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What is Hardening Off?

Seeds and plants raised on the windowsill or in the greenhouse need to be ‘hardened off’ before planting into their final growing positions in the garden.

Hardening off is the process of putting plants outside during the day but returning them indoors for the night. This helps the plants acclimatise to the cooler outdoor temperatures and lower humidity.

HOW LONG TO HARDEN OFF PLANTS?

For a period of two weeks. If your plants are in the coldframe you can easily open or remove the transparent lid during the day and replace it during the evening. This is much quicker than having to take individual pots in-and-out all the time.

Week 1
Place outside during the day and cover with two layers horticultural fleece, return indoors early evening.

Week 2
Place outside during the day and cover with one layer of horticultural fleece, return indoors early evening.

Week 3
Leave outside with no fleece covering.

Week 4
Plant in their final growing position.

EFFECTS OF NOT HARDENING OFF PLANTS

How would you like to be taken from a warm bath and thrown out of your front door on a freezing cold night? Not nice and that’s exactly how the plants would feel. The shock would either kill them or would ‘check’ their growth. ‘Check’ is the gardening term for stunting growth, slowing down their natural rate of growth.

EFFECTS OF HARDENING OFF

Stems become thicker and develops a sturdy plant that can withstand the great outdoors much better than being directly planted from the greenhouse.

WHEN TO HARDEN OFF PLANTS?

Late Spring is the time to start hardening off your plants; after your last local frost date. Talk to other local gardeners to discover when this is.

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