Whether you’re doing an indoor cycle this summer, or performing routine maintenance on your outdoor crop in anticipation of the fall harvest, there a few simple tips and tricks that can quickly and easily add a 10 to 20 percent boost to your yields. Good pruning techniques and the addition of smart trellising work will not only make your plants happier and healthier, but will also reward you for your added efforts when harvest time rolls around.
Plant Puberty 101
Good pruning actually begins in the vegetative stage with the topping of cannabis plants. This technique goes by several different names, such as “pinching off,” “super-cropping” or “FIMing,” and each comes with its own unique method. Still, the goal is the same: to trigger the release or redistribution of a plant’s growth hormones—specifically auxins, the hormones responsible for growth and development in the branches, shoots, leaves and roots.
Auxins are produced primarily in the plant’s buds, leaves and shoots. These hormones stimulate the growth of plant cells, especially near the tips of shoots and roots, where the auxin concentrations are highest. Auxins also accumulate near the tops of growing shoots, causing them to continue their advance upward.
Auxins located in the main stem have the ability to slow growth in the surrounding shorter shoots. This phenomenon is known as apical dominance, and it occurs when the concentration of auxins in the main shoot is closest to those surrounding branches. As the main shoot grows up and away, the shorter shoots will begin growing and elongating once more. Apical dominance is the reason why topping a cannabis plant is so effective: When the dominant top or terminal shoot is cut or pinched off, its auxin concentration is redistributed to the lower, lateral shoots surrounding it. This causes them to grow more vigorously, while also helping to induce new growth in the form of additional top shoots that will eventually create many more top colas during flowering.
Here’s a quick guide to a few of the more prominent and successful topping techniques that lead to more robust plants and increased yields.
Topping: The removal of the top terminal shoot by cutting or slicing. This is performed once around week two of vegetative growth and then possibly again around week four (or just before flowering is triggered).
Pinching off: Basically the same technique as topping, only this one is performed using the thumb and index finger to literally pinch off the top shoot rather than using trimmers or pruning shears.
The FIM technique: Also know as “FIMing,” this technique incorporates a slight variation on the topping technique. Using small trimmer scissors, locate the top terminal shoot and, instead of cutting off the entire shoot, move down 80 percent from the top and make your cut, leaving 20 percent of the shoot still intact. The 20 percent remaining will consist of trimmed new growth (baby leaves) just above the node and will look like a freshly mown lawn.
Super-cropping: Used by Dutch growers for decades, super-cropping is the art of increasing plant growth without the removal of any plant parts. Instead, the plant is bruised (or physically altered) in order to trigger a similar response. In this scenario, a grower usually takes the main stem (or a vertical topside branch just off the main stem) and begins to “roll” it vigorously between the thumb and index finger. This will rotate the branch and cause it to pop, or blister, at the point of pressure. The branch will be injured and become weak, though you should avoid snapping it off altogether or causing it to fall limp. Instead, leave the branch at a 90-degree angle. When a branch growing vertically is bent and forced to remain horizontal, the interference in apical dominance will cause the shoots on the same axis to become stimulated and grow vertically.
Super-cropping differs from the three previous methods insofar as this technique changes previously horizontal branches into vertical-growing top colas rather than inducing new shoot growth. This is a particularly effective technique when used with horizontal trellising or “screen of green” (ScrOG)–style setups.
Ever see a grower relentlessly pruning a plant and think, “That guy is taking off way too much!” Well, there can be a method to this madness that’s often overlooked. While too much pruning can be bad for a plant, most growers are surprised by how much can be pruned without any ill effects. The truth is, pruning invigorates growth, although pruning the right amount is both an art and a science.
Experienced growers know that when pruning is used to reduce a plant’s size, the result is vigorous new growth. In late spring and early summer, outdoor growers in Northern California routinely spend one hour pruning— per plant, every day. And while these plants are basically the size of trees, that’s still a lot of pruning for each plant. But the reward is worth it.
