Heat Stress

Upper canopy leaves cup upward (taco shape), often with crispy edges or yellowing tips. Most indoor crops perform best at 22-28 C with lights on. Above 30 C stomata close, photorespiration rises, transpiration outruns root uptake, and growth and yield drop sharply. With CO2 enrichment the optimum can shift to 28-30 C.

What usually causes it

• Lights-on temperature above 28-30 C at canopy level
• Lamp too close generating radiant heat
• Insufficient extraction or fresh-air exchange
• High VPD (low RH at high temperature) overdriving transpiration

Related product categories

• Climate & Ventilation
• Lighting

Terms worth knowing

• VPD (Vapour Pressure Deficit)

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