How Your Cannabis Plants Respond to Stress, Good and Bad
In cannabis cultivation, as in life, there are two types of stress—good and bad.
Good stress causes the cannabis plant to work harder to achieve a desirable goal (larger buds, anyone?).
Bad stress is counterproductive to growth and could ultimately kill the plant. When growing cannabis, it is important to maximize the use of good stress and minimize the introduction of bad stress.
Email Newsletter
Join thousands of other growers who are already receiving our monthly newsletter.
Bad Stress for Cannabis
Some plant stressors are counterproductive to growth as they inhibit the plants’ ability to absorb light for photosynthesis, constrain appropriate amounts of leaf transpiration, increase susceptibility to pest/disease attack, and potentially cause the plants to develop genetic abnormalities (hermaphroditism); all of which could devastate an entire flower crop.
Cannabis plants require particular lighting levels during the propagation stage, vegetative stage, and blooming stage. | Source: Gleti/Shutterstock
Light
When flowering, cannabis plants are very susceptible to stress from interruptions in the light cycle. Even a red indicator light on a camera can cause plants to become hermaphroditic. As such, it is crucial to maintain complete darkness during the entire lights off cycle.
Because commercial operations require cameras in every room of the grow, look for cameras and other emergency lights that have green indicator lights instead of red and then securely cover the light with a piece of electrical tape.
Read also: Try This Highly Recommended Cannabis Lighting Schedule
The photoperiod of cannabis plants is largely unaffected by low intensity green light, making it the better choice of light source for dark cycle work lights and indicators.
Now, don’t mistake the previous statement as, “Cannabis plants don’t use green light for photosynthesis”. They very much do. However, there are different chemical processes within the plant that are at play when it comes to photoperiodism.
If work must be completed during the lights off cycle, only use a low power green LED for a light source. When no work is being completed in the flower room, the space should be completely dark and tested regularly to verify that no new light leaks have developed.
Temperature
Within the conventional indoor grow environment, heat is typically much more of a negative stressor to cannabis plants than cold.
Cannabis plants grown indoors aren’t usually exposed to temperatures below 50°F, so seeing stresses caused by plants getting too cold is an uncommon event.
However, when ambient conditions rise above 85°F, the plants start to alter their growth patterns to accommodate a higher rate of transpiration to keep the plant cool.
This altered growth puts extra energy into growing more plant stem, ultimately resulting in a lanky plant without the desired flower mass yield and essential oil production. At extremely high temperatures, photosynthesis can cease entirely and maturation of the crop will certainly be delayed.
Keeping the temperature and humidity of the room at an appropriate level throughout the day is crucial to maintaining an efficient grow.
Read also: The Best Temperatures for an Indoor Grow Room
Inadequate airflow can result in humidity levels becoming too high and growing conditions that get too hot. | Source: Cactuss/Shutterstock
Good Stress for Cannabis
There are a variety of good types of stress that can be introduced throughout the growing cycle. Exposing cannabis plants to good stress will result in robust plants that are more likely to produce more resin and larger buds. The best plants are the ones that not only survive doses of good stress, but actually thrive on it. To ensure you are growing the best plants, it is important to cull plants at each stage of growth.
Air Circulation
Using air circulation is the most common way of stressing plants that most people already incorporate in their room for other reasons. By using an oscillating fan to keep young plants moving with forced air, you are, in effect, constantly providing small stresses to the stem of the plant which help the stem become thick and robust more quickly than if forced air is not used.
Plant Training
Plant training is the process of managing plant growth using various levels of applied stresses to manipulate the plant shape and size. These stressors alter growth by changing the plants’ nutrient distribution pathways, modulating metabolic rates, and by physically spreading the plant out laterally, making it easier to maintain an even canopy.
There are several ways of achieving this end. Some may seem extreme, but they’re worth experimenting with if you haven’t already.
