Quick answer: Greenhouse sweet peppers are a warm crop: typical targets are about 21–25 °C by day and 18–20 °C at night, with 60–80 % RH (roughly 0.5–1.0 kPa VPD) during active growth. Humidity matters in both directions: long wet nights favour Botrytis on stems, flowers and fruit; very dry air with warm temperatures stresses plants and can contribute to blossom-end rot; and pepper powdery mildew can develop at moderate humidity on dry leaves. Keep nights warm enough and below saturation, keep air moving through the dense canopy, and dehumidify when venting would lose too much heat.
Quick answer (typical ranges; follow cultivar guidance)
- Day 21–25 °C; night 18–20 °C.
- RH about 60–80 %; avoid long periods near saturation.
- Night: keep leaves and fruit dry; avoid cold nights that harm fruit set.
Targets by stage
| Stage | Temperature (day / night) | RH | Notes |
|---|---|---|---|
| After transplanting | 22–25 / 19–21 °C | 70–80 % | Help roots establish; avoid wilting |
| Vegetative and flowering | 21–25 / 18–20 °C | 60–80 % | Cold nights reduce pollen quality and fruit set |
| Fruit set and fruiting | 21–25 / 18–20 °C | 60–75 % | Avoid humid nights for Botrytis; steady conditions for fruit quality |
| Harvest period | Similar | 60–75 % | Dense canopy: maximise air movement |
These are typical greenhouse pepper ranges; follow cultivar and crop-advisor guidance. See the VPD chart.
Humidity-related problems in peppers
| Problem | Humidity link | What helps |
|---|---|---|
| Botrytis (gray mold) on stems, flowers, fruit | Wet tissue at night, pruning wounds | Dry canopy at night; prune in the morning; remove debris |
| Pepper powdery mildew (Leveillula) | Can develop at moderate humidity on dry leaves; spreads inside the canopy | Scouting, resistant cultivars, control programme; humidity control alone does not stop it |
| Blossom-end rot | Calcium shortage in fruit; linked to uneven water supply and very high or very low transpiration | Even irrigation; moderate VPD |
| Fruit cracking and russeting | High humidity with wet roots; condensation on fruit | Avoid humid nights; steady temperatures |
| Poor fruit set, misshapen fruit | Cold nights; poor pollen | Keep nights warm; moderate humidity at flowering |
See greenhouse humidity and disease and tomato greenhouse humidity for related crops.
Separate three kinds of water
- Root-zone water: what irrigation supplies; measure substrate moisture and drainage.
- Water vapour in the air: RH, VPD, dew point at canopy level.
- Free water on plants and surfaces: condensation, guttation, drips; check leaves and fruit at dawn.
A humidity problem in the air is solved with venting, heating and dehumidification; a free-water problem also needs irrigation timing and condensation control; a root-zone problem needs irrigation changes.
Night control for peppers
- Keep night temperature in the crop's range; heating also keeps leaves above the dew point.
- Start moisture removal before sunset; stop irrigation in the late afternoon.
- Keep horizontal airflow fans running through the night.
- Heat-and-vent at dusk and dawn when outside air is drier; dehumidify when it is not or when screens are closed.
See greenhouse night-time humidity and our greenhouse dehumidifiers.
Equipment brief for a pepper house
- Area, height, spans, screens and heating system
- Planting density and stage
- Night temperature and RH now, and target
- Irrigation schedule
- Power supply and drain points
FAQ
Frequently asked questions
What humidity do greenhouse peppers need?
About 60–80 % RH during active growth, avoiding long periods near saturation at night.
What temperature is best for greenhouse peppers?
About 21–25 °C by day and 18–20 °C at night.
Does high humidity cause blossom-end rot in peppers?
It can contribute by reducing transpiration and calcium transport; very dry, hot air and uneven watering also contribute.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
- UMass Extension, Reducing humidity in the greenhouse.
