My ginkgo (which was grown from seed) was transplanted twice before it was 3 years old, when it "died" from lack of water by my ex-wife. I dug it up and transplanted it again, and a new sprout came up. After 2 years I moved, transplanting it again. It did well, but has had winter-kill for 3 years. The main stem is dead in spring, and a new shoot comes up to about 1 meter. This winter was particularly mild, with only a week of really cold temperature. Any ideas to keep this from happening again?