VPD Strategy Through the Flowering Stage
Flowering is not a single environment — it is a progression. The ideal VPD shifts as the plant transitions from stretch through bud development to ripening. Managing this progression deliberately is what separates technical growers from those who set-and-forget.
Humidity Targets to Hit Flowering VPD
| Temp | 1.0 kPa (RH) | 1.2 kPa (RH) | 1.5 kPa (RH) |
|---|---|---|---|
| 22°C | 72% | 65% | 54% |
| 24°C | 70% | 62% | 51% |
| 26°C | 67% | 59% | 48% |
| 28°C | 65% | 57% | 46% |
Approximated with -2°C leaf offset. Use the calculator above for your exact values.
Frequently Asked Questions
What VPD should I target during flowering?
During early flowering, target 1.0–1.2 kPa. As buds develop (mid-flower), push toward 1.2–1.4 kPa. In late flowering (last 2–3 weeks), 1.4–1.6 kPa is optimal to reduce mold risk and increase resin production through mild transpiration stress.
Can VPD be too high during flowering?
Yes. Above 1.6 kPa, plants enter stress mode — stomata close, photosynthesis slows, and water deficit accumulates in leaves. In extreme cases (above 2.0 kPa), tip burn, leaf curl, and early senescence occur. Keep VPD below 1.6 kPa even in late flower.
Does higher VPD during late flowering improve quality?
Evidence from commercial cultivation suggests mild VPD increase in late flower (1.3–1.6 kPa) correlates with increased trichome density and reduced botrytis risk. The theory: mild transpiration stress triggers secondary metabolite production. However, yields can drop if VPD exceeds 1.6 kPa.
How do I raise VPD during flowering?
Raise VPD by increasing temperature, decreasing humidity, or both. The most common approach is gradually reducing humidity from 55% to 45–40% over the final 3 weeks of flower while maintaining temperature at 24–27°C. This naturally pushes VPD from ~1.1 toward ~1.5 kPa.
What temperature is best during flowering for VPD?
Most flowering plants perform best at 24–27°C (75–80°F) with lights on. At 26°C and 50% RH, VPD is approximately 1.35 kPa — within the ideal flowering range. Higher temperatures increase VPD but also increase heat stress risk above 30°C.