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
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of heat stress before you change nutrients, watering, or the environment.
Govee Bluetooth Hygrometer
Track temperature and humidity trends instead of guessing from one reading.
Check price on AmazonBN-LINK Digital Timer
Keep light schedules consistent and prevent accidental dark-cycle interruptions.
Check price on AmazonVIVOSUN pH and TDS Meter Combo
Check root-zone pH and nutrient strength before changing a feeding plan.
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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.
Gear that prevents this problem
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