Question
We planted three columnar aspens last year.  This year each tree has one or two leaders that have grown about 4 feet with leaves that are about four times larger than the rest of the tree.  The rest of the tree has stayed the same height with small leaves.  Should we prune the new growth back so the older parts of the tree can catch up?

Answer
A leader to me is the top branches and these should not be pruned since this is where the height growth comes from. The larger leaves are just new leaves and is normal. Newly planted trees are somewhat like teenagers they grow fast and these growth spurts make them look out of proportion. This is all normal the tree will catch up. Side branches can be pruned but I would wait until next fall after leaf drop to do any pruning. This is a young tree and needs all the foliage to generate food for a good root system.