Environmental StressSerious
Heat Stress in Cannabis
Cannabis stops growing efficiently above 82°F. Prolonged heat causes stretchy, lanky plants, tacoed leaves, and foxtailing in flower.
What it looks like
- ●Leaves curling UP (tacoing)
- ●Yellow or white tips on upper leaves
- ●Stretched, lanky growth
- ●Foxtailing during flower (new growth from buds)
- ●Slow growth despite perfect nutes and light
Quick diagnostic checks
1Raise the light as first action
2Crank exhaust fan
3Light-on-at-night schedule beats summer heat
Causes ranked by likelihood
1. Inadequate ventilation
Most commonSigns
- ●Undersized exhaust fan
- ●Tent temp 5°F+ above room temp
- ●No intake fan
Fix
- ✓Match fan to tent size: 4x4 needs ~200 CFM
- ✓Add a passive or active intake
- ✓Exhaust should replace tent air every 1-3 minutes
Recommended products
AC Infinity CLOUDLINE T4
Smart 4" exhaust with temp-triggered speed
2. Light too close to canopy
CommonSigns
- ●Canopy temp 8°F+ above floor temp
- ●Upper leaves tacoing
Fix
- ✓Raise light 4-6 inches
- ✓Dim if possible
3. Summer heat in unconditioned space
CommonSigns
- ●Grow space has no AC
- ●Temps 85°F+ all day
Fix
- ✓Run lights at NIGHT when it's cooler
- ✓Add AC/dehumidifier combo
⚠️When to worry
Sustained 85°F+ in flower causes foxtailing and 20%+ yield loss. Fix within a week.
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