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harden off

British  

verb

  1. (adverb) to accustom (a cultivated plant) or (of such a plant) to become accustomed to outdoor conditions by repeated exposure

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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Remember to harden off, or acclimate, homegrown starts by giving them a few midday hours of sunbathing for about five days before planting them outside.

From Seattle Times Apr. 28, 2022

If possible, move the potted seedlings into a cold frame to harden off for a few days before planting.

From Seattle Times May 19, 2016

You can leave the tubers in the ground for a couple of weeks to harden off a bit, and then lift them carefully with a garden fork.

From Washington Post

Sow the seed early in spring in a slight heat, harden off gradually, and put out at the end of May in a warm, sheltered spot.

From Gardening for the Million by Pink, Alfred

Take up to the light any time after first of March in the spring, but be careful to harden off before setting outside.

From Gardening Indoors and Under Glass A Practical Guide to the Planting, Care and Propagation of House Plants, and to the Construction and Management of Hotbed, Coldframe and Small Greenhouse by Rockwell, F. F. (Frederick Frye)

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