The process of topping is just about as simple as the name implies; cutting off the top of your plant. Sounds crazy right?
It makes sense when you think about though. Certain plants have a growth pattern that makes them grow taller, with a focus on a central flower. While other smaller flowers may develop underneath the main flower, they won't be as vigorous or strong due to the energy focusing on the top of the plant.
While this isn't the case with all varieties of flowering plants, when you're growing a plant with tall vegetative growth and a centralized growth pattern, you can benefit from topping.
Topping your plants might sound as simple as chopping off the top portion of your plant, it is a little more in depth than that.
During the vegetative stage of your plants' growth cycle, cutting off a specific portion of the top of your plant can focus more growth hormones to the lower half to a more lush and even canopy. After being cut, your plant will use more energy to regrow its central flower, and a portion of that is distributed throughout the rest of the plant.
For the first topping, a good rule of thumb is to cut the plant above the 5th node of your plant. Doing so will give you enough branches on the bottom for your plants to bush out properly.
If you want to continue toppings on the same plant, be sure to cut each branch above the second or third node to allow the plant to grow out properly. These toppings are more subjective, and will depend on how much you want the plant to bush out and how big you want the final plant to be.
When you top the plants, you are completely removing the upper growth. No new growth will develop from the growth tip that has been cut. This allows the lower lateral growth to assume the dominance. Since there are two growth tips at each node, you effectively double the number of dominant growth tips every time that you top the plant.
Topping doesn't work with all plant varieties. It is most ideal for plants that have strong upward growth, with multiple nodes for branches and flowers to develop. This way when you cut off the top of the plant, the bottom portion is nearly identical.
The goal of topping is to add increase growth outward instead of upward, so if your plants are naturally shorter and grow wider instead of taller, topping isn't something you need to worry about.