Ive found other than the right strain, you need strong light, and great air flow. I train the plants so they grow horizontally, and grow into a hedge. I usually don't grow them straight up. I also shake them, and mess with each individual branch, and growing tip up to a point, and then I just leave them alone. I do not top them ever. Ive found that sets them back 2 weeks. It may be ok if you give them the extra time for the 2 new shoots to grow as large as the original growing tip, and then make up for the lost veg time. That works, but reduces harvests per year.
I also have fans going 24 hours a day. Even when lights out. Temps range from 75-84 at the canopy.and good fresh air flow. That's it.
Actually to get really technical.
I use 3.8 cu/ft bales of Promix BX. Which in reality is 28.4259 gallons of Medium.
I get 2 x 20 gallon totes and a couple 5 gallon buckets left over, which also in reality, is no where near 5 gallons of soil.
But in the 20 gallon containers Its actually closer to 10-11 gallons of actual Medium.
I just use 20 gallons loosely, as I use a 20 gallon tote, and fill it to the max, which really incorrectly inflates the amount of actual Medium.
So I'm getting closer to 2oz per actual gallon of Medium.