How do I get my lilac trees to grown faster?

I planted 7 Lilac trees about 3 years ago. The one side with 3 trees are thriving. The other side with 4 trees is not doing much at all. Two trees have had to be cut down to the ground and the other two are hanging on, but not looking great. The neighbors have bind weed along the fence line and that is what got a hold of those two trees. Second question if the bind weed root is underground, how can I get rid of it and help the trees I plant there? Two weeks ago I planted 3 Arborvitaes along that fence line and I am hoping they thrive. Help.

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