I have 7 hackberry trees in a row. One has fully leaved out and the other 6 are coming very slowly. This seems unusual and wonder what I could change to make them all leaf out at the same time...like the used to, and be healthier. The trees are fully grown. We planted them 45 years ago. We had 10 but lost 3 of them. We lost 2 of them probably 15 years ago to an unknown cause...they defolated mid summer and never came back. (and it was not chemical damage..we are certain). They tried to sping up from the roots but the tops were dead. We lost another last year from "but rot"..it had fungus at the ground level and then a high wind storm broke it off at the ground. Thanks for any help you can provide.