Cold Stress

Cold stress affects cannabis in subtler ways than heat stress but can dramatically reduce yield and quality when sustained. Cannabis evolved in regions with significant day-night temperature variation but performs optimally with day temperatures of 75-82°F and night temperatures only 5-15°F cooler. Sustained temperatures below 60°F (15°C) during the daylight period slow plant metabolism, reduce photosynthesis efficiency, slow vegetative growth, extend flowering time by 1-3 weeks, and reduce overall yield. Below 50°F (10°C), cannabis enters near-dormancy with growth essentially stopped. Symptoms of cold stress: slowed growth visible over multiple days, purple-red anthocyanin pigmentation in leaves and stems (some growers exploit this for cosmetic appeal), darker green leaf color from chlorophyll concentration, slow water uptake leading to overwatering risk, increased susceptibility to bud rot in flowering plants because cold + humidity favors mold growth. Beneficial cold stress: deliberate temperature reduction in the final 2 weeks of flowering (dropping nights to 55-65°F) is a known technique to enhance purple color expression in strains carrying anthocyanin genetics like Granddaddy Purple, Purple Punch, and Purple Kush; the cold also slows mature trichome degradation and can preserve volatile terpenes that would otherwise evaporate at warmer temperatures. Outdoor cold management: row covers and high tunnels for late-season crops, mulching to insulate root zones, and selecting cold-hardy genetics (most ruderalis-derived autoflowers tolerate cold better than equatorial sativas). Catastrophic cold (below 32°F / 0°C frost) can kill outdoor plants overnight — northern growers must monitor first-frost dates and harvest accordingly.