Wind Burn

Wind burn is mechanical and dehydration damage from too much air hitting the same leaves for too long. It looks alarming and it is one of the least serious problems on this site, because the fix takes about a minute.

What you are seeing#

Leaves curled down and inward with the tips pointed at the floor, a shape growers call clawing. The curl is tight and the leaf often looks darker and more leathery than its neighbors.

Tips and edges go dry and brown, then crisp. In worse cases the edges look torn or ragged from being flexed thousands of times. New growth in the fan's path comes in small, crinkled or asymmetrical, because the growing tip never sat still long enough to expand evenly.

The diagnostic tell is geography. Wind burn affects only the leaves in the direct path of the fan. Follow the airflow with your hand. If the damaged leaves line up with where the air is strongest and leaves six inches to the side are perfect, that is wind burn and nothing else. A nutrient or environmental problem does not respect a fan's cone.

Why it happens#

A clip fan pointed directly at the plant at full speed, six inches away, running 24 hours a day. That is the whole cause in most cases.

Two other setups do it: an oscillating fan stuck in one position because the mechanism broke or was switched off, and an exhaust or intake vent blowing straight onto the canopy instead of moving air through the space.

Low humidity makes it much worse. A plant at 30 percent humidity with a fan on it loses water through the leaf surface faster than the roots can supply.

How to fix it#

1. Move the fan today. Point it at a tent wall, at the canopy from an angle, or just above the tops so the air rolls over the plants instead of hitting them.
2. Aim for movement, not force. Leaves should rustle and sway gently. If a leaf is flapping or bent back, the air is too strong.
3. Turn the fan speed down, or use oscillation. On most clip fans, low is plenty for a 2x2 or 2x4 tent.
4. Check the exhaust and intake. Neither should blow across the canopy at close range.
5. Raise humidity to 50 to 60 percent in veg, 45 to 50 in flower, if you have been running dry. Moving air and dry air together do far more damage than either alone.
6. Leave the damaged leaves on unless they are more than half dead. A crispy-tipped leaf still photosynthesizes.

How to tell it apart#

Versus nutrient burn. Both give brown crispy tips. Nutrient burn starts at the very tips of the leaves nearest the light and appears all over the plant regardless of airflow. Wind burn is confined to the fan's path. Stand where the fan is and look down its line: a clean boundary between damaged and undamaged leaves means wind, not nutrients.

Versus heat stress. Heat stress curls leaf edges upward into a canoe shape and concentrates on the tops closest to the light. Wind burn curls downward into a claw and follows the airflow. Put a thermometer at canopy height. Under 82F, heat is not the explanation.

Versus nitrogen toxicity. Nitrogen toxicity gives dark green, glossy, leathery leaves clawing downward across the entire plant, usually with a history of heavy feeding. If the whole plant claws, look at your feed. If one side claws, look at your fan.

How long until it looks better#

The plant stops getting worse the moment you move the fan. There is no recovery period for the plant itself, only for the leaves that already took damage.

Clawed leaves usually relax and open back up within 3 to 5 days if the damage was mild. Crisped tips do not heal and stay brown for the life of that leaf, which costs you almost nothing.

Judge it on new growth. Within 7 to 10 days new leaves should come in flat and evenly shaped. If they are still clawing a week after the fan was repositioned, stop treating it as wind burn and look at feed strength and canopy temperature instead.