VPD calculator

Cited targets

From the genetics.guru grow library, in the units each source used. Grades: strong and moderate are peer-reviewed; community practice is untested.

• VPD (leaf)propagation (domed cuttings)0.4–0.8 kPaExtension

  High humidity aids leafy cuttings (non-cannabis review); grower domes 85-95% RH. No cannabis VPD trial for propagation.

  2 sources

  1. Grange RI, Hand DW (1987-01). A review of the effects of atmospheric humidity on the growth of horticultural crops — Journal of Horticultural Science 62(2):125-134
  2. Dude Grows forum post 'First time cloning and not a single root on 23 cuts' (S. Bowles) (2024-03-15). Example home propagation setup: humidity dome at 85–95% RH, 80–84 °F, peat pucks
• VPD (leaf)vegetative0.8–1.2 kPaCommunity practice

  Convention; trial conditions ran ~0.95-1.3 kPa air VPD.

  2 sources

  1. Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
  2. Ahrens A, Llewellyn D, Zheng Y (2024-02-01). Longer Photoperiod Substantially Increases Indoor-Grown Cannabis’ Yield and Quality: A Study of Two High-THC Cultivars Grown under 12 h vs. 13 h Days — Plants 13(3):433
• VPD (leaf)early-mid flower1–1.5 kPaModerate

  Floor is best supported (0.25-0.62 kPa cut flower biomass 71%). High yields observed from ~0.95 to ~2.0 kPa air VPD; upper bound is convention.

  4 sources

  1. Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
  2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y (2022-09-27). Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content — Frontiers in Plant Science 13:974018
  3. Westmoreland FM, Kusuma P, Bugbee B (2021-03-23). Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids — PLOS ONE 16(3):e0248988
  4. Corredor-Perilla IC, Kwon TH, Park SH (2025-11-17). Elevated relative humidity significantly decreases cannabinoid concentrations while delaying flowering development in Cannabis sativa L. — Frontiers in Plant Science 16:1678142
• VPD (leaf)late flower1.2–1.6 kPaCommunity practice

  Convention motivated by Botrytis risk at RH >70%; ~2.0 kPa compatible with high yield in one trial.

  2 sources

  1. Mahmoud M, BenRejeb I, Punja ZK, Buirs L, Jabaji S (2023-07-01). Understanding bud rot development, caused by Botrytis cinerea, on cannabis (Cannabis sativa L.) plants grown under greenhouse conditions — Botany 101(7):200-231
  2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y (2022-09-27). Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content — Frontiers in Plant Science 13:974018
• RHpropagation (domed cuttings)70–95%Community practice

  Hemp cuttings also rooted in a 25 C / 64% RH room (dome use not stated).

  3 sources

  1. Grange RI, Hand DW (1987-01). A review of the effects of atmospheric humidity on the growth of horticultural crops — Journal of Horticultural Science 62(2):125-134
  2. Dude Grows forum post 'First time cloning and not a single root on 23 cuts' (S. Bowles) (2024-03-15). Example home propagation setup: humidity dome at 85–95% RH, 80–84 °F, peat pucks
  3. Campbell SM, Anderson SL, Brym ZT, Pearson BJ (2021-07-29). Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.) — PLOS ONE 16(7):e0249160
• RHvegetative55–70%Community practice

  Derived from VPD 0.8-1.2 kPa at 24-27 C.

  2 sources

  1. Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
  2. Ahrens A, Llewellyn D, Zheng Y (2024-02-01). Longer Photoperiod Substantially Increases Indoor-Grown Cannabis’ Yield and Quality: A Study of Two High-THC Cultivars Grown under 12 h vs. 13 h Days — Plants 13(3):433
• RHflower40–60%Moderate

  Trials ran 40-64% RH. Keep below 70% (Botrytis); 78-98% RH was severely harmful.

  5 sources

  1. Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
  2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y (2022-09-27). Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content — Frontiers in Plant Science 13:974018
  3. Westmoreland FM, Kusuma P, Bugbee B (2021-03-23). Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids — PLOS ONE 16(3):e0248988
  4. Corredor-Perilla IC, Kwon TH, Park SH (2025-11-17). Elevated relative humidity significantly decreases cannabinoid concentrations while delaying flowering development in Cannabis sativa L. — Frontiers in Plant Science 16:1678142
  5. Mahmoud M, BenRejeb I, Punja ZK, Buirs L, Jabaji S (2023-07-01). Understanding bud rot development, caused by Botrytis cinerea, on cannabis (Cannabis sativa L.) plants grown under greenhouse conditions — Botany 101(7):200-231
• RH maximum (bud-rot risk)flower≤ 70%Moderate

  Botrytis destroys inflorescences rapidly at RH >70% and 17-24 C. Apply to lights-off too.

  1 source

  1. Mahmoud M, BenRejeb I, Punja ZK, Buirs L, Jabaji S (2023-07-01). Understanding bud rot development, caused by Botrytis cinerea, on cannabis (Cannabis sativa L.) plants grown under greenhouse conditions — Botany 101(7):200-231
• leaf-air temperature offset (LED)any-2–0 °CCommunity practice

  Default -2 C is convention; model: well-watered leaves within 2 C of air under all sources; water-stressed leaves can be several degrees above air. Prefer IR measurement.

  1 source

  1. Nelson JA, Bugbee B (2015-10-08). Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes — PLOS ONE 10(10):e0138930
• leaf-air temperature offset (HPS)any-1–1 °CCommunity practice

  HPS leaves ~1.3 C warmer than LED at equal PPF (model); absolute offset is convention.

  1 source

  1. Nelson JA, Bugbee B (2015-10-08). Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes — PLOS ONE 10(10):e0138930
• leaf temperature difference LED vs HPS at equal PPFany-1.3 °C (LED minus HPS)Moderate

  Energy-balance model, typical indoor conditions; water status dominates.

  1 source

  1. Nelson JA, Bugbee B (2015-10-08). Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes — PLOS ONE 10(10):e0138930