Growing & HarvestFortgeschritten8 min 3 sourcesUpdated: 2026-08-03

Controlling VPD by vegetative stage

Why the VPD target window should not stay constant over the whole cycle, but shift with leaf maturity and vegetative stage.

VPD seedling

0.4–0.8 kPa

VPD vegetative stage

0.8–1.2 kPa

VPD flowering

1.2–1.6 kPa

Basics

Leaf temperature, not just air temperature

Key points

  • Young seedlings have still-underdeveloped stomatal and wax-layer control and need a lower VPD than mature plants to avoid desiccation.
  • The VPD target window should increase gradually over the cycle: from ≈ 0.4–0.8 kPa at the seedling stage up to ≈ 1.2–1.6 kPa in flowering.
  • In late flowering a compromise is needed: VPD high enough for transpiration and sugar transport, but not so high that it creates additional stress — the exact upper limit also depends on mold risk.

Note

  • Too low a VPD combined with dense canopy in late flowering measurably increases the risk of Botrytis — climate control should never be considered in isolation from canopy density.
1

Definition and classification

VPD (Vapor Pressure Deficit) describes the drying power of the air and thus the driving force for the plant's transpiration. This article covers how the sensible VPD target window shifts with the vegetative stage.

A single VPD target held constant across the whole cycle ignores that the plant's ability to regulate transpiration changes as leaves mature.

2

Scientific background

Young leaves have a still thinner cuticle (wax layer) and less precise stomatal regulation than mature leaves — at high VPD they therefore lose disproportionately more water.

As leaves mature, control over the stomata improves, which means mature plants tolerate a higher VPD and even need it for transporting sugars and nutrients.

3

VPD target values by phase

Seedling/clone: 0.4–0.8 kPa — keep low to avoid desiccation while stomatal control is still underdeveloped.

Main vegetative stage: 0.8–1.2 kPa — moderate transpiration drive for vigorous leaf mass growth.

Flowering stage: 1.2–1.6 kPa — higher drive supports nutrient and sugar transport into the buds.

Late flowering: stay at the upper edge of the target window, but at the same time don't lower relative humidity too far, so as not to additionally increase the mold risk in dense buds through swings between too dry and then humid again.

Checklist

  • Adjust the VPD target value gradually at every phase change, not abruptly
  • Use leaf temperature instead of just air temperature for the VPD calculation
  • Weigh the VPD upper limit against mold risk in late flowering, don't maximize it in isolation
4

Diagnosis for VPD mismanagement

VPD too low: weak, soft stems, slowed growth, increased mold risk from standing moisture in the canopy.

VPD too high: drooping leaves despite moist substrate, upward-curled leaf edges, burnt leaf tips — similar to nutrient burn, but without an accompanying EC anomaly.

5

Common mistakes

Using a single VPD target for the entire cycle, regardless of seedling, vegetative, or flowering stage.

Calculating VPD only from air temperature, without accounting for the often cooler leaf temperature — this leads to a systematic underestimation of the actual VPD at the leaf surface.

Maximizing VPD one-sidedly in late flowering, without considering the simultaneously increasing mold risk from excessive humidity fluctuations.

6

Advanced considerations

An infrared leaf temperature measurement instead of pure air temperature delivers a more precise, 'true' VPD and reveals local deviations under close-range light.

Some experienced growers deliberately run a slightly elevated VPD in the last 1–2 days before harvest to kick-start drying — this intervention should only be carried out with good climate control.

Frequently asked questions

Do I need to readjust the VPD target every week?
Not weekly, but the target window should be deliberately adjusted at every major phase change (seedling to vegetative stage, vegetative stage to flowering, start of late flowering).
What is more important: an absolute VPD target or stability?
Both count, but strong, frequent fluctuations are often more harmful than a slightly suboptimal but stable value — abrupt VPD jumps act as a stressor in themselves.

Sources

→ Full register
  1. 1

    Vapor Pressure Deficit and Transpiration in Controlled Environments

    Plant Physiology · 2023

    Open ↗
  2. 2

    Greenhouse Condensation Control: Understanding and Using VPD

    Ohio State University Extension (AEX-804) · 2000

    Open ↗
  3. 3

    Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2 conditions

    Physiology and Molecular Biology of Plants · 2008

    Open ↗

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Editorial note: The content is for knowledge and education. Regional law, medical questions and regulatory requirements must always be checked separately by qualified professionals.