How do I 'harden off' my seedlings, and why?
Although our climate has cold winters, we often grow plants which come from warmer climates. Like tomatoes, for instance. These not only can't stand frost, but get very sulky if subjected to temperatures below 5degC. Yet in summer we can grow them outside!
So what we do is, start the young plants off in very warm, sheltered conditions. These conditions are even more luxurious than the English summer (!). If we were to take plants which have been in a lovely heated draft-proof propagator and expose them to conditions outdoors, they might well die of shock. Even if they survive, the trauma will send them into a self-protective mode which gardeners call 'suffering a check'. When this happens the plant stops growing and it can be hard to get it started again.
At each stage when we move a plant from a more protected environment into a tougher one, we need to get it used to the new conditions gradually. This even applies to plants which, once acclimatised, will stand up to storm and snow. During the 'hardening off' process, the plant develops tougher tissues and sturdier stems.
If you are growing plants in a heated propagator, the initial hardening process goes like this:
Keep a very close eye on the weather forecast, checking for when nighttime temperatures are above 5 deg C. Once they are, you can leave the plants out overnight in your garden or a sheltered area of your allotment. After a few days outside in sheltered surroundings, they can be planted out in the allotment.
ALWAYS REMEMBER TO PROTECT YOUNG PLANTS FROM SLUGS AND SNAILS.
They will be especially vulnerable when they are delicate and tender.
- Open the vents at the top of the propagator. 2-3 days later,
- Take the lid off the propagator. Another 2-3 days later
- Turn the propagator off. Next,
- Move the plants to a frost-free greenhouse or conservatory, which needs to be
- at least 5 deg C even at night. A few days after that
- Move the plants outside IN THE DAYTIME when the weather is nice.
Keep a very close eye on the weather forecast, checking for when nighttime temperatures are above 5 deg C. Once they are, you can leave the plants out overnight in your garden or a sheltered area of your allotment. After a few days outside in sheltered surroundings, they can be planted out in the allotment.
ALWAYS REMEMBER TO PROTECT YOUNG PLANTS FROM SLUGS AND SNAILS.
They will be especially vulnerable when they are delicate and tender.
Hardy plants - those which, once mature, will stand frost and storm - can go through the process quicker. But even they will be vulnerable to spring frosts when they are young. Although you do not need to keep them above 5 deg C, you will need to harden them off somewhere where late 'ground frosts' won't harm them. 'Ground frosts' occur till late in spring on clear nights when the moisture evaporating off the ground chills the air just above soil level.
Ground frosts can be avoided by putting plants higher up on a bench, or by giving them a light covering - say sheets of newspaper or an old net curtain. Speciala 'frost-protection fleece' is also sold for just this purpose.
For more about frost and how it affects the gardener, click here to go to All About Frost
Ground frosts can be avoided by putting plants higher up on a bench, or by giving them a light covering - say sheets of newspaper or an old net curtain. Speciala 'frost-protection fleece' is also sold for just this purpose.
For more about frost and how it affects the gardener, click here to go to All About Frost
