How To Mainline Cannabis Plants

A Cannabis Mainline

Mainline training is the best way to break apical dominance and produce cannabis plants with several colas rather than one. I explain the key benefits of mainline training in our article, “Mainlines & Manifolds: the best ways to train cannabis plants”. There, I compare mainlines to other training practices and explain the science behind our claim that it is the best way to train cannabis plants. I invite you to read that article first to be sure that mainline training is right for your cannabis grow. In this tutorial, I cover how to mainline cannabis plants. I answer the common questions about mainlining cannabis and provide a step-by-step tutorial for mainlining cannabis plants.

This article is part of our comprehensive guide to mainline and manifold training for cannabis plants.

The Coco for Cannabis Guide to Mainlines and Manifolds

Cannabis Mainline Training Q&A

What is a Cannabis Mainline?

A cannabis mainline is a plant that has been topped three times at symmetrical nodes to produce eight equal main branches or “colas”.

How is mainline training different than manifold training?

Both mainline training and manifold training are techniques to produce plants with eight main branches or colas. Mainline training involves topping the plant three times at symmetrical nodes to produce eight equal main branches or “colas”. Manifold training produces eight main branches with only two toppings by preserving four branches on each side of the plant during the second topping. To learn more and determine which is the best cannabis training method for your plants, see our article “Mainlines and Manifolds: The Best Ways to Train Cannabis Plants”.

Is mainline training good for beginner growers?

Yes! As long as the plants are growing well, any grower can execute a mainline. It is a systematic approach that takes out much of the guess work. Just follow our step-by-step guide to mainlining cannabis plants below.

How long does it take to grow a cannabis mainline?

This depends a lot on your media and style of growing. If you follow our style of high frequency fertigation in coco/perlite, then you can complete mainline training and be ready to flip the plants to flowering in as little as one month from seed. See our article “Growing Cannabis in Coco with High Frequency Fertigation” to learn the keys to growing in coco. In deep water culture growth rates will be similar. However, in soil, it could take 6-8 weeks before plants are ready to be flipped.

Is mainline training good for seeds and clones?

You can mainline plants grown from seed and from clone. However, only seedlings take full advantage of the technique. Because clones lack symmetrical node growth, they are easier to manifold than to mainline. I recommend mainline training for seedlings and manifold training for clones. I have a special section on manifolding clones in our tutorial, “How to Manifold Cannabis Plants”.

Can you mainline auto-flowers?

It is technically possible to mainline auto-flowers; however, it is difficult to accomplish in the time available. Topping should not be done after the plant has entered the flowering stage. This means that with most auto-flowers you will only have about 30 days to complete the three toppings required for a mainline.

Mainline training an auto-flower is ambitious for most growers. However, if your plants are growing well then it will be possible to do manifold training. It is obviously important to get the plants growing very quickly to accomplish this. I offer advice about how to manifold auto-flowering cannabis plants in our guide, “How to Manifold Cannabis Plants”.

How many cannabis mainlines will fit in my space?

Cannabis Mainlines become large plants. They can occupy a huge footprint if trained out wide. Alternatively, they can be kept in a pretty small space if you allow them to grow vertically. I think the ideal is to have about 3-4 square feet per plant.

In a 4x4 tent, I have grown as few as 2 and as many as 6 cannabis mainlines. Six was too many and two of the plants suffered from inadequate space. Two plants easily filled the space, but the yield on that grow was about 20% lower than my average. I think 4 plants is the sweet spot for my grow.

Cannabis Mainlines will grow a lot, so be sure that you have adequate space. If you try to cram a lot of plants into a small footprint, you had better have plenty of vertical height to allow them to grow up. If your vertical height is limited, then you should grow fewer mainlines and work to spread them out horizontally.

Equipment & Supplies for Mainlining Cannabis

If you plan to do any topping or pruning then you will need to get a pair of pruning snips. These will also be your number one tool for trimming the harvest!

Fiskars Non-Stick Softgrip Microtip Pruning Snips
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These Fiskars snips are really the best on the market and every grower owes themselves a pair. We linked the non-stick version because that feature really helps later when you are trimming the sticky resinous colas.

