For oklahoma redbuds, locusts, and mimosa are all good legume trees that can be found for free. Other
local power house trees (chop and drop) are mulberrys and hackberry. I have a catalpa too that has a lot of leaf litter to contribute in the fall. All those trees will require little or no care. On the ground I have great luck with red and white clover, plantains, dead
nettle (flower first in spring so aids in peach pollination), mints, wild lettuces, bulbs like crocus and daffodil. SE ok is higher altitude in some spots, so you may be in a microclimate of some kind.