Feed what and when ?

Most any commercial fertilizer works fine. They do NOT require a lot of fertilizer so don't overdo it. I normally mix in a pint of dry fertilizer (8-8-8 or 10-10-10) about three times a year into a 5 gal. bucket of water. Let dissolve and pour around the base about three feet from the trunk. Its worked well for my river birch which were 3' tall when I planted five years ago. They are now 40' and doing well!