We have two dogwood trees in our yard. One is 6 years and one is 5 years. The leaves of the younger one have turned a crisp gray brown. This has happened over the last several weeks. We read that if there is a unusual warm dry time that a dogwood needs extra water at the edge of the roots. What kind of fertilizer should we be using? The edges of the older tree are beginning to look the same way. Should they be ferterlized now or wait until spring?