Topping, a popular cannabis plant training technique, involves the strategic removal of the main stem's top. This method presents a cost-effective way to generate additional colas while maximizing light exposure. By employing topping, cultivators can achieve larger marijuana yields and optimize their growing space efficiently.
Most plants naturally possess a single main stem. Topping involves the deliberate removal of the apex of this main stem to encourage the formation of two separate stems. These newly formed stems have the potential to develop into individual buds or colas during the flowering stage. Through a single or multiple topping sessions, growers can significantly increase the number of bud sites under the grow light while ensuring a wider and more compact plant structure.
If left to grow naturally, a marijuana plant typically develops a solitary main stem, resulting in a single large cola. However, by applying topping during the early stages of growth, cultivators can stimulate the plant to produce multiple colas within the same timeframe. This approach enables growers to cultivate more buds in limited space while utilizing the same grow light efficiently.
When to top
Your plant should have 4-5 nodes grown in. This is typically around the fifth to sixth week of your harvest. Anything past six nodes will be too late to top.
What are nodes?
Nodes are the two stems that are connected to the main internode. As the nodes grow in, they will alternate in a 90 degree angle. When topping, count the nodes going up the main steam. After you have passed your fifth node, you will know where to top. 
Photo Credit-Amsterdamn Genetics.
What to use
You will want to use sterilized scissors, and cut at a 45 degree angle. It is extremely important that they are wiped down with rubbing alcohol, followed by drying with a paper towel, before cutting. We do not want your plant to get infected!
End Result
After topping your plant, you will see your plant start to grow wider. The nodes will become stronger and healthier, resulting in a bigger yield.