How to use pruning and trellising for big advantages.
Story and photos by Nico Escondido
There are many ways to achieve bigger yields in your garden. Some methods focus on feeding programs, others on system type or lighting setup. However, one of the best ways to improve yields is to use simple plant science and biology to allow a more natural increase in production.
Understanding the physiology of cannabis plants can be beneficial not only for the quality of the final product, but also for its quantity. This means you won’t have to sacrifice one for the other, which can sometimes be an issue when choosing to increase yields via chemicals or technology. What follows is a basic breakdown of a two-part method for improving yields that focuses on two relatively simple gardening techniques: pruning and trellising. Together, they can provide a powerful tool for increasing yields for everyone from the home grower to the commercial cultivator.
The Science of Pruning Cannabis
It’s often been said, and it’s actually quite true – pruning is both an art and a science. The art aspect is easily appreciated: Pruning can infuse creativity into your gardening experience and change the overall aesthetics of your garden, plants and buds for the better. But for our purposes here, the focus is on the science of pruning, specifically understanding the hows and whys.
First, let’s start with a warning: Cutting is an irreversible operation. Therefore, it’s better to start by cutting too little rather than too much, especially if you’re new to the practice. Remember, you can always go back and cut more, but it’s a lot tougher (though not impossible) to reattach broken stems or branches.
Pruning creates a bushing effect and causes a need for trellising.
That being said, the first concept we need to address when learning about pruning is apical dominance. This occurs in the terminal or topmost shoot of a plant (though it’s also closely linked with the center or main stem or trunk), and it’s what guides the upward direction of the plant’s growth. Apical dominance is governed by the production of plant hormones (auxins) that are developed in the terminal shoot, which inhibit the growth of other lateral shoots below. However, with the removal of this top-most dominant shoot, there’s a decrease of certain auxins throughout the plant, which allows these lateral shoots to produce new, vigorous growth. This type of pruning is usually known as “topping” or “pinching off,” in reference to the various ways for removing the terminal shoot.
Pruning has two main objectives: controlling the direction of growth and encouraging vigorous new growth. By removing apical dominance, you will cause the plant to begin directing its growth to the highest lateral shoots – in cannabis, usually the two main side nodes directly below the center shoot. These two lateral shoots now become invigorated and will rapidly become the new main top shoots of the plant. And this is where trellising begins to come in handy.
When it comes to trellising, it’s probably accurate to say that it involves more art than science. Still, the practice does involve a fair amount of technical execution.
A trellis system is simply a frame or structure of latticing (crossed strips) that is used to support growing plants. Indoor growers may be familiar with the term “screen of green” (ScrOG), a variation of the “sea of green” (SOG) technique. The screen or netting used in ScrOG – which is laid over the top canopy of a garden, with the branches weaved through it during growth – is a form of trellising; others may include interlocking strips of wood or metal. Sometimes a trellis cuts through or over a plant in many directions; other times, only a few cross-sections are used and the branches are pulled back and tied off.
The early stages of veg is when topping should occur and trellis training begins.
Once we examine the effects of pruning, it becomes quite clear why a trellis can prove very useful in the garden. Now imagine if a cannabis plant was repeatedly topped during its vegetative stage. (Note: Any topping, pinching off or FIMing of the plants should only be done during the vegetative stage.) The ensuing effect would be an extreme bushing, with many new top shoots developing. This is because, after the first topping, there is no longer a single, dominant terminal shot, so that each time a new top lateral shoot is removed, the two nodes or branches directly below it will begin to grow vigorously as if they were the main terminal shoots. Each time this process is repeated moving down the plant, more and more “main” shoots will develop. However, these shoots will need extra support, since they are lateral branches and don’t have the structural support that a single, dominant center shoot would have had.
Next, we need to understand how trellising can aid in increasing plant yields. The trellis is used as the plant’s support system for all the new top colas that will be forming. As each top shoot is pinched off, the new growth that develops directly beneath it needs to be trained as it grows – i.e., pulled up or woven through the trellis. This is why netting (with approximately 6" x 6" squares) is often one of the best methods for trellising, as it’s easy to spread out over the tops of plants or the garden canopy, and it’s also easily attached to the corner and side posts that provide the support strength needed.
Four weeks into flowering, the results of effective topping, and the need for trellising, become apparent.
When using a trellis of any kind, it’s important to pull the plant’s branches apart to give them as much lateral separation as possible. This not only allows them room to grow, but it also creates better light penetration as well as air (and CO2) circulation throughout the plant. As the branches are pulled out, the colas or shoot tips should be trained to grow vertically (i.e., up). The natural tendency of the plant is to grow toward the light, so when the branches are trained horizontally, the plant will try to correct this: Buds in the leaf axis will begin to grow vertically, though in most cases this will affect just the tip or cola of the branch. But in some systems where the branches are woven horizontally through a trellis at length, the result can be many top cola formations along the same lateral branch. This system will require increased spacing between the individual plant sites below the canopy and also possibly a larger garden space overall, but it can also greatly increase yields through supercharged production from each plant.
More Pruning Points and Trellis Tips
Maximizing a plant’s potential for yield is not an easy task: It requires a lot of time and attention paid to each plant in the garden, as well as increased pruning and maintenance. When using a trellis system, the need for pruning doesn’t end after topping the plant a few times – in fact, it increases.
As the plants bush out and more and more tops are woven up through the trellis, it’s important to trim off the excess interior leaves and lower shoots, which will eat up plant energy and block light and air movement. Big fan leaves as well as tiny offshoots near the bottom are consuming more plant food than they’re helping to create; this energy can be more usefully directed to the developing colas and flowers higher up the plant.
Trellising not only structurally supports new top growth, but also aids in separating branches and creating better light penetration.
Mold or botrytis can also become a problem when cannabis plants are pruned to grow round and bushy. Moisture and humidity increase within the plant as new offshoots and leaf vegetation develop and lock moisture within the plant’s interior. Clearing out older and bigger leaves close to the main stem helps prevent mold from forming.
Certain trellis types are especially effective at promoting increased yields, while also lending themselves to easy plant maintenance and preventive pruning measures. Indoors, the aforementioned string netting is a good choice, as are bamboo shoots, which are non- abrasive and sturdy, and which many gardeners use to create their own simple latticework with pull ties. (However, when using any type of sticks or rods, be very careful when inserting them into the medium container so as to not damage plant roots.) Outdoors, vertical or upright trellis systems are often deployed, since there’s usually more space to work with. Wooden frames or wire cylinders placed around the plants make excellent choices for branch separators and support.
Whichever direction you choose, remember that tying branches can be a risky proceeding. It’s also worth noting that even after the vegetative stage (and the topping of plants) comes to an end, the plants will still grow up to another two-thirds in size during flowering! Which is why it’s best to design a trellis system that gives your plants the leeway to expand and develop as needed. After all, stressing your plants and inhibiting their growth runs counter to the objective here, which is simply to maximize each plant’s potential and increase our garden yields.