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Several years ago we planted a row of 4 of these trees about 5 feet apart in a raised planter here in the high desert of northern Nevada. All of the trees are healthy and looked nearly the same when planted, but one on the end has fallen far behind the others and it's branches are only about 2 feet long, while branches on the the other three are trailing 6 feet onto the ground. All are on a drip system that has been checked for flow (the tree of concern has been getting a bit of extra water by hose) and sun exposure is the same for all. What would we have to do to help the third catch up? Is it possible to graft branches from the others or is there some fundamental shortcoming of the 4th tree that is causing it to put out only short branches? Thanks in advance for your advice.