Quick answer: Commercial orchids, mostly Phalaenopsis, like warm, fairly humid air: typically 60–80 % RH, with warm temperatures (around 26–29 °C) during vegetative growth and a cooler period (around 18–20 °C) to induce flower spikes. The danger isn't high humidity itself. It's free water: water left in the crown or leaf axils at night favours bacterial soft rot and crown rot, and condensation on flowers causes Botrytis petal spotting. Control means drying the crown and flowers before night, avoiding condensation when temperatures drop, and removing moisture when ventilation would cool the house too much. Follow your cultivar and propagator guidance for exact setpoints.
Quick answer (typical Phalaenopsis ranges)
- Vegetative: warm, about 26–29 °C, 60–80 % RH.
- Spike induction: cooler, about 18–20 °C, for several weeks.
- Keep crowns and flowers dry at night; avoid condensation.
Typical conditions by stage (Phalaenopsis)
| Stage | Temperature | RH | Humidity focus |
|---|---|---|---|
| Young plants, vegetative | About 26–29 °C | 65–80 % | Steady growth; water dries from crowns before night |
| Spike induction (cool phase) | About 18–20 °C | 60–75 % | Cooler air reaches dew point more easily: watch condensation |
| Spike development, flowering | About 20–23 °C | 55–70 % | Dry flowers to avoid Botrytis spotting |
| Finishing, shipping prep | Per buyer spec | 55–65 % | Clean, dry flowers |
These are typical commercial ranges; cultivar and propagator guidance sets the actual targets. Other genera (Cymbidium, Dendrobium, Oncidium) have different temperature needs.
Where humidity problems come from in orchid houses
| Problem | Water involved | What helps |
|---|---|---|
| Bacterial soft rot, crown rot | Water in the crown and leaf axils, especially at night | Water early in the day; airflow; dry the crown before night |
| Botrytis petal spotting | Condensation or high humidity on open flowers | Avoid condensation; dehumidify at night in flowering zones |
| Root rot | Wet substrate, poor drainage | Irrigation and substrate management |
| Slow drying after irrigation | Humid, still air | Horizontal airflow; moisture removal |
See Botrytis and greenhouse humidity, which also covers leaf wetness duration.
Separate air, substrate and surface water
- Air humidity: RH, VPD, dew point at plant level.
- Substrate moisture: bark or moss drying time; irrigation.
- Surface water: crowns, leaf axils, flowers, benches, drips from the roof.
A house can read 70 % RH and still have water standing in the crowns. Check at dusk.
Night control
- Water early so crowns dry before sunset.
- Keep air moving through the benches at night.
- During the cool induction phase, keep the dew point below leaf and flower temperature; see night-time dew-point control.
- Vent or heat-and-vent when outdoor air is drier and the heat cost is acceptable. Otherwise dehumidify; see ventilation vs dehumidification.
Our greenhouse dehumidifiers include ceiling-mounted and ducted units for bench houses.
Information for an equipment review
- House area, height, benches, screens
- Genus, cultivars, stages by zone
- Irrigation method and times
- Night temperature and RH now and targets
- Where water is found (crowns, flowers, benches)
- Power and drainage
FAQ
Frequently asked questions
What humidity do orchids need in a greenhouse?
Commercial Phalaenopsis are typically grown at about 60–80 % RH, with drier air around flowering.
Can orchids have too much humidity?
High humidity with free water on crowns or flowers at night causes rot and Botrytis spotting; the issue is wet surfaces.
What temperature makes Phalaenopsis flower?
A cooler period of about 18–20 °C for several weeks typically induces spikes; follow cultivar guidance.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
- University extension guidance on greenhouse humidity and Botrytis management.
