Heat Stress: Tacoing Leaves and What to Do
Heat stress shows up first at the top of the plant, closest to the light, and it looks distinct enough that you can diagnose it across the room.
The signs
Leaf edges curling upward into a taco shape, dry crispy margins, upward-cupping leaves, and in flower, foxtailing on the tops. Lower canopy usually looks fine.
Immediate relief
Dim the light by 20%, raise it a few inches, increase exhaust speed, and open a lower intake flap. Those four changes take two minutes and usually drop canopy temp several degrees.
Permanent fixes
Run lights during the cool part of the day, upgrade the exhaust fan, duct exhaust out of the room entirely, or condition the room air with an AC unit.
Do not confuse with light burn
Light burn bleaches tops toward white. Heat stress curls and crisps them while the color stays green. They often occur together.
Frequently asked questions
- What canopy temperature is too high?
- Sustained above 86°F causes stress, and above 90°F causes real damage and terpene loss.