Marijuana Heat Stress: Causes, Solution, Prevention
Marijuana plants thrive in warm growing conditions, but is too much bad for your crops? Heat stress weed is something you don’t want your cannabis to experience.
While providing cannabis plants with everything they need, we often overlook things like too much heat. Once the symptoms present themselves, you need to take action.
This process occurs on the foliage and buds of your crops, offering a droopy-looking plant with discolored leaves. Avoiding it or fixing established symptoms is your number one priority.
Let’s check out the causes, symptoms, and ways to prevent overheated weed plants.
What causes cannabis heat stress?
Temperature stress is the last thing on a grower’s mind when maintaining crops. Although most cultivars prefer warm conditions to grow to their full potential, an oversupply of heat isn’t welcome.
Heat stress relates to an unfavorable situation involving an abundance of something hot. Many cannabis strains are hardy by nature, but most don’t tolerate getting burnt by light.
How does light burn weed? It’s not about how you deliver the warmth but how much of it causes heat stress on weed plants.
The heat from various light sources encourages growth in marijuana plants. However, once the environment starts to threaten the livelihood of the crops, they begin showing symptoms.
It results in slow growth, bud quality drops, and lower yields. In a worst-case scenario, the crops may die.
Marijuana plants survive under the equitable provision of heat and light. Not too much of one thing or too little of another.
Your indoor cultivating space must be able to accommodate all equipment. Small grow rooms don’t need more than the required lights per square foot for a certain amount of plants.
Let’s go through some of the causes of heat stress.
Too many lights
Too much light for cannabis plants? Surprisingly, marijuana crops don’t appreciate an oversupply of either artificial lighting or sunlight.
While you aim to provide your crops with enough warmth and light, it’s important not to overload the grow space. It creates the ideal platform for heat stress on cannabis plants to develop.
Similar to the sun, artificial lights burn. The foliage and flower close to it absorb all the radiation, causing cannabis light burn and heat-stressed overripe buds.
Burnt leaves lead to stunted growth of the plant. As the foliage loses chlorophyll, the natural process of photosynthesis can’t effectively operate. As a result, your crops can’t convert light into energy and further into food for sustainable growth and bud production.
Low humidity levels inside a grow room significantly contribute to stressed-out cannabis plants. You’ll sometimes notice some symptoms without it being scalding.
When relative humidity in your grow rooms drops to below 50%, the air becomes hot and dry. Stomata (leaf pores) release moisture at higher rates than usual under these conditions. It leads to heat stress on weed plants, affecting their growth.
Potting soil may also lose more moisture through evaporation when the surrounding air is dry.
The aridness causes wilting of the plant while serrated leaf edges dry and tip upwards. As the presence of chlorophyll reduces in the leaves, they change color and become brown.
Humidity for growing weed varies at each growth stage. Ensure that your grow room humidity levels are on point.
Marijuana crops deal well with high temperatures within short intervals. Consistent heat provision within the growing space isn’t lucrative to their growth.
Moisture evaporates faster from the soil and plants, leaving dried-up substrates and thirsty foliage.
How hot is too hot for weed plants? Consecutive amounts of heat fixated on a particular area with temperatures exceeding 86℉ is too much for marijuana crops.
HID lights produce much more heat than LEDs, so going with the latter benefits your crops.
When air circulation is lacking inside the grow room, it’s a cause for concern and usually encourage the issue. The heat remains within the space if extractors aren’t effectively removing old air and pushing in the fresh.
The purpose of your extractor fan in an indoor setup is to clean the air that flows among your plants.
Two primary reasons to have a robust ventilating system are:
- To remove heat in the room
- Provide fresh air for photosynthesis and respiration to take place
Renewed air assists with keeping temperatures low. Refreshed air should enter the growing space every 3–5 minutes on a good day. If cannabis heat stress symptoms have beat you to it, renew that air every minute.
Remember that the smaller the grow room, the more susceptible your crops are to overheating.
Equipment problems in a grow room
Indoor crops rely on their budtenders to simulate the outside environment and make it a comfortable growing space. In addition, they depend on equipment to provide warmth, cooling aids, and sufficient airflow.
