Hardening Plants

It’s the time of year when many of us begin to think about moving plants outside that are now growing indoors under a light. It’s a common mistake for beginning gardeners to move their plants outside without first hardening them, but it’s a mistake you only make once! Moving plants outside without hardening them will usually kill them, wasting all the effort that went into growing them in the first place.

There are different hardening techniques, but they are all based on the same principle, slowly introducing your plants to the outdoors after being in your heated home under a grow light. Some people use a cold frame or greenhouse for this. It always takes about the same amount of time, roughly a week.

Whatever method you decide on in the end, here is a good place to start. Begin by setting your plants outside for 15 minutes the first day, then doubling the time each day (30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 16 hours). This is a very uncertain time for your plants, so watch them closely. If they start to wilt or look like they may be dying, stop the hardening process and return them indoors for a few days before trying again. At the beginning of the hardening process place the plants outdoors in the shade, and gradually introduce them to full sun over the course of the week.

4 Replies to “Hardening Plants”

  1. I have lots of plants in my polytunnel. The temperature at night is really not much better than outside it….it has been down to freezing a couple of times. Would I still need to harden stuff for a week, given that they have already survived those low temperatures?
    Thanks for your attention!

  2. It’s not just the temperature, but it’s the exposure to fresh air, wind, direct sunlight and so on. I would say yes you probably will need to harden them, but I’m not completely sure. Depending on how your polytunnel is constructed, you may be able to harden them partly or completely by just opening a flap to let outside air in.

    If you have a plant or two that you could afford to lose if something went wrong, you could let them sit outside for an hour or two. Watch the plants over the next 24 hours, and if they are wilted or show other signs of stress, it’s a pretty good indication you need to go through the whole hardening procedure. If it were me, I would harden them just to be sure.

    My garden is too windy for a polytunnel, so I’ve never used one.

  3. Thanks….I’ll try that.
    We live at the highest point for some distance here so catch a lot of wind, but we do have fences all round which offer some protection.

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