I moved into this new garden 3 years ago. The soil is heavy clay, and I have been improving it with compost, manure, grit etc.... and its 10 times better. However, I went to move some healthy looking shrubs today and they have practically no roots, they pulled right out of the ground with no effort. I checked for vine weevil and other bugs but could see none. There are loads of small holes in the soil from mice could it be them? Or do you think it is the clay soil? Or something else?