Healthy and Unhealthy Cannabis Plant Stressors

Healthy and Unhealthy Cannabis Plant Stressors

Posted by Celia Daly on March 4, 2015 12:00 am
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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?); whereas, bad stress is counterproductive to growth and could ultimately kill the plant. As such, when growing cannabis in a commercial setting, it is important to maximize the use of good stress and minimize the introduction of bad stress.

Bad Stress

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.


Whensad cannabis plant 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 hermaphrodite. As such, it is crucial to maintain complete darkness during the entire lights off cycle. Because it is required to have 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. 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”, as 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, use a low power green LED for a light source only.  When no work is being completed in the flower room, the room should be completely dark and tested regularly to verify that no new light leaks have developed.


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 stresses seen from plants getting too cold is an uncommon event.  However, when ambient conditions are taken above 85°F, the plant starts to alter its growth pattern to accommodate for a higher rate of transpiration in order to keep the plant cool. This altered growth puts more 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.

Good Stress

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 can not only survive doses of good stress, but can actually thrive on it.  In order to ensure you are growing the best plants, it is important to utilize plant culling 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 actually 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 through the use of various levels of applied stresses in order for the grower to manipulate the plant shape and size to his or her liking.  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, however, they’re worth experimenting with if you haven’t already.

Low-Stress-Training (LST):  Low-stress-training 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/water delivery capabilities during flowering.  This technique is very good for increasing yield per plant while keeping the overall plant height to a minimum.  ScrOG (Screen of Green) trellising, tomato cages, and using bamboo stakes (sticking-and-spreading) are all great methods of applying this type of gentle stress.

Super-cropping: Break your plants!  While this may sound extreme, if done correctly it will increase your yield.  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 structure while leaving outer structure free from damage.  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:  Topping is the most common plant control technique used in commercial cannabis gardening.  This process involves clipping off the very top shoot from the topmost plant branch(es).  In doing this, the top node splits from one shoot, into two.  This can be done multiple times through the vegetative growth phase as needed to maintain the desired canopy height.  For some cannabis strains, this technique will produce a nice bushy structure providing a higher yield potential per plant.  This technique should be used during vegetative growth only and is not appropriate to use during flower growth.

Lollipopping:  Lollipopping is another way of directing plant hormones to the branches or nodes of interest through defoliation.  In this technique, undergrowth is periodically striped away with the intention of pushing robust new growth to the top of the branches.  Much like the above techniques, 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 2-3 weeks after the 12/12 photoperiod has been applied depending on the genetics of the plant.

Cold Temperatures

pink cannabis pistolsWhile it may seem like a bad idea to allow cannabis plants to get cold given their ideal growing climate, during the last two weeks of the flower cycle, it can actually be beneficial to allow the room to cool down to between 50℉ and 60℉ at night.  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 – 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. The pronounced purple pistols in the picture to the left 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 while at the same time increasing the levels of available oxygen to the root zone.  Advanced growers are able to push their plants’ growth much harder using this method. However, be careful –  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 into a commercial cannabis production process.

As you can see, applied stresses can affect the plant in many ways; both good and bad.  Its up to the grower to know how to take advantage of them when advantageous 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.

Topics: Cannabis Basics, cannabis cultivation, climate control, featured, growing, lighting, stress

2 responses to “Healthy and Unhealthy Cannabis Plant Stressors”

  1. Cc says:

    Growing Afghan Kush in a tent. The plants seem healthy but I notice that on the stems (where the branches armpit) I have very red or purple nodules there. They look like they’re almost a purple wet ball of resin but they are hard. Just one on each of several of the branches. The other plants are also doing just fine but a different variety and all green and healthy. The Afghan have striped stems and branches.

  2. These are helpful to all cannabis growers around. I am glad that there are articles like these which provides a good information. thank you for spreading awareness and for spreading this.

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