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How To Harden Off Seedlings

Raising seedlings can be somewhat of a daunting process, especially if you have never done so before. Here you will learn the meaning of the term to harden off, why, how, and when to use it. Gardening is a process of trial and error, but if you can give your seedlings the best chance to succeed, you will overcome many beginner mistakes and the first one is not adequately hardening off your indoor raised seedlings.

What is hardening off?

Hardening off is the process of moving your indoor started seedlings from their cosy, comfortable and regulated environment into the outdoors. Moving your seedlings can be a delicate and slightly time-consuming effort, but it’s worth the wait knowing you’ve done you’re very best to make sure they’ll succeed for the season.

How do I start hardening off?

A greenhouse or cold frame is a great tool for hardening off as this will allow your seedlings exposure to the shift in temperature but not necessarily wind or rain which can be too harsh. To start, place your seedlings in their new environment for a few hours on the first day, two should be enough, and then return them to where they were raised. On the next, leave them out for a few more hours and on the following, a few more again. Once you’re at the week mark and they’ve been outdoors for the duration of the day, they should be ready to stay out overnight, so long as no danger of frost is present. Dwellings such as greenhouses and cold frames have the advantage of windows or doors that can be opened increasingly with time to gradually bring the outside in, ready for when there is no structure at all.

What if I don’t have a greenhouse?

You don’t require an outdoor structure to successfully harden off your seedlings but you may have to be a little more diligent if the weather takes a turn. Begin by introducing your plants to the outdoors on a grey or overcast day with little to no wind. If a light breeze is a present try placing your seedlings in a tub or box so they are protected from the wind, not only will it dry them out but it can damage the growth if too strong. Avoid setting them in the direct sun, this can lead to scalding on foliage and will ultimately affect the health of the plant. The process is the same as above, leave them out for two hours on the first day and then return them inside. On the next, a few more hours and a little bit of morning sun, then the following, a few more hours and more sun again. Between 1 – 2 weeks your seedlings will be ready to sow.

Extra tips to note:
  • Avoid direct sun, frost, strong breezes, or wind.
  • Water the seedlings before setting them out as the new environment may dry them out.
  • Grow an extra seedling or two as a backup and keep them safe indoors.
  • Place shade cloth over the seedlings if the sun is too direct and hot.
  • Avoid placing them on the ground where they can be knocked over or slugs can access.
  • Bought seedlings may also require hardening if grown in a sheltered environment.
  • Don’t rush the process! Patience is key.

How do you harden off your seedlings? Leave your personal tips and tricks in the comment section below.

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