Adjusting plants that are raised indoors or in a greenhouse to outdoor conditions. This is usually achieved by gradual exposure to outdoor conditions.

Toughen plants from the greenhouse by giving lengthening periods of exposure to outside conditions

( see how) The gradual acclimatisation of seedlings grown indoors or in greenhouses to outside conditions, before transplanting. This is often done in a cold frame which is gradually opened more and more each day to let in more 'cold' air.