In the process of growing cannabis, we often experience cannabis heat stress. Cannabis can only withstand a certain amount of heat and light and beyond what they can handle will manifest a certain amount of stress on the plant creating spots on the leaves and making them curl and turn yellow. Today we take a closer look at cannabis heat stress.
When is Cannabis Heat Stress Likely?
Seedling Stage: Heat stress is less common in the seedling stage, but it does happen occasionally. Heat-stressed seedlings will look pale and wilted and grow slowly. If your seedlings are lucky enough to escape all this and grow successfully, they will also become very fragile and breakable, and will be strongly stimulated by slight changes in the external environment. This way your plants will be very unhealthy even if they grow.
Vegetative Stage: Heat stress is easy to appears in this stage and the performance of plants is more typical. The leaves will turn dry, the edges will curl and wilt, there will be yellow-brown spots on the leaves, and there will be burn marks on the tips. Make sure you examine the leaves carefully because these signs are very similar to a calcium deficiency.
Flowering Stage: In addition to the leaves appearing to be bleached or yellowed and curled, heat stress during the flowering stage is manifested by the appearance of an excessive number of white pistils and the growth of long, airy foxtail buds.
Why Your Plant is Experiencing Heat Stress?
The biggest reason is that your grow lights are probably too close to your plants. We have discussed this issue in previous articles so be sure to check those out!
In addition to this, there are a few factors that can cause heat stress.
Too Much Light
It’s easy to think that more light is better when we first grow, because light directly affects the yield of cannabis. But actually too much light can cause heat stress. If your grow lights have a PPFD level of over 1300-1500 without supplemental CO2, then your plants will definitely have problems.
Before buying your grow lights, ask the manufacturer how high they should hang and find the right wattage for your grow room.
Ventilation is very important to our grow tents. It not only reduces heat but also provides fresh air inside the tent so that plants can carry out photosynthesis. So, we need to set a suitable fan for the tent.
When our plants are under heat stress, the plants themselves fight for better health. (Not only heat stress, but almost all external pressures, plants have a certain degree of self-healing ability, provided that the problem is not serious.) Your cannabis will resist high temperature through transpiration, and transpiration cannot occur without enough of water. If your grow room humidity is too low, it is difficult for plants to transpire and heat stress is difficult to relieve.
How to Fix Heat Stress
- Use LED grow lights that generate less heat than regular grow lights and hang them properly in the grow room.
- Keep the roots cool. Avoid direct light onto the roots. Try adding seaweed kelp extract to your plants, which contains minerals that can be used to prevent heat stress.
- Water your plants in the morning and evening. Water when the lights have just been turned on or off, and avoid watering at the hottest times when water evaporates too quickly meaning plants won’t have enough water to withstand heat stress.
- Proper ventilation. Your fan should renew the air inside the tent completely at least every 5 minutes. Choose a fan with the aCFM that matches the size of your tent. If possible, you can set up multiple fans in your tent, especially if you set clip-on fans near the leaves of plants—this works well to dissipate heat.
Heat stress is a widespread problem when we grow cannabis, but generally heat stress doesn’t have very serious consequences because you can always find out that your grow room is overheating very quickly. Prevention is better than cure for any problem and providing a perfect environment for your plants to control is always better than finding a problem and then fixing it. If you would like to learn more about planting, please subscribe to our newsletter!
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You may also like articles about cannabis heat stress:
Light Burn and Light Stress in Cannabis Plants
The Easy Way to Fix Nutrient Burn