It seems very illogical to think that your crape myrtle needs fertilizing when it's doing fine and has been doing fine without fertilizer for many years. Why would you want to do this??? Improper fertilization is a major source of failure and a variety of problems with woody plants. People want to "love" their plants to death, and sometimes do.

Fertilization should only be used to correct an established nutrient deficiency in your soil. If your crape myrtle is doing just fine, there probably is no deficiency. If you have some reason to believe there is a deficiency, have a soil test conducted to determine what nutrients need to be added.

Boothbay,
Brandon is so eloquent.
If it aien't broken, don't fix it.

this shrub.. which has grown into tree size .... has thrived in your world with little or no assistance from you ... congrats ...

so why now.. are you trying to turn it into a child who needs to be fed ...

IGNORE IT ... as you have been doing.. thats how you deal with trees and shrubs ...

and BTW.. at 20 years.. it is no longer a child .... it is grandpa ... lol .. only reinforcing the facts that it needs no TLC ...

just give it some extra water if a drought comes along...

dont try to kill it with too much love ...

ken

Crapes can be terms trees OR shrubs, depending upon the size and form.

The best thing you can do for your tree is to add a generous layer of mulch over a large portion of where you 'guess' the roots are. The roots can extend far beyond the reach of the canopy, so think big.

Since you don't water this plant, I'd absolutely not fertilize it. I expect that you will see some nice results just from the benefits your tree will receive from the mulch.