We have two young willow trees. I'm unsure of how to trim or look after them. They are approximately 4 years old. One is really tall, about 20 feet, and the other is quite short. I purchased both from the same place at the same time. As yet we have never cut/pruned them but the tall one is going mad when in full leaf. Any help would be appreciated.
Willows tolerate pruning, pretty much any time of year up to about 2 months before freeze up. Not much you can do will hurt it. It's a lot easier to do when they are dormant, as the structure is easier to see, and leafless branches less bulky. If you take off too much at once, the root system is now much larger than the top, and you will get a flush of new shoots.
A: Decide whether you want to keep dual trunks indefinately. If you want a single trunk, cut the other one off as low as you can. If you take off one trunk, that should be your pruning for now. Wait a month or two to continue.
B: I don't like to have branches below head height. Just makes it easier to mow underneath, but you can't do this all at once. Generally you can take off about 1/4 of the branches total at once. You decide if you want to take off low ones, or thin the middle of the tree. Me, with this one, I'd take off 1-2 feet of low branches.
If this is a tree form will, I'd probably thin it out to 2 branches in quite different directions per foot of main trunk. On branches only prune sub branches where they cross.
C: If you want a bush form willow. cut it off at the ground or a few inches up. Each stump will send out 5-30 shoots.