Kathleen is following up with even more (very good) pruning questions.
"When is a good time to prune trees? I have a mountain ash and an ohio buckeye that needs some attention."
This can be done in June - it is easy to remember "prune in June" for deciduous trees. The only question I ask is why do you want to prune? Except with fruit trees, after the first few shaping and formative years of pruning, trees can often go a long stretch without any extra trimming. Ohio buckeye in particular are slow growing so I wouldn't want you pruning and slowing down their growth. Trees don't need a lot of trimming once their basic form is set. Heaven forbid you start doing massive renovation style pruning and then find you have to keep it up over time.
At this time of year I only suggest pruning to remove winterkill. Later (i.e. in June) you can remove crossing branches or anything that is suckering or growing straight up through the tree. If the tree is old keep this to a minimum. If you are in the first years of a tree's growth you may occasionally also remove a lower branch or two - but only after it is fully leafed out in June. If there is a lot of trimming to be done I always suggest hiring a certified arborist. The International Society of Arboriculture (ISA) should be able to give you a name or ask anyone you hire to make sure they are certified.