Environmental StressSerious
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
1Keep indoor grow 65-80°F at all times
2Cover outdoor plants if frost is forecasted
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.
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