first off, I suspect a 7-month old plant that is only 20" tall, has problems, ... I have gradually increased pot sizes over the years, starting with 6" clay pots, and now using #5 pots (commonly referred to as 5-gal pots) ... whatever size I used, the rootball pretty much filled the pot at harvest time ... there is a product called SUPERTHRIVE that you will see mentioned in these forums extensively ... you will see claims that it changes seeds to female status, triple sizes buds, and probably cures cancer, too ... none is true ... the one thing that it DOES do, is promote rootgrowth, which is essential to healthy plants ... next crop, start with the basics, I suspect you have poor soil pH, and probably not enough light, to have such a small plant after 7 months ... good luck :smokin: