Ok, I'll take this one... This method is called "topping" and may or may not be a good idea, depending on the strain. I have noticed that some varieties will react really well, and give you 4 main colas, each as big as the regular one would have been. With some strains, however, I have seen the 4 'topped' tops be less yeild than an untopped plant of the same variety in that crop. My advice: Always test! Just top some of the plants (about half), that way you can compare the topped plants to the untopped plants. This being said, some Bushy varieties have enough side Colas to more than make up for the need to use this method.
To "Top" a plant, you must cut the new growth coming out the top while the growth is still very young. It depends on how long you plan on vegging when you would want to top. If you want to veg short, the top should be sliced off with a sterilized scalpel or razor blade at probably your 4th or 5th internode. Personally I wait till the plants are about a foot tall, then top some of them to create plants with 2 tops. This can be performed a second time to each new top, usually on the 2nd or 3rd new node after the origional Cut. Always use a sterilized scalpel or razor blade. You don't want to give them any infections, or let any fungus take hold! You can continue to create more tops if you want, but at this point you may be sacrificing yeild. Make sure you have some with some topping, and a couple with more topping, and some with no topping. then the next time through, you can do the one that yeilds the most!
It's important so I'm emphasizing: When you first try this, don't do it to all the plants, just do it to a certain percentage, hopefully 50% or less. This will mean that if you happen to be growing a variety that des not respond well to topping, you will not be destroying you whole crop. The advice from the person above is good, accurate advice as well. Hope that helps!