Slim Soft Ties
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Plant ties are used to secure the plant during training. They hold the plant in place but do not injure the plant. You can use other household items like string or yarn, but they are not nearly as convenient as proper plant ties. What ever route you take, avoid using anything that is too narrow or sharp. Things like fishing line can actually injure the plant.

Soft ties are my preferred plant tie solution! I bought a couple spools several grows ago and continue to reuse the pieces on every grow. It is a soft coated wire that is easy to bend and shape, but rigid enough to support and restrain cannabis plants.

When you are training or working around your plants you may accidentally injure them. Stem splits and tears often occur during low stress training (LST) or supercropping. Many growers use a sticky tape such as electrical tape to wrap around these injuries. While it is important to wrap up the injury, you should never put sticky tape on a plant, because it will lead to further injury!

Grafting Tape
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Grafting Tape is the professional horticultural solution for this problem. Grafting Tape is more like kitchen plastic wrap, in that it sticks to itself and creates an air tight seal, but it does not stick to the plant. It also expands to accommodate plant growth. Every grower should buy a roll! It is the correct product to help heal injured plants and it is quite inexpensive.

Dr. Coco’s Cannabis Mainline Training Tutorial

In this tutorial I use the terms “node”, “growth tip”, “top” and “cola”. For clarification of these terms, please see “Cannabis Training Terminology” in our guide, “Mainlines & Manifolds: The best ways to train cannabis plants”.

Step 1: Grow the plant to six nodes

The first step in mainline training is to grow the plant out to six nodes. It is important to wait to allow the plant to develop six nodes before topping for the first time. As we explain in our article, “Topping Cannabis Plants: Why, When & How”, if you top earlier than this you risk stunting the plant. It often seems counterproductive to new growers to wait for growth and then cut it all off. However, the growth that is most important during this time is in the root system. Leaving the plant unmolested until it develops six nodes ensures that it has adequate time to develop a good root system. An established root system will prevent shock and help the plant to recover quicker from the topping.

Trim the Tips, but Leave the Leaves

During the early growth of the plant it is critically important to keep every single leaf that you can. The leaves are powering the growth of the plant and removing them will slow the plant’s growth considerably. That said, you can and should remove the growth tips that you will not keep. In both mainline and manifold training, we only keep the branches from the third node on the main stalk. That means that we need to trim off the branches from the first and second nodes. You can trim these as soon as you can safely cut them away without injuring the adjacent fan leaf. Remember, trim the tips but leave the leaves!

In early life our job as growers is to encourage healthy growth and good root development. As with all plants, I recommend starting in small containers and potting up. Be sure to read our article, “Transplanting Cannabis Plants: Why, When & How”.

Plants are often ready for final containers around the same time that they are ready to be topped for the first time. When I use half-gallon second containers, I often transplant to final containers before topping. In larger second containers, you should plan to do the first topping in the second container and then transplant to final containers. Both topping and transplanting can be stressful events for plants. Therefore, you should always separate them by a day or two and verify the plant has recovered from one before doing the other.

Step 2: Top the plant to the third node

This is a pretty simple step, but it can be hard to bring yourself to do it. We spend three weeks or more nurturing these little plants and then we are supposed to chop them in half. If you struggle with this step, then you are like virtually every other cannabis grower who has tried it. However, I assure you – it will work out for the best in the end.

We top mainlines to the third node. This means that we remove the fourth node and everything above it. The branches growing from the third node become the two new “tops”. They are the main branches, and each will be topped again in time. The lower branches from the first and second node were removed during step one. Therefore, following this first topping there are exactly two branches on the plant.

Leave a stump

When we top the main stalk to make a mainline, it is important to leave a stump. Avoid cutting close to the third node. Instead make the cut just below the fourth node. This leaves a large section of “stump”. It may look ugly but helps to prevent stem splitting. As the plant grows, it will eventually envelope this “stump”.

Use sharp snips like the Fiskars snips that I use. Apologize to the plant if you feel that you are betraying her, and then it is just a quick snip and it’s done. If you have space, you can take the tops that are removed during this topping and clone them.

