Newbie Mother Plant Question

Hey RIU!

This question may have been asked a few times, I've looked around and searched a few things but could not find the answer.

How can I keep a Mother plant at a certain size? I have about 5 feet of space(height) for my mother plant. Currently the plant is approx 2 feet high and growing large amounts daily.
I'm worried about running out of space.

Any idea on how to keep it say at 4ft? Would love to hear everyone's opinions!

Thanks!

You can keep topping it, or maybe do some lst on it.

Once The Plant Gets About 6 inches to A foot from the top sorround the side with flourescents and take away the top light.