The physiological reason why plants get bushier when the top is cut off or bent is that one of the hormones that will be no longer made by cutting the top of the plant used to prevent the branches from growing, this is termed apical dominance. Without the plant top, the branches will be grow at an increased rate from their meristem tissue, termed secondary meristems. This means each branch will elongate, and each branch will secrete more hormones. In some plants, one of the branches will become ‘dominant’ and suppress growth of the rest of the plants, making the plant start to grow tall again. Other plants will just become bushy and will have lessgrowth in height.Good growing,
Dr. E.R. Myers
* I more often recommend bending the top of the plant, this will slow the hormones, and make the plant more bushy (less tall) without the stress of recovering from cutting off the top. The benefit is that bending does not result in several days where the plants do not grow because the apical meristem was lost and the growth hormones, are gone.