Question
Four years ago, I purchased three Rose of Sharon trees in pots.  I planted them in the ground.  Two have done well, but one needs to be staked from two sides all the time because its root ball seems not substantial enough to hold it upright.  It still blooms and the leaves look good, but the trunk is not growing like the others.  Can I do anything to increase the roots.

Answer
Lynn,
I would suggest that you change the type of fertilizer that you are using. Nitrogen fertilizers stimulate top growth while low nitrogen fertilizers stimulate root development and structural strength. Use a 5-10-10 or equivalent fertilizer to help this plant along.
Good luck.
Ed Gulliksen