May is the month when warm days begin to beckon tender plants onto the terrace, but beware the cooler night temperatures, which will turn them purple at the edges. The process of hardening-off involves gradually accustoming plants to the rigours of outdoor life, and should not be rushed, but taken in orderly stages. Move plants from the greenhouse to the frame: prop the frame light open during the day, then shut it at night; leave the lights up; then, plant out at the end of the month. All of us needed to learn to walk before we could run.

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