Gardening: Now is the time to harden off your tender plants

hardening off
hardening off

‘Ne’er cast a clout ‘til May is out’ is the old saying (meaning don’t go out without a coat before the end of May).

It’s also the perfect way to sum up treating tender plants.

hardening off

hardening off

Our last frost dates are the end of the month, so if you haven’t started already, now’s the perfect time to start hardening off half-hardy and subtropical plants.

Under glass, even hardy plants get used to regular watering, still air, and stable temperatures.

Putting them outside to survive in widely fluctuating temperatures, much stronger sunlight, and winds will lead to a check in growth, even death if they are caught by frost.

The effect of hardening off is to thicken and alter the plant’s leaf structure and increase leaf waxiness.

hardening off

hardening off

It ensures new growth is sturdy although much slower.

You need to harden off gradually, over a couple of weeks. On a mild day, start with two to three hours of sun in a sheltered location.

Protect seedlings from strong sun, wind, hard rain and cool temperatures. Hardy plants acclimatise faster than tender kinds.

If you don’t have a cold frame, place plants in a sheltered position in front of a south-facing wall or hedge and cover with horticultural fleece to prevent sun scorch and temperature shock.

For the first week, leave outside during the day, but bring in at night. In the second week, leave outside at night, but keep covered (unless there’s a frost forecast).

Towards the end of the fortnight, leave them uncovered before planting out.

Covering with an old curtain or extra fleece can protect from sudden sharp night frosts.

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