that will deplete
the tree's energy reserves before it goes dormant again.