Pruning is always done by tomato farmers to increase the yield. The small shoots between the branches and the trunk are removed so all the energy is used to maximize fruit production. But also for marijuana plants it's very effective to remove these useless shoots so the plant can develop bigger buds. Using this technique you will get a few big, hard and heavy buds instead of many smaller ones.
Pruning is mostly done by professional cannabis growers who wants to yield the maximum amount of weed per square meter. Because there is no energy wasted on the small buds and small leaves the top ones will grow bigger and heavier. The top buds will also get more light because they're all at the same height. Download my free marijuana grow bible for more tips about growing marijuana plants.
Pruning should only be done during the vegetation stage because the plant needs time to recover and grow big leaves. Wait at least 3 days after pruning before forcing them into flower. Make sure your marijuana plants are growing again and drink enough water. Go easy on the fertilizers and give them a few days to recover. If you have mastered this technique and do it at the right time it will definitely pay off. No more small and fluffy buds. You will only get big, hard, and heavy marijuana buds.
If you use the SCROG (Screen of Green) method you also have to prune your marijuana plants. Place a screen at 50 cm above your plants. Take the top out of every plant when it's 10 centimeters from the screen and wait until the new tops grow through the screen. Wait until they grow 10 centimeters through the screen, gently bend them and connect them to the screen. Prune your marijuana plants after the first shoots have grown through the screen. Wait a few days and force them into flowering. During the first two weeks of the flowering phase your marijuana plants will keep growing.
Combine the pruning and the SCROG technique and you can grow 1 gram of marijuana per watt of light. So if you have 1 600watt HPS bulb you should be able to grow 600 grams of cannabis. Temperature, humidity and other factors also have to be right of course.