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How To Harden Off Your Plants

Hardening off plants is much easier with a cloche (cold frame) - click here for more details of cold frames. 

Using a Cloche To Harden Off
Place the cold frame facing south or south west to receive maximum sunlight, against a fence or wall to provide protection from wind. It is a good idea to examine the garden on a frosty morning to see which areas are relatively free from frost - this will help you decide where to place the cloche.

The hardening off process should take about two weeks before planting outside. For tender plants (like tomatoes, runner beans, sweetcorn, geraniums, salvias, buzzy lizzies, begonias and petunias) start the process around the last frost date. Some plants can withstand a degree or two of frost (alyssum and antirrihnums), these can be hardened off a month before the last frost date and planted out a week or so before the last frost date.

For the first week, ventilate the cloche only on warm days, and always close the cloche in the evening and night. During the second week, gradually increase the ventilation period, leaving it off in the evening where no frost is threatened. 

No Cloche Available?
Examine the garden on a frosty morning to see which areas are relatively free from frost - choose these areas for your plants. Any protective barrier you can provide against the wind chilling the plants will greatly help. During the first week, place the plants outside during the warmest part of the day (a few hours at first) bringing them back indoors / under cover after this time. 

During the second week, leave them outside for the day, bringing them back in during the evening.

Covering the plants with horticultural fleece during this process will greatly increase your success rate and is very cheap protection (see cloche article for details).