Below 20% Humidity

Can someone please explain the side effects of extremely low humidity in ones grow room?

If I understand it right, plants not only draw moisture through the roots but they get some of it that is absobed through the leaves which are needed for photosynthesis. If the humidity is too low they have to rely on the roots for everything. This will draw much neeed water and nutrients away from the production of buds.

Will it affect the plants as much if they are only vegging?

It affects them more while vegging. Humidity needs to be at about 60% for vegging and drop to about 40% during flowering. Too low during vegging and the plant wont bulk up and get ready to make buds. Too high during flower invites mold. Get a humidifier if you can spare the bucks. Or if you are broke as I am, just set a couple of pans full of water in with the plants.

thanks for the info man