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Temperature Stress on Cannabis

Heat Stress and Cold-Induced Damage: Protecting Marijuana Plants from the Negative Effects of Temperature

Marijuana plants tend to be fairly hardy and resilient. They will typically tolerate brief exposure to suboptimal growing conditions and will often recover on their own after suffering minor setbacks.

As with many other things, though, temperature swings can slow the growth of cannabis plants or even cause permanent damage. When exposed to light and engaging in photosynthesis, marijuana plants fare best at temperatures between 70 and 80 degrees Fahrenheit.

When they switch over to burning the fuel they made during the day, cannabis plants prefer cooler temperatures of around 50 to 60 Fahrenheit. If conditions stray too far from these ideal ranges, problems ranging from slowed growth to tissue damage can result.

Keeping a close eye on temperatures and doing everything possible to manage them will always be helpful when growing marijuana. Both indoor and outdoor growing arrangements give rise to temperature-related concerns that need to be accounted for.

Fortunately, there are always effective ways to respond when excessive heat or overly low temperatures threaten cannabis plants. Read on to learn about the most significant related issues.

Temperature Tolerance Varies

Although there some well-established guidelines, the temperature ranges that a cannabis plant will tolerate and thrive in always depend on the specifics. Some of the issues that often impact particular gardens include:

  • Root system size. – A cannabis plant with a large, expansive root system will be able to soak up more water and hold it in reserve. This will allow such a plant to shrug off heat that would otherwise endanger it. On the other hand, cannabis plants grown indoors, with their necessarily constrained root systems, tend to be significantly more sensitive to heat. Likewise, plants grown in compact containers outside not tolerate as much heat as others whose roots stretch out underground.
  • CO2 enrichment. Cannabis plants need a certain amount of warmth to carry out the all-important process of photosynthesis. When they have more carbon dioxide to work with, marijuana plants can withstand more photosynthesis-facilitating heat. This is not normally an issue when growing outdoors, but can have a significant impact on indoor gardens where additional CO2 is made available to speed up growth and improve yields.
  • Water availability. If a cannabis plant is already struggling to take up enough water, heat will exacerbate the problem. Watering in the heat of the day or while growing lights are blazing will also make it more difficult for a plant to draw in enough moisture.
  • Frequency of extremes. Whether indoors or outdoors, a healthy, properly fed cannabis plant will often withstand an occasional temperature swing without trouble. If temperatures rise too high every day or drop overly low each night, though, the plant will become less and less able to bounce back.
  • Once a cannabis plant starts flowering and developing buds, it will become more sensitive to temperature. The resources that would previously have helped buffer it against temperature swings will instead be devoted to the production of buds.
  • Some strains of cannabis are more resistant to temperature-induced stress than others. Certain ancient cannabis landraces are able to tolerate heat and cold that would devastate modern strains bred for carefully controlled indoor cultivation. When buying indica seeds, like legend OG or purple kush seed, you end up with Wide-leafed cannabis that is considered more vulnerable to heat than sativa or hybrid strains.

The Most Common Symptoms of Heat Stress and Exposure to Overly Cold Temperatures

While being aware of the impact of issues like those above will help, heat stress and cold-induced problems most often end up being identified by their characteristic symptoms. Heat stress is likely more of a concern to most growers, because overly low temperatures are only infrequently an issue indoors and tend to be recognized and proactively addressed when growing outside. Some of the most obvious and characteristic symptoms of heat stress in marijuana plants are:

  • Stretched-looking “foxtail” buds. If its buds nearest to growing lights or the sun get too hot for too long, the plant will often respond by essentially abandoning the existing growth. The flowering that subsequently appears on top will give buds a distinctively stretched-out look that growers often refer to as “foxtails.” These foxtails will be less dense and productive than the buds of plants that did not experience heat stress.
  • Wilting or drooping. Excessive heat increases the rate of evaporation, making it more difficult for a cannabis plant to hold onto the water it needs to stay healthy and grow. Wilting or drooping leaves often indicate heat stress, even if they can also suggest other problems. In extreme cases, an entire marijuana plant suffering from heat stress can even take on a wilted look.
  • Burnt leaf tips. Most often seen by indoor growers, burnt-appearing leaf tips can appear on heat-stressed plants. Because “nutrient burn” caused by over-fertilization typically produces the same effect, it will always be best to look into the situation more thoroughly when this symptom appears.
  • Yellowing and brown spots. Leaves that are just beginning to succumb to heat stress will often develop yellow patches or brown spots. As these symptoms can also suggest nutritional problems and other issues, they should not be considered independently reliable indicators of heat stress.
  • Excessively long stems. When temperatures rise too high too frequently, cannabis plants will struggle to produce new sprouts, even while their stems keep growing. Stems with unusually long, spindly-looking stems can indicate heat stress. On the other hand, cannabis plants that simply receive too much light each day often develop in the same undesirable way.

