Topping is a method used for a few reasons. First, it causes your plant to grow shorter and bushier, rather than tall. It also significantly increases the yield you get from your medical marijuana garden. Most gardeners prefer to top their plant after 5 sets of nodes have formed on the plant, but it can be successfully done as early as when the plant has 3 sets of nodes.
While we already stated the benefits of topping, there are a few downfalls as well. First of all, topping has shown to slow growth, although not significantly. Also, while you will have more colas, the buds on these colas will be slightly smaller. Most gardeners also prefer not to top more than 3 times, as this tends to be very hard on the plant.
To top your plant, cut the main stem, just below the newest leaf formation. Usually after a few days, the small leaves which were coming in under where you topped will have grown to become the new top of the plant. You can repeat this process up to 2 times.
If possible, be sure to use sterile scissors whenever you cut your plant in order to reduce the risk of infection. You should also note that topping should only be performed during the vegetative stage and should NEVER be done during flowering. This is because when you switch to the 12/12 light cycle, the plant starts focusing its energy on flower growth rather than leaf growth. If you top it in the flowering stage, you will have basically cut off one of your colas.