Temp & Humidity for Vegetative VPD
| Temp | RH for 0.8 kPa | RH for 1.0 kPa | RH for 1.2 kPa |
|---|---|---|---|
| 20°C | 85% | 79% | 73% |
| 22°C | 82% | 76% | 69% |
| 24°C | 79% | 72% | 65% |
| 26°C | 76% | 69% | 62% |
| 28°C | 73% | 66% | 59% |
Calculated with -2°C leaf offset. Use calculator for exact values.
Frequently Asked Questions
What is the ideal VPD for vegetative growth?
The ideal VPD for vegetative growth is 0.8–1.2 kPa, with 1.0 kPa as the optimal target. At this range, stomata remain open, photosynthesis operates at maximum efficiency, and nutrient uptake through transpiration is vigorous without causing water stress.
What temperature and humidity hits vegetative VPD?
At 24°C (75°F), you need approximately 60–65% RH to hit 1.0 kPa VPD. At 26°C (79°F), target 62–68% RH. These are comfortable, achievable conditions without specialized equipment in most climates.
How does VPD affect plant growth rate in veg?
VPD directly controls transpiration rate, which drives nutrient delivery to growing tissue. At optimal VPD (0.8–1.2 kPa), nutrient solution moves freely from roots to leaf tips. Below 0.6 kPa, nutrient transport slows and growth stalls. Above 1.3 kPa during veg, stomata partially close, reducing CO₂ uptake and photosynthesis rate.
Should VPD be the same at lights-on and lights-off?
No. At lights-off, temperature typically drops 4–8°C, which causes VPD to fall sharply. If your lights-on VPD is 1.0 kPa at 26°C/62% RH, your lights-off VPD at 20°C may drop to 0.5 kPa at the same humidity. This is generally acceptable — plants transpire less in the dark. The risk is that very low VPD at night increases condensation and mold risk.
Can I use VPD during vegetative in coco or soil?
Yes — VPD applies to any growing medium because it describes the air environment around leaves, not the root environment. Coco and soil growers benefit equally from managing VPD, particularly to prevent over- or under-watering decisions driven by plant appearance (wilting can signal both overwatering and high VPD stress).