Regular maintenance checks on your grow room equipment are vital. Ensure that your air cooling and circulating systems, along with heat extractor fans, are operational on a 24-hour cycle.
If one apparatus is faulty, it affects the airflow in the room, resulting in hot weed. For example, broken thermometers won’t pick up fluctuating temperatures and humidity levels. Likewise, sufficient airflow can’t occur in the grow room if extraction fans malfunction.
It’s always wise to keep extra equipment to avoid going hours or even days without it.
Too many nutrients
Avoid cannabis nutrient burn by overfeeding your crops. Too many minerals prevent marijuana crops from regulating their temperatures.
If the plants are already dealing with excess nutrients, it becomes vulnerable to other stress issues.
Unlike an oversupply of nutrients, a lack of minerals like silicon (Si) encourages the issue.
The symptoms of heat-stressed weed
When does heat stress on cannabis plants most likely happen? The answer is: at any time throughout growth. How the symptoms present themselves depends on the stage of the crops’ development.
The severity of the injury also depends on the phase at which the symptoms arise. For example, stressed marijuana plants in the vegging stage look different from those at flowering. It’s also vital to note that different cultivars show their discomforts in various ways.
Here are some common signs you’ll notice.
The serrated tips of leaves curl upward, cupping themselves, almost as if they’re trying to create some shade by tipping over the edges. It’s how your crops tell you they’re receiving too much heat.
To avoid heat stress during the cannabis seedling stage, use a much weaker light source. Fluorescent lights are optimal as the plants don’t need ample heat yet.
Seedlings are more vulnerable than mature plants, so any ailment that occurs at this point affects the entire growth cycle.
Encountering symptoms at this point of growth, you’ll notice the following:
- Newly developed leaves are withered and pale
- Seedlings begin growing slower
- Maturation comes to a halt and may cause seedlings to die
The symptoms during the vegetative stage of marijuana plants may resemble that of calcium (Ca) deficiency. The difference between the two is how the leaves twist.
When there’s a shortage of Ca in your plants, you’ll notice the foliage twisting in various directions.
Inspect the leaves for a proper diagnosis. During the vegging phase, you’ll see the following:
- Leaf edges become dry and withered before curling up
- Dry-looking yellow and brown spots develop on the base of the leaf
- The browning may progress downward on the plant
If your plants experience extreme heat stress during flowering, it affects bud development.
The hot air allows the plants to produce airy buds (also known as foxtails) with reduced levels of THC and terpenes. The result is limited effects, flavors, and aromas.
Prevent your crops from adapting to heat stress during flowering. The damage may be irreversible since it’s the last leg of growth. Marijuana crops do more lateral stretching during this time, causing them to get closer to their light supply.
It only worsens if they’re experiencing any form of stress caused by too much light or heat.
Some marijuana plant heat stress symptoms you’ll pick up during the flowering stage are:
- The foliage seems bleached
- Leaf edges begin curling up
- Foxtail buds start to grow
- White pistils on colas instead prominent amber ones
Sometimes heat stress symptoms are similar to those of nutrient deficiencies. Know to tell the difference between a nute deficient or a heat-stressed cannabis plant.
Indoors you’ll notice cupping of leaves happening on parts closest to the light bulb. The ones further down the stem may remain unaffected because they aren’t receiving much heat radiation.
If your air circulation equipment in your growing room isn’t in top form, it may cause the entire plant to develop symptoms.
If you’re cultivating indica strains in a sweltering climate, you’ll most likely encounter weed plants with heat stress.
A great way to familiarize yourself with the problem is to look at heat stress pictures. They usually give clear indications of the cupped leaves and discoloration of some spots.
If you don’t address cannabis heat stress symptoms in time, the entire leaf surface becomes yellow before changing brown.
Fixing weed plants overheat
Set temperatures and humidity levels right to fix heat-stressed marijuana crops and wait for your plants to heal. In severe cases, you may have to remove dead foliage. To avoid the ailments from resurfacing, take all the precautionary measures.
The goal is for your plant to establish a healthy root system to allow efficient absorption of water and nutrients. It enables the crops to build a vigorous resistance to deficiencies and problems.
As best you can, prevent your crops from developing a silicon deficiency. This nutrient is vital for the flexibility of cell walls and enables plants to build resilience to heat and cold stress.
