this is from greg green's cannabis grow bible...
FIM Technique
There is a topping method known as the FIM technique. If you push the leaves apart at the very top of the plant you should see a small bud (not flowering bud but an actually leaf bud). Use a pair of nail clippers to pinch off about 3/4 of the bud. This should result in more than two top colas being developed. In a single FIM clipping you can produce up to eight new top colas.
The origins of this technique are humorous. As the story goes, FIM was discovered accidentally when a grower messed up a topping exercise. FIM stands for: "Fuck I Missed".
Super Cropping Technique
Another method of topping is called xSuper Cropping'. By taking a branch between your forefinger and thumb you can gently crush the branch, causing it to develop multiple branches above the crushed area. You must crush it on the correct side or risk breaking the branch. Just squeeze lightly until you feel the branch give, then let go. If it gives easily then you have crushed it on the correct side. If it is hard to crush and the branch splits then you have chosen the wrong side. Practice makes perfect with Super Cropping.
Super Cropping should be carried out during the second or third week of vegetative growth and does stunt the plant. You should also note that plants that are Super Cropped can remain in the vegetative growth stage for twice as long as normal but the end result is a very bushy plant with multiple node regions that should all produce bud. Many growers have thrown Super Cropped plants away because they believed that the plants were not flowering in time. If you Super Crop your plants make sure that you have the patience to wait until the process is finished which — usually about four to six more weeks of vegetative growth.
HOW TO MAKE CANNABIS BUSHES
Some people prefer their plants small and wide. Fortunately for them, making cannabis bushes is a simple process. During the third week of vegetative growth prune half the plant's branches. Cannabis plants need at least 50 percent of their leaves in order to continue growing without experiencing fatal stunting problems. If you prune off more than 50 percent of their leaves, you may end up killing your plants.* Do not prune only one side of the plant; prune both sides to achieve the 50 percent. You may also prune the main top cola if you want to split it into two or more parts.
If the prune cuts you previously made grow new branches and leaves, you may wait until the fourth or fifth week of vegetative growth and prune again, leaving 50 percent growth.
During the seventh week of vegetative growth you'll notice that your plant has started to grow outward more than upward. Let's say you have a plant with eight shoots. That means it is four nodes high. You prune the plant and end up with 16 shoots, but the plant is still only four nodes high. Now this does not mean that you can keep doubling shoots forever. Pruning merely pushes the plant to grow all of its shoots early. If you keep pruning a plant that is four nodes high until the eighth week of vegetative growth, the greatest number of shoots you will get will be about 32. Most marijuana plants will not grow much beyond this factor, but again this is strain-dependent.
Now each new shoot has a junction point or a node that it grew from and each node should produce bud during the flowering stages. It is possible to create a marijuana plant that droops over the sides, completely concealing its own pot. With the right strain, it is also possible to have a single plant spread over an entire 6x6 foot space using this method. Creating cannabis bushes usually requires a few additional weeks of vegetative growth.
