Cold Shock in Cannabis
Cannabis stops growing efficiently below 65°F. Prolonged cold causes purple stems, slow growth, and weak plants — and frost kills outright.
What it looks like
- ●Slow or stopped growth
- ●Purple stems and leaf petioles
- ●Leaves may look "tight" and small
- ●Outdoor: black spots after cold nights
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of cold shock 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 AmazonAC Infinity CLOUDLINE T4
Automate airflow to manage heat, humidity, and mold pressure.
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Causes ranked by likelihood
1. Basement or garage grow in winter
Most commonSigns
- ●Tent temp below 65°F at night
Fix
- ✓Add a small ceramic heater with thermostat
- ✓Insulate the grow space
- ✓Keep tent above 65°F minimum
2. Outdoor cold snap
CommonSigns
- ●Overnight temps near or below freezing
Fix
- ✓Cover plants with a frost cloth
- ✓Bring small pots indoors
- ✓Plan outdoor grow with last/first frost dates
⚠️When to worry
Frost (below 32°F) can kill a plant outright. Cold stress over weeks cuts yield.
Gear that prevents this problem
The right equipment stops most grow problems before they start. Start here:
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