Hi Jim,
I would not do any heavy pruning on such a young tree. You can do it in
stages from year to year. You can prune in the Spring, as other times would
encourage the
tree to put out more growth. If you want a lower more spread out tree, reduce
the height by cutting back on the main tall (leader) branch.

Sherwin Dubren

Jim Carr wrote:

I got one of those key lime trees as a gift. It's in a small planter. The
instructions say to prune it to make it bushier if I want. However, I don't
know what to prune. It's about 9 inches tall. There is one branch going off
the side. There are leaves all the way up the "Y" split.

Should I trim back the tall part? If so, how much? If not, then when do I
prune and where?

Much obliged for the feedback.