My roots after three weeks. Pic...

Pulled this baby out of her two gallon plastic pot to transplant into a three gallon smarty.

I've read that two gallons should be enough room for two months of growth give or take but seeing this makes me skeptical.

This is the second jump up in put size she's had.

The 1 month per gallon rule of thumb is based upon the amount of soil nutrients that can be depleted in a given amount of time. Not how far the roots can stretch during that time.