You are hereHeat Stress
Problem: Your cannabis plant can only withstand a certain amount of heat and light. After a certain point, your cannabis will start exhibiting signs of stress on the leaves near the sources of light and/or heat. Your leaves will get yellow or brown brown spotting and may appear generally burnt in places when there's too much light.
Cannabis will also display heat stress when grown outdoors in hot, dry weather, especially when not given enough water.
When the heat gets too high, the edges of the leaves will begin to curl up and the leaves will begin to "cup."
Solution: Get a way to monitor temperature. Control heat by whatever means necessary using the steps outlined below.
Indoors, find a way to lower the temperature and/or increase the circulation in the grow room or grow area if heat is the problem. Having a small fan blowing over the tops of your plants will help prevent hot spots from forming directly under your grow lights.
You may consider removing grow lights further away from the tops of the plants.
When learning how to grow cannabis, it's best to try to keep things at a comfortable room temperature at all times for optimal growth. If it's too hot for you, it's probably too hot for your plants.
When cannabis plants are recovering from heat shock, some growers recommend using seaweed extract (often available as a convenient liquid fertilizer) to help plants recover from the stress and possible even protect plants from heat stress in the future.
Many indoor setups will require that you vent out hot air using a fan and/or an exhaust system. By creating good suction with an efficient exhaust system and adding a carbon scrubber, you can also pretty much scrub all smells from the grow room. Learn more about controlling odors in the grow room.
An oscillating fan will circulate air in the room as well as provide a gentle breeze for your plants, and a small one will cost less than $20.
Outdoors, you have less options to reduce heat during a heat wave, but you are able to monitor your local weather via weather forecasts.
It is possible to partially shield your plants when you know the temperature is going to get hot. You can also adjust your watering schedule to make sure plants at least have plenty of water.
Some things to try when you know the weather outside is going to be hot or dry:
- water plants in the evening or early morning to help prevent water evaporation during the hottest hours
- kelp extract for roots - provide a small amount of liquid fertilizer that contains seaweed kelp extract (can help protect against heat stress)
- increase shade to reduce the heat experienced by plants - you can use an old sheet or other cloth as a short term solution, or get a profesionally made "Sun Shade Sail" which is made particularly to create shade outdoors. It's important to remember that giving plants shade for more than a few days will make them less "hardened" to the sun, and you may need to reintroduce full sunlight back slowly to prevent them from getting shocked from the light intensity
- move potted plants - luckily with potted plants, it's usually easier to move them out of direct sunlight during a heat wave
- take extra good care of heat-stressed plants - when cannabis plants appear heat-stressed, try to baby them as best you can, and offer shade during the hottest days.
When growing cannabis outdoors, it can often take a few weeks for plant to recover after a hot or dry spell, so prevention is the best medicine for outdoor plants.