# Hardening off

> Hardening off is gradually exposing plants raised indoors or under a dome to harsher conditions, such as sun, wind and lower humidity, so they adapt without shock.

- Canonical: https://genetixbay.com/knowledge/glossary/hardening-off.html
- Also written: harden off, hardening, acclimatising, acclimatizing, acclimation
- Glossary category: Cultivation and training · 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"

Hardening off is the gradual acclimatisation of a plant to a tougher environment. Indoor-raised plants have thinner cuticles and leaves adapted to low light and still air; put straight into full sun and wind they can bleach, wilt or stall. Over one to two weeks they thicken their leaves and cuticles and adjust [stomata](https://genetixbay.com/knowledge/glossary/stomata.md).

## In practice

For outdoor planting, start with an hour or two of morning sun or shade outdoors, increase daily, and bring plants in on [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) until they spend full days and nights outside. Night temperatures should be reliably above about 10 °C (50 °F) before planting out. For clones coming out of a dome, the same idea applies to humidity: vents opened over several days.

Note that full sun can exceed 1,500-2,000 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) PPFD at midday, several times what most indoor plants have seen.

## Don't confuse with

- **Transplant shock**: damage from root disturbance; hardening off addresses the above-ground environment.
- **Stress training**: deliberate bending or damage to shape plants, unrelated.

## Related terms

[Cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md), [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md), [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md)

## Read more

- [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md)