What do I use for the CONTROL GROUP? in experiment?

I am testing what works best with growing a seed...sprite, ammonia, water, salt water. What do I use for the control group? No liquid at all?|||The accepted method to grow a seed is water, so that should probably be your control group. If that is part of your given experiement, however, then why not simply use nothing? The experiment then would be to see what works best with growing a seed as compared to no moisture at all except for the moisture in the air.