How to

15 July 2022

Why and When to Top Cannabis Plants

Beginner and intermediate cannabis cultivators looking for a way to increase yields and promote plant health should consider topping. Topping is a plant training technique where growers will cut off the tops of the main stem of their plants after they have established. It may seem counterintuitive to remove portions of perfectly healthy plants, but topping can lead to several benefits we will explore in this article.

Topping is one technique cultivators employ to train their marijuana plants. Plant training concepts involve gently stressing healthy plants to stimulate growth and productivity. Cultivators beginning their plant training journeys may find topping mentioned alongside stress training, supercropping, fimming, defoliation, and more.

Why Top Your Plants: Plants Love Light!

The main idea behind plant training methods is to expose cannabis plants to more light. It sounds obvious, but if you consider the anatomy of cannabis plants, you will notice bud sites inside and below the canopy on the lower branches. These sites do not have the same amount of exposure to light as their counterparts in the top growth, and as a result, may not produce flowers that are as high quality or as dense.

Plant training techniques aim to expose these bud sites to more light. After the cut is made, the stems below it will grow vigorously, and after the plant has recovered, it will have at least two “main stems” where there used to be just one. Topping breaks the apical dominance – or the biological tendency of the cannabis plant to grow into a single main cola.

Apical Dominance and Auxins

Apical dominance refers to the growth habit of plants whereby the main stalk dominates its side shoots. This is necessary for the plant to keep growing upwards towards the light it needs for photosynthesis during vegetative growth. In cannabis plants, this manifests as main central colas looming large over lesser, leafy buds.

Auxins are a group of plant hormones that limit the growth of side branches and buds below the central stem. Auxins are produced in the apex of the vertical growth and are transported down the stem to inhibit lateral growth tips. When the highest growth tip is cut, the primary source of auxins is removed and stimulates lateral shoot growth below the apex.

When the apical dominance is broken, the new shoots grow uninhibited and have the chance to reach their full potential. An untopped plant will develop smaller buds below the main colas, which lack the density of high-grade flowers because of limited light exposure. The lesser buds will also be taking resources from main colas, impacting quality and yield across the board.

Stay Discreet

Indoor cultivators who need to consider their limited grow space may find topping their plants an attractive solution to keep their profile low. The “Christmas tree shape” growth habit of cannabis plants may quickly overwhelm a small grow room. By manipulating the plants to grow bushier and branchier via topping, cultivators can fill their space “out” rather than “up” and record similar or even better yields.

The Importance of Good Practice

Topped plants will grow bushier, with more substantial branching and increased bud sites. Not only will your yield improve, but it’s good practice to have backups if something happens to the main colas, such as breakage, bud rot, or mould.

Topping also ensures that genetics reach their fullest potential. By giving new growth the chance to develop as much as possible, cultivators will get a more complete picture of how their strains perform. This is useful for deciding whether or not to continue growing the same genetics in the future.

It is essential to anticipate the needs of the plants ahead of time. When topping, consider that the bushier plants will produce multiple heavy colas, which will cause the plant to become top-heavy and at risk of breakage. Growers should be prepared to stake their plants if necessary or provide a growing frame that relieves weight from the branches.

Topping plants can be beneficial for the cultivator as well. During the process, the cultivator will be observing and manipulating their plant, which helps train the eye on the plant’s growth habit, its health, and ability to bounce back vigorously from the procedure. This is an excellent practice to develop and will serve the cultivator well during the season.

When to Top Cannabis Plants – During Veg

When cannabis plants are in their vegetative stage – also known as veg – their main objective is to grow towards the light. Products of photosynthesis such as sugars and energy are put towards growing as much as possible before flowering. This stage is the optimal time to top cannabis plants as they will be established but before the flowering stage.

If the cultivator waits too long before topping their plants, they will be wasting the energy and resources the plants have put into growing up when they could have been focusing those resources on growing laterally. This may cause problems down the line, such as a weak or late flowering phase.

Counting Nodes

It can be scary to take a healthy plant happily vegging away and then cutting its main growing shoot down. To make sure you are removing the right part of the plant, it is essential to identify nodes.

Nodes are points on the stem where leaves are located. In cannabis plants, they are at the juncture of the plant stem and fan leaf petiole (the stalk attaching the leaf to the stem).

It is crucial to let plants develop several nodes before topping them to ensure the plant survives. Depending on the cultivator’s schedule, topping can be completed safely above the third node of the plant. It is common for growers to top above the sixth or seventh nodes, but any higher and the plant risks growing unevenly.

Where to Cut and Plant Recovery

Internodes refer to the stem space between nodes. When the appropriate node is identified, the internodal space above it is where you will want to make your cut. Leaving a substantial length of internodal “stump” (what is left of the main stem after cutting) high on the stem is suggested as it will help the plant recover and reduce the possibility of infection or breakage.

As topping will stress the plant (it has, after all, lost its main growing and photosynthesising shoot), it will need to recover. It is important to limit other factors that may stress it, such as underwatering or unpredictable environmental conditions.

Depending on the genetics, plants should be expected to recover within one to two weeks. The cultivator can expect vigorous growth after this as the development of lateral branching will increase the plant’s surface area that is exposed to light.

Second and Third Topping

After a period of growth, it might be time to top the plant again, and the cultivator may have the option to top side branches as well. This will create more bud sites and increase yields. Indoor cultivators with a fixed light footprint may find this as a useful technique to maximise the amount of light their plants receive. Cultivators may want to keep track of the number of days between toppings for future reference.

Disinfect Your Tools

Growers topping multiple plants should disinfect their pruning scissors in between plants. This will minimise the chances of passing viruses or diseases around. 70% isopropyl alcohol is more than sufficient.

Plant Training Synergies

Cultivators can combine the topping method with several other low-stress training strategies to maximise their crop’s potential. The vigorous growth of lateral branches would pair well with the screen of green (or SCrOG) method, which aims to increase the amount of light cannabis plants receive.

Similarly, yields and plant health can be improved by combining topping with the mainlining method. This is an advanced method of plant training that uses several rounds of topping to stimulate lateral branching. The lateral branches are then tied down at right angles from the soil, which will expose their nodes to light. After some vigorous growth, the branches are topped again as needed to create the desired “manifold” shape.

Big Yields and Maximising Genetics

Topping is an extremely useful tool to have in the cannabis grower’s belt. It may seem intimidating at first, but as long as the processes behind it are understood, can be carried out by growers of all levels. When combined with other cannabis cultivation techniques, growers can expect some vigorous growth and yields from their plants!

Topping cannabis plants will help reveal the potential and full extent of your genetics. Start your journey the right way by heading to Marijuana Grow Shop and perusing their excellent collection of cannabis seeds. Find robust feminised seeds, on-schedule autoflowers, and exotic regular seeds sourced from the world’s most passionate seed banks and cultivators at MGS!

Post author
Martin
Martin is a production horticulturist with experience in commercial cannabis cultivation and sustainable farming from his time with Emerald Cup Award-winning farmers Esensia Gardens in northern California's Emerald Triangle.
See more from Martin

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