Tom J wrote:

...Can't you just pinch out the tops when young to cause branching and then use a
low nitrogen flowering fertilizer? I have the old fashion self seeding kind
in my yard and that works on them.

I pinch the tops out at least 2 or 3 times to get multiple stalks from each
plant before letting them go and don't use over a 4% nitrogen fertilizer about
once a month. I have solid masses of lavender & white flowers. This variety
still gets close to 24 inches, but that's over the whole growing season...




That works fine for a few plants, but when you have a greenhouse full
the hand pinching is labor intensive and adds significantly to the
production cost. That's why the chemicals were developed and are widely
used.