The reason for topping your plant is simple: It makes your plants look bushier and grow the most Colas (Top Buds). This is sometimes known as Super-Cropping.
Other than super cropping, topping helps if you have a height limit (ie: growing in a tent) and also is you like cloning, the top can sometimes be the best clone.
Here’s an example:
Non Topped 
Topped
*Rule of thumb, have at least 3-4 nodes before you top the first time.*
Topping involves removing the top of the plant which allows the side branches to take over.
Different spots to Top:
1-Top cut, Most common, Suggested.**Taking of the Top node.**
2.Lower Cut for more intense training purposes
3.Max training and height requirement. Do not cut here. This is where you take nice clones.
The top buds are always the biggest and heaviest of the branches, therefore it would be better to have 8 main colas than 1 cola and a bunch of side branches.
One main cola, smaller side colas. 
Many same size Colas
Pic on left: Indoor plant, grows smaller, veg ~5 weeks before flower.
Taking the pictures above, forgetting the size because outdoor plants grow larger, you can see from the picture on the left how when you don’t top the plant you get one main center Cola and then side branches about half the size. Topping the plant gets you the even canopy.
This will basically allow you to maximize your return. Mixing topping and trimming properly will get you the most out of your plant.
Before Topping 
Before Topping 
After Topping and slight training. 
Before Topping 
After Topping 
Both Topped Plants
Certain plants can grow slightly different, but topping besically remains the same. You are removing the top new growth of the plant, to allow the lower branches to catch up and become a top branch.
Day of cutting and 3 days after 
Day of cutting and 3 days after. 
Top view 3 days after 
Top view 3 days after
By cutting the top, the two side branches directly below it will split the extra energy and both will become the new top branches. After a little bit more time, top again, to produce 4 new top branches. This can be done at the same time as you trim and train your plants to shape them the way you want.
Why You Should Not
Here are a few reasons not to Top your plant. The First and most important is: **IF you have AUTO-FLOWERING SEEDS**
This is because when you top a plant, it takes a couple of days to recuperate. With auto-flowering seeds, you only have a certain amount of time before the plants flower so you may end up having a much smaller plant than you expected when it starts flowering. 5 Days is a big difference when you only have 30 days to veg. This could also apply for photo-flowering plants if you were trying to spend the least amount of time in veg and flower your plants quickly.
Topped 
Not Topped
The other reason, would be based planting density . If you have a lot of plants in a small space, the plants will fight for light, so removing side branches and focusing growth on the main stem would allow for better light distribution to all plants. This would be more of a SoG (Sea of Green) method.
If you have any additional questions please leave a comment or email us.
Happy Planting,
Canadian Grow Guides.
