The development of specific cannabinoids and compounds within a cannabis plant is its response to stress. Growers are very much aware of the importance of stressing the cannabis plant to increase THC, but may not be aware of the horticultural terminology of selectively introducing stresses called crop steering. “Growers learn lots of interesting stress techniques on the internet; often our role is to present the concept of crop steering, and how to properly introduce stress,” says Av Singh, PhD and independent cannabis consultant with Flemming & Singh Cannabis, and agronomist with Greenstar Plant Products. “The most important thing to keep in mind is that your goal as a grower is initially to create the healthiest plants possible and that means no stress.”
Crop steering
According to Av, ‘steering’ is the best way to describe the grower’s role in how a plant grows. “You are not the puppet master,” says Av. “You are just gently pushing the plant to a specific direction – there is a delicate balance that growers have to play with. It is really critical to remember that cannabinoids, terpenoids, and so on, are a plant’s response to stress. Yet, we have to remind ourselves that a plant can’t make that secondary metabolite response if you haven’t done everything right to start with -- like optimizing photosynthesis, creating the right microbial activity around the roots, and so on. You want to make sure that you have provided the plant with the necessary tools to respond to those stresses.”
Av Singh, PhD.
Av continues to explain that, during the veg period, it is of the utmost importance to provide the plant with the right nutrients, water, amount of light and temperature. “There should be no extremes at all at this stage. You want clear sailing initially, and then incrementally introduce certain stresses. We often see that growers stress the plant too early in the veg period, often unintentionally like root-bound pots, drought stress, low humidity, etc. and that leads to pre-flowering, which is definitely not desirable at all.”
“Crop steering can be defined as the introduction of appropriate stresses at the appropriate time. Irrigation is typically one of the first stresses that a grower could use. In an early veg period, you are keeping the planting media moist with short, frequent waterings. Then, to suggest to the plant that the season may be changing, you go a little dry, with longer periods without moisture, so that the plant would start experiencing minor drought stress.”
Techniques
There are many techniques under the crop steering concept. “Nutrients play a big role in crop steering because they impact plant hormones,” Av points out. “It is important to recognize it. When I design living soils, I ensure that the plants get nitrate-nitrogen early in veg, but as the plant enters the generative phase (flowering) more of the N comes from ammonium, also potassium becomes more available driving up EC, which is another stress.”
"Photo of a three-leaved cannabis plant. This is an example of a plant getting mixed signals. Some cues were steering it generative but more cues were sending it back to vegetative. Most likely differing impacts of watering, transplant stress, and photoperiod issues," Av Singh.
“More generally speaking, every environmental parameter can be a crop steering tool. In cannabis, photoperiod shift is the big one, and if it coincides with light quality shifting from less blue to more of a red spectrum, you can steer the crop more quickly into flower, perhaps saving a week in time to harvest. Temperature is also crucial, and one might start triggering some stress by increasing the differential between daytime and nighttime temperatures, mimicking the end of summer, but you want to make sure that you have no powdery mildew present because that could cause it to proliferate. CO2 is a very big stressor, and that’s why we gradually increase CO2 levels, as well as increase temperature and nutrients as you generate more growth. Any pruning technique, as well, helps reduce, in large part, humidity, which the plant understands as a signal to go more generative.”
Using the correct terminology to understand the cultivation process is paramount, according to Av. “That’s because we often place too much emphasis on creating stress, while it is critical that a very targeted stress is implemented for a reason, otherwise you just get a very weak plant. You want to grow a strong plant, and increment the stress for particular purposes.”
For more information:
Flemming & Singh Cannabis Inc.
(902) 698-0454
(506) 229-0121
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fs-cannabis.com