posted 14 years ago
I had the same problem, and I lasagne sheet mulched around the trees.
From top down:
dolomite / lime
water it
hay
high carbon materials
high nitrogen materials
double layer of cardboard
trampled grasses, weeds, and other organic scraps of food.
It takes time to break down, but in the long run, I found it works out the best for large areas that need help.