Nature Hills sells several different single stem tree form Hydrangea paniculata types. They are all hardy and easy to grow, but each spring it is best if you spend ten minutes pruning them before they start to grow.
It is best to remove about 1/3 of the length of each of the stems leaving a somewhat irregular “ball on a stick.” Pruning should be done before the new growth starts each spring.
The photo shows a young plant that is only a couple of years in the ground and how it should look once you are done pruning it.