Ditto to the 6' high and wide w/ extensive root system on the Texas Gulf Coast.
Many of us don't think about root pruning, but Knock Out might successfully be container-grown, even in the south, if the roots were put in balance when the top was pruned..wear long heavy gloves
. I know people who also do that with Citrus down here...Bonsai on a bigger scale.
In fact one could root prune an in ground plant. Just take a sharpshooter (what are they called up north?) and dig straght down around the whole plant a few feet out. Makes the root system more compact and keeps the plant top from growing as fast.
