# Microclimate

> A microclimate is a small zone within the grow space whose temperature, humidity or airflow differs from the room average, such as inside a dense cola or a corner.

- Canonical: https://genetixbay.com/knowledge/glossary/microclimate.html
- Also written: micro-climate, micro climate, canopy microclimate, hot spots, dead air pockets
- Glossary category: Environment and light · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A microclimate is the local environment in one small part of the grow space, which can be very different from what the room sensor reports. Common examples: the humid, still air inside a dense canopy, a hot spot directly under the centre of a fixture, a cold corner near an intake, or the air right next to the medium surface.

## In practice

A sensor at mid-height in an open spot might read 24 °C (75 °F) and 50% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), while the air inside a thick [cola](https://genetixbay.com/knowledge/glossary/cola.md) near the bottom of the canopy sits several percent higher in RH with almost no air movement. That is where [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) start. Dense, unpruned lower canopies are the classic problem.

How to manage microclimates: move the sensor to canopy height and check several locations; run [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) above and below the canopy; thin lower larf that will never ripen; space plants so air can pass between them. Check the coldest surfaces after lights-off for condensation.

## Don't confuse with

- **Boundary layer**: the still air film directly on a leaf surface, millimetres thick.
- **Room average**: what the controller sees; microclimates are why it can mislead.

## Related terms

[Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md)

## Read more

- [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md)
- [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)

## Sources

1. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182.
2. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142