VibeLux - Advanced Controlled Environment Agriculture Platform

Humidity Deficit & Crop Steering

Steer vegetative/generative balance on Humidity Deficit (HD) — the grams of water the air can still absorb before saturation. Expressed in g/kg of dry air, the temperature-independent metric Dutch growers steer on (plus g/m³ and VPD for cross-reference).

Air temperature (°C)

Relative humidity (%)

Elevation (m)

Adjusts air pressure

Air exchanges (per hour)

Over the crop (for max-HD guidance)

Humidity Deficit

4.8 g/kg

Neutral / balanced

0GenerativeNeutralVegetativeExhaustion12+

A balanced deficit. Around 5 g/kg is a common generative target in semi-closed glasshouses — enough transpiration to keep the plant active without over-driving leaf growth.

At 6 air-changes/hour over the crop, keep HD below ≈ 6.7 g/kg (faster air movement strips more moisture from the leaf, so the safe ceiling drops).

5.4 g/m³

Humidity deficit (volumetric)

Many climate computers

0.75 kPa

Vapor pressure deficit

Air VPD (rest-of-world)

14.0 g/kg

Actual moisture (GH)

18.9 g/kg

Saturation (AH = GH + HD)

Steering guideline (g/kg)

Generative ≤ 3 — humid, assimilates to fruit

Neutral 3–5 — ~5 is a common target

Vegetative 5–8 — more leaf growth

Exhaustion > 8 — yield loss risk

A LOW HD (humid air) is a generative impulse; a HIGH HD drives transpiration and leaf growth (vegetative) and, if too high, exhaustion. Guideline thresholds and the HD-vs-air-exchange ceiling are adapted from Godfried Dol, How to Grow in a Modular Glasshouse (2020), ch. 4. Treat as a starting point and tune to your crop and stage.

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