Step 3: Grow both branches to the fourth node

Following the first topping I allow my plants to grow unimpeded until each main branch is working on its fourth node. In coco, this usually takes 5-6 days. It will take somewhat longer in soil.

There are manifold training guides that recommend aggressive training during this stage. I disagree with this approach and argue that it is counterproductive to our ultimate goals. You can gently bend the branches away from each other if they need space, but aggressive bending and supercropping should wait until these branches have reached past their third node.

Again, Trim the Tips, but Leave the Leaves

Some guides recommend defoliating the plant as it grows and removing certain fan leaves. This is always a mistake. Leaves help power the growth of the plant. With mainlines it is particularly important to not defoliate early. We are repeatedly topping the plant which costs the plants enough leaves as it is. The plant needs to keep every single leaf that it can to power growth during the process of mainline training.

While we always want to leave the leaves, it is again a good idea to trim the growth tips that you will not keep. As the two branches grow they will produce growth tips at their first and second nodes. These growth tips can be removed as soon as it is safe to do so, just as we did on the main stalk in step one.

Step 4: Top both branches to their third node

When each main branch has grown past the third node it is time to top them again. Unlike, the first topping, it is not important to let the plant grow much past the third node. Initially that is important to allow the plant to establish a root system. At this point we can top the plants as soon as they are ready.

You can do the second topping as soon as you can safely cut the main stalk without injuring the tips on the third node. It is helpful to wait for the fourth node to start to push away from the third to have room to make the cut. However, you can also gently pull the leaves back to expose and cut the stem earlier. Just make certain that you do not injure or remove the two growth tips on the third node.

Following this step, you should have four growth tips remaining on the plant. There are two main branches and at the end of each there two 2 growth tips. They will be small when you first do the topping, but they will grow very quickly once they are the sole focus of the plant. You can expect to be ready to top them in only a matter of days.

Step 5: Train the main branches

After the second topping it is time to begin really training the two main branches. Our goal with training at this point, is to spread the branches out and keep them even. During the process, it is important to keep the two sides at the same height. If the tips on one side are higher than the tips on the other, the high side will gain dominance. Keeping the two sides even as you train ensures that the future growth will be distributed evenly.

The reason that we spread the plant out is to make the most advantage of the light. Directing the growth outward means that more of the plant has access to better quality light. It also allows each branch to have adequate space to develop.

There are two options for this training. You can use low stress training (pictured), which is gently bending the main branches down and securing them with soft ties. Alternatively, you can "supercrop" the two main branches. Super-cropping is a technique based on pinching the stem to break the inner core. Softening the stem in this fashion allow us to bend and fold branches without injuring them. I discuss the practice of supercropping these branches in our tutorial, “When & How to Supercrop Cannabis Plants”.

Step 6: Top the four branches to their first node

The third and final topping will be only a few days after the second. The four small growth tips that remain after the second topping will grow quickly. Furthermore, we can execute this final topping at the first node rather than waiting for the third.

As soon as the plant is pushing out the second nodes on all four branches you can top them. Again, be careful not to damage the tiny growth tips at the first node that will become the main colas. If you are concerned about doing this topping accurately, just wait until it is easy to cut the stem between the first and second nodes.

When you complete this third topping on all four branches you have completed the core process of mainline training. Your little plant will still be small, and the eight growth tips will be tiny, but the foundation is in place. With proper care, mainlines will grow quickly once they are complete.

The Next Steps

Once you have eight main branches, the mainline structure is complete. The plants are usually about four to six weeks old and entering the late vegetation stage. This is an exciting time for cannabis mainlines because the growth will explode over the next several weeks.

See our guide, “Training Mainlines and Manifolds in Late Vegetation and Flowering” (Coming Soon), for tips on how to manage the rest of your cannabis mainline grow.

Start a Grow Journal!

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The Coco for Cannabis Guide to Mainlines and Manifolds

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Author: Dr Coco

I am a university professor and have taught courses in horticulture. I am coco for cannabis and I hope you are coco for cannabis too :) Grower Love!