When is best time to prune a Globe Willow Tree
I want to walk under trees. these start about waist high. we live in NM
The best time is in the spring when they leaf out to see what branches need to be thinned out or cut. You should not cut these trees too far back and depending upon how old they are, you may need to prune/cut back over a couple seasons. You should not cut more than a third.
I would do this in late winter or early spring just before it leafs out. If you do your pruning then, the tree will not waste its energy on branches you are going to remove. As Renee says, avoid over pruning, as doing so can make a globe willow susceptible to frothy flux, which can bring about the tree's demise.
I think spring is best, but all through spring and summer, I pick off the little new branches that pop out.