Both indoor and outdoor cannabis gardens frequently display the effects of heat stress, whether because of artificially arranged conditions or natural weather patterns. Cannabis plants can just as well suffer from excessive exposure to overly low temperatures. While that is less often an issue when growing indoors, some of the signs that it might be a problem for plants being cultivated outside are:

  • Slower growth. As temperatures drop below 70 degrees during the day, cannabis plants become less efficient at photosynthesis. Should that become common, a plant’s growth and maturation rates will decline, even if it otherwise appears healthy. That will reduce yields, both in terms of the amount of material produced by each plant and the rate of output over time.
  • Tissue damage and death. Even when persistently cold temperatures are holding back the growth of a cannabis plant, it will often remain healthy otherwise. If temperatures drop below 40 degrees Fahrenheit or so for very long at all, however, permanent damage to a plant’s tissues will often follow. A hard freeze can even kill a cannabis plant that was previously doing very well.

Taking Control of Temperature: Making Sure Your Cannabis Plants Thrive

Fortunately, virtually all temperature-related problems can be avoided or resolved by cannabis cultivators who prepare and respond appropriately. The single best way to take charge is to become proactive about monitoring temperatures–or predicting them, if growing outside.

Depending on the situation, keeping up with weather forecasts or temperature-sensor readouts will make it a lot less likely that heat stress or cold will ever have a chance to cause damage to your plants. If growing indoors and plants are displaying signs of heat stress, responses like the following can help:

  • Improved air circulation. Simply adding a fan to an indoor grow room or tent can improve air circulation enough to do away with heat stress. Installing a permanent ventilation system will remove even more unwanted heat from a room. In some cases, even propping a door open can encourage enough additional air circulation to keep heat stress at bay.
  • Cooler or more efficient lights. All grow lights produce heat, but some are less wasteful in this respect than others. Switching to a more efficient lighting technology can significantly lower the temperatures that plants experience. Air- and water-cooled lighting systems remove heat while still providing plenty of energy to cannabis Improved or better-positioned reflectors can make it possible to supply plants with all the light they need without heating them up too much.
  • More distance from lights. A common reason for stressing plants with too much heat is simply allowing them to grow too close to lights. If grow lights can be moved further away from plants without negative effects, that can be a particularly accessible way to ward off heat stress.

Heat stress can be a bit more difficult to deal with outdoors, since the environment is inherently more difficult to control. Some of the tactics that can help, though, include the use of:

  • Properly positioned misters and micro-sprayers can lower the temperatures plants experience by 20 degrees Fahrenheit or more.
  • Shade cloth. Specially designed shade cloth can be installed over stress-prone cannabis plants to keep them cooler. In a pinch, even putting up an old sheet before especially warm weather sets in can help.
  • Plants grown in containers tend to be more susceptible to heat stress than others because of their limited root systems. On the other hand, growing outdoors in containers will mean being able to easily relocate plants if hot weather is on the way. Many growers simply bring their plants indoors, but moving them to a shadier location can work just as well.

Although the problem is fairly rare, overly low temperatures indoors can typically be addressed with direct heating. A simple electric heater can be set up to warm a growing room, or a home’s existing heating system can be used, instead. Adding a CO2 generator to a grow room will also warm it up while improving the plant’s rate of photosynthesis.

Cold tends to be more of a problem for outdoor growing operations, but there are effective solutions in such cases, as well. Some of those that most often help keep the cold at bay include:

  • Patio heaters. Space heaters designed for outdoor use can elevate temperatures more than might be expected. Electric patio heaters are easy to use but can cost a fair amount to keep running. Patio heaters that burn gas or propane generally have higher output levels.
  • Simply covering cannabis plants up with a polyethylene sheet or another appropriate material will help them fight off an occasional, overnight chill.
  • Temporary relocation. As with heat stress, temporarily relocating container-based plants that are being grown outdoors can protect them from cold weather.

While excessive heat and cold can both harm cannabis plants, most growers find these dangers fairly easy to avoid. Cannabis plants are tolerant enough of temperature swings that they fare well in most common situations, and there are always effective ways to respond when related problems do arise. After reading through our comprehensive grow guide, we encourage you to checkout our ever-changing marijuana seed sale. is the seed bank USA growers turn to for reliable genetics and fantastic customer service.