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Heat and Light 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.
If you directly touch a plant's leaves with the lights, you will also leave "burns" if the bulbs were hot when they touched the leaves.
When the heat gets too high, the edges of the serrated leaves will begin to curl up even if there are no burns or other signs of light stress.
Solution: 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.
If your marijuana plants are just getting too much light, try removing some of the lights or moving your lights further away from the tops of the plants.
When learning how to weed, 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.