Hardening off your plants
It’s important to gradually acclimatise tender bedding and vegetable plants grown under glass to outdoor conditions. This process should take about two weeks, depending on how much warmth they’ve been used to, how tender they are, and your local climate. The difference between the last frost in the north and south of the UK can be as much as a month. The third week of May is normally quite safe in the south, while in the north it’s well into June. So keep a close eye on your local weather forecast.
It’s the leafiest tender plants that are most vulnerable to damage from frost, wind or bright sun, so take the greatest care with these. Hanging baskets and mixed planters need to be hardened off too, unless the plants were acclimatised before potting up. When buying plants, ask whether they’ve been hardened off already.
Plants dry out faster in moving air, so check them regularly when outside, as they may need more water.