Si allows plant leaves to retain water for longer when exposed to extreme heat or drought.
Indoor setups seem to be the perfect utopia for cannabis plants to catch a heat-stress cold. Be careful, though, because they also surface on outdoor plants. Let’s see how you can deal with too much heat on your plants in both environments.
How to deal with heat stress when growing indoors
Cultivating your crops inside a grow room with indoor cannabis seeds already gives you an advantage over the ailments. You have the upper hand in controlling the environmental conditions as your crops need them.
Take note of what your summer months are like. In extreme conditions where areas experience heat waves, the airflow from outside also affects indoor air.
Invest in quality extraction fans and air conditioning equipment if you live in hot climates. Increasing circulation in your grow room removes hot air around your crops, not giving heat burn cannabis a chance.
As preventive measures, some growers avoid raising their crops during this period. Alternatively, use lights that generate less heat and provide more appliances that cool the room down.
Have enough oscillating fans around the room that evenly blows cool air above the canopies of your plants. Measure the size of your growing space and buy a fan with similar cubic feet per minute (CFM) capacity to ensure an even flow.
If your crops are too close to your light source, it’s time to increase the space between them. A comfortable distance between the plants’ canopy and the light is 12–24 inches.
LEDs produce much less heat than HIDs, making them more cannabis-friendly, especially for the home grower.
Provide the ideal temp for cannabis plants throughout growth for optimal results. Monitor temperatures using a wall thermometer to keep track of fluctuating levels so they don’t exceed 77℉.
Lower temperature and humidity levels throughout the day to maintain a consistent flow. Make use of humidifiers to keep things leveled out.
Adjusting carbon dioxide levels also help marijuana deal with heat stress.
How to deal with heat stress when growing outdoors
Managing or preventing the issue outdoors is trickier. You can’t control the environment, but you can protect your crops from unfavorable conditions.
Growing pot outdoors is the most natural way to raise your plants, but it also has limits. Intense heat waves sometimes accompany the continuous hours of sun exposure.
When fixing or preventing it from recurring, consider what your climate is like outside. Cover your growing area with a light awning material to block most of the sun’s rays.
Prevent heat stress symptoms from developing on your crops by watering cannabis plants in the morning. Avoid doing this at any time when the sun is at its peak. It warms the growing medium, which heats the roots. Hot roots mean no nutrient absorption, and a sunburned weed plant happens.
The benefit of cultivating in pots means you can move them around to shaded areas if possible. The type of pots you use affects how the roots become overheated. Clay and plastic ones retain a lot more heat than fabric ones.
Large ceramic pots keep the soil moisturized for extended periods keeping root level temperatures cool.
Add kelp extracts to your substrate. It’s a nutrient-rich seaweed supplement that enables roots to regulate moisture and temperature. Plants are also at less risk of drying out.
The best chance to avoid coming face to face with warm weed is growing heat-resistant outdoor cannabis seeds. Sativa cultivars are said to be the most resilient against too much heat.
Will cannabis plants recover from heat stress?
Completely reviving your marijuana plant depends on the severity of the damage and at which stage of growth it is.
A healthy harvest is possible if it’s early in the vegetative phase and you manage to restore the growing environment.
If your plants are well into the cannabis flowering stage and buds have fox tailed, for the most part, it’s time to accept the inevitable. At this point, closely inspect your crops to see what flowers are redeemable.
Extending the flowering stage in an effort to save the plant isn’t sustainable. It promotes heat-stressed overripe buds that have less potency and adds no value to the crops.
Some growers use supplements containing silicon dioxide (silica) to increase the plant’s ability to tolerate heat on a broader scale.
It’s all about balance
There’s no such thing as too little, or much, too hot, or cold when raising marijuana plants. All they want is their neutral sweet spot in every aspect of their growing needs. Hot weed happens.
Avoid overloading your growing space with too many lights and increase the distance between them and your crops.
Heat stress is harmful throughout growth and much more damaging in the flowering stage.
Don’t be discouraged if you lose a few heat-stressed buds. The wonderful thing about cultivating marijuana crops is that they’re forgiving, allowing you to try again. So get sativa seeds here at i49 and beat the odds of crossing paths with heat-stressed crops again.