Subject: What should my control be for my 'plant experiment'?

My experiment is- That plants prefer to grow towards light more than gravity 
(please do not tell me as I want to find out!)
My two variables are A.a plant the normal side up with a light on its right
                     B.a plant on its side with light on the open soil side

with those sorted, I need "controls"
what should my controls be? do I need controls?

Thanks for reading.

Re: What should my control be for my 'plant experiment'?