its not magic....here is the basics for ya....
Topping, Pruning and Bending Cannabis Marijuana Plants
Topping, pruning, and bending are all methods marijuana growers use to alter the growth pattern of cannabis......
Pruning Marijuana- Pruning is the removal of unwanted, often dead foliage. Pruning away old yellowing leaves helps to preserve the health of the garden. Never remove healthy leaves. Pruning marijuana is also done to concentrate growth into certain favored areas of the plant. Pruning is done in some cases to prevent the spread of disease. Any removal of foliage or branches will slow growth for a few days while the plant recovers. Try to snip or cut when pruning. Over-pruning leads to plant shock leading to all kinds of problems such as stunted growth and/or death.
Topping Marijuana- Topping a plant refers to cutting off the top shoot(s) of cannabis plants. You can pinch, clip or snip off the tallest shoots or the freshest shoots. Cut the branch stem just below the last fully developed node,. The plant starts developing branches at the remaining nodes. This is a good techniques to keep a plant short and bushy. Or you can develop many top colas instead of just one. Don't top a plant more than twice and never top when it is in the flowering stage.Bending Marijuana - Carefully pull down the branches of your cannabis plant, or the whole plant, tye them down. You are now forcing them to grow horizontally. Tthe nodes will start producing branches or buds that grow straight up. Bending should be done gradually to avoid pinching or snapping the stem. Use soft hemp string or cloth to secure the branch or stem loosely when tying down to minimize damage to the soft stems. Growth is slowed for awhile as the cannabis plant adjusts to the shock of being bent. This is a good technique to maximize space in a small grow room.