Just like what dark side find a fert like 10-2-2 and upgrade the pot size. I found once they get root bound they start producing flowers. I think the best container size for 1 plant would be 15 gallons
When a plant becomes root bound, it produces an auxin that tells the plant to produce flowers. Essentially, it thinks that this is all the farther I can grow, time to reproduce because I may die soon.
When plants are flowering in pots, they are either root bound or have been given phosphorus as part of the fertilizer treatment.
Generally speaking, feed the plants roots and the shoots and the buds will take cae of themselves.