Cannabis plants produce their fruit on the current year’s growth, flowering in the late summer and early autumn (as opposed to plants that flower in the spring, producing fruit on the previous year’s growth). As such, the pruning of cannabis plants can be done from the early vegetative stage in the spring right on into the flowering months of mid-summer. The more severe the pruning, the more vigorous the regrowth will be. Once flowering begins, however, the pruning should be scaled back and limited to the largest, darkest and oldest fan leaves, which at this point are using more energy than they can produce at the end of their life cycle. This saved energy will be redirected to the buds and helps pack on weight for harvest.
Good Pruning Strategy
Whether you’re pruning in the spring or summer, there are a few simple techniques and objectives to bear in mind. Of course, there are the objectives already discussed: pruning shoot tips to interfere with apical dominance in order to encourage lateral branching; pruning to increase or invigorate growth during the vegetative phase; and pruning (and super-cropping) to train plants to grow a certain way in order to boost yields. Here are a couple more pruning strategies to consider, all of which are geared toward increasing plant yields:
- Pruning for “crown thinning,” which aims to open up the top canopy of the plant for better light penetration. This is useful not only for large outdoor plants but also for indoor plants bunched together in a “sea of green” (SOG)–style grow. In this scenario, a grower will strategically remove certain branches, such as those that are growing inward. To avoid stress, never remove more than 25 percent of the crown.
- Conversely, “crown raising” is another pruning technique deployed by many advanced growers. This procedure involves removing the entire bottom third of the plant’s branches. This approach is also used by indoor and outdoor growers alike with the goal of redirecting all of the plant’s energy to the top colas and buds. Lower branches with small “popcorn” buds are energy suckers and don’t do much for the marketability of your buds after harvest.
- In some cases, pruning may be done in order to increase flower size—which may not necessarily increase your yield overall. Still, some growers cut off some flowering branches at the first signs of budding in order to increase the size and potency of top colas. This is usually done only for boutique or competition-grade flowers.
Savvy growers know that good pruning techniques go hand-in-hand with smart trellising practices. Typically, trellising involves using a metal or wooden framework to provide support for fruiting or climbing plants. When it comes to cannabis cultivation, the trellis can be either vertical or horizontal, and it can be made from a variety of materials.
Horizontal trellising is most commonly seen in indoor gardens, and it often takes the form of plastic mesh netting. This netting is usually laid over the garden canopy, with the plants growing up through the mesh squares (which can range in size from 3 to 5 inches). This method of trellising is particularly effective in SOG and ScrOG setups. Vertical or upright trellising is more often used in outdoor gardens, because outdoor plants are usually grown much taller and in individual plant sites. Even so, vertical trellising can be used in either indoor or outdoor grows to add support for plants, to train the direction of growth, and to increase yields.
When trellising is used in conjunction with the pruning methods discussed earlier, the result can be increased yields of 10 to 20 percent—or more. In particular, when plants are topped or FIMed, the resulting new growth—in the form of new offshoots surrounding the severed terminal node—will benefit enormously from the support and separation provided by a net trellis system. As these new shoots develop and grow, indoor growers will pull them apart and up through the mesh netting. Not only does this provide support for what will become heavy top colas, but it also helps separate and “thin out” the crown of the plant for better light penetration to the branches below.
Similarly, large outdoor plants benefit from vertical trellising or latticework in much the same way. Because these plants are usually growing in solo sites, the trelliswork is better situated vertically and surrounding the plant itself, thereby allowing the branches to grow out through the support system. Outdoor trellis systems can take many forms, including wooden or bamboo stakes fastened together with rope or wire, or wooden or metal fencing used as an encompassing framework. Perhaps the most ingenious outdoor framework is the metal-wire rebar used in construction for concrete forms. When this rebar is rolled and fastened to create a cylinder effect, it can be placed around plants while they’re still in the vegetative stage so that they can grow upward and outward through the metal latticework.
Additionally, as limbs grow and spread out, there is more airflow throughout the plant’s interior. Not only does this aid in respiration and photosynthesis, but it also helps prevent the moisture buildup that can lead to mold or botrytis. This is important for both indoor growers utilizing humid hydroponic systems and outdoor growers during the moist summer months. Still, the primary function of trellising is to provide support and stabilize the additional top and lateral shoots created via pruning. In the end, these extra limbs are what produce the added weight that will increase yields come harvest time!