Low-stress training can be used to encourage plants to grow horizontally, which often allows for stronger overall growth and maximizing your growing area. | Source: content_creator/Shutterstock
Low-Stress Training (LST) is the practice of using small amounts of constant force to encourage plant branch growth in the growers’ chosen direction while opening up lower nodes to higher light intensity.
Applying this stress throughout the vegetative growth phase will provide thick stem growth, which will produce additional nutrient and water delivery capabilities during flowering. This technique is very good for increasing yield per plant while keeping the overall plant height to a minimum. Screen of Green (ScrOG) trellising, tomato cages, and using bamboo stakes (AKA, sticking and spreading) are all great methods of applying this type of gentle stress.
Super-cropping is the method of basically breaking your plants. While this may sound extreme, it will increase your yield if done correctly. Super-cropping is the method of taking growth that is too tall for the grower’s liking and bending it in the desired direction of growth until the stem’s inside structure breaks. The intent is to break the inside while leaving the outer structure free from damage.
Read also: Topping and Low-Stress Cannabis Training
After a few days, you’ll notice a knuckle forming at the bend; this is a good thing. This stress increases the plants ability to deliver nutrients to the top nodes on that branch while opening up the lower branches to more light.
Topping is the most common plant control technique used in cannabis gardening. This process involves clipping off the very top shoot from the topmost plant branch(es). In doing this, the top node splits into two shoots.
This can be done multiple times through the vegetative phase to maintain the desired canopy height. For some cannabis strains, this technique will produce a nice bushy structure that provides a higher yield potential per plant. Remember, this technique should be used during vegetative growth only and is not appropriate to use during flower growth.
Lollipoping is another way of directing plant hormones to the branches or nodes of interest through defoliation. In this technique, undergrowth is periodically stripped away with the intention of pushing robust new growth to the top of the branches.
During vegetative growth, this practice will allow the grower to direct growth in the direction of their choosing by stretching branches into the desired position on the canopy.
During flowering, this technique is used to discourage ‘popcorn buds’—small underdeveloped flowers that are typically not marketable for flower sales—by directing growth to the top cola on each branch. It’s recommended to take advantage of this technique before placing the plant into a flowering state and between two to three weeks after the 12/12 photoperiod has been applied, depending on the genetics of the plant.
Cold temperatures can produce unique colors in certain cannabis strains. | Source: pancakenap420/Shutterstock
Cold Temperatures
While it may seem like a bad idea to allow cannabis plants to get cold given their ideal growing climate, it can actually be beneficial to allow the room to cool down to between 50 and 60℉ at night during the last two weeks of the flower cycle. A sequence of warm days (lights on) and cool nights (lights off) towards the end of growth mimics the natural growth cycle of cannabis plants.
Read also: 5 Flowering Stage Tips for Cannabis
In fact, many cannabis genetics naturally flower in the colder months. Running colder temperatures boosts the plants’ metabolic system, resulting in more resin production and a larger range of aesthetically appealing flower colors. Purple pistils are a result of cool nights at the end of a flower cycle combined with the plants’ genetic predisposition for producing purple colors.
Simulate a Drought
Drought stress is another method that is commonly used to encourage accelerated growth rates. If applied correctly, simulating a drought causes plants to react by increasing root growth rates as it prepares for supply shortages. At the same time, this increases the levels of available oxygen to the root zone. Advanced growers can push their plants’ growth much harder using this method.
However, be careful as too much of this stress is definitely a bad thing. You don’t want to see wilting plants or have the plants develop an embolism while you’re in the middle of a flowering program. Become comfortable with this technique on the small scale prior to attempting to incorporate it into a large cannabis production process.
Final Thoughts
As you can see, applied stresses can affect the plant in many ways; both good and bad. It’s up to the grower to know how to take advantage of the positive while constantly keeping negative stressors at bay.
If used properly, the above methods will help you increase your facilities’ yield per watt and yield per square foot figures. All of these methods have been proven to aid growth in one way or another on their own; however, when you learn how to use them in concert with one another, you’ll start to see your garden become truly magical.
Read next: Plant Support: How to Manage Your Cannabis Garden Canopy
