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.
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.
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.
the second week, leave them outside for the day, bringing them back in
during the evening.
the plants with horticultural fleece during this process will greatly
increase your success rate and is very cheap protection (see cloche
article for details).