Hardening off plants in the grow box


When you have seedlings growing indoors or a greenhouse during their life they have had the opportunity spending it in a near perfect environment with controlled temperatures, consistent lighting, no wind, etc.  If you take this happy plant and move it directly into the wild (your garden) it can, and probably will, go into shock leading to its sudden death.  The solution to this problem is to hardening off the plant.  This is a process of slowly getting the plant accustomed to the real world environment a couple hours at a time.

You start by bringing the plant outside for two hours in the late evening or early morning hours.  If the plant begins to wilt let it recover indoors until it appears healthy again.  Each day increasing the amount of time it is exposed to the outdoors over 1-2 weeks period, or until the plant can survive a full day/night outside.  At this time it is ready to get its permanent home in your garden.

This process takes a lot of patience, which as they say is a virtue.  Unfortunately I believe I am missing this virtue.  My history of hardening off plants follows a similar pattern; bring out a plant in the evening with the full intentions of bringing it back in after a few hours, unfortunately I forget and it spends its first day out in the cold all night which normally the demise of my summer plants.


This year I am using my grow box to harden off my plants.  Normally the grow box runs at about 68-72 degrees which is a great environment for my seedlings.  By allowing some hot air to vent and lowering the maximum temperature setting in the software I am able to bump the temperature down to a range of 57-65 degrees.  After a few days I will drop the temperature a few degrees until it has similar low temperature to the outdoors, while still staying at a safe temperature for the plants.

Given today using an unknown neighbor’s weather station we had a high of 48.2F and low of 35.1F I still have some time before I can safely bring my tomatoes/cucumbers outside but they should be toughened (hardening) up and ready to go when it is.

3 Responses to “Hardening off plants in the grow box”

  1. Daphne Says:

    I forget my plants sometimes too. Luckily my subconscious seems to know when I can do this. I don’t do it when the temperature gets too low. They still might have some issues with sunburn, so plant them when overcast weather is predicted. Do you have a fan in your grow box that you can use to toughen up the stems?

  2. Robert Says:

    It’s not just temperature that you need to harden the seedlings against. The sun is much stronger and a different quality of light compared to your grow box. You will still need to gradually move them outdoors or they could get scorched.

  3. The Cheap Vegetable Gardener Says:

    Daphne, yes I have a fan blowing hot air down so should be pretty tough stems.Robert, I live in the Pacific Northwest, we don’t see the sun until end of June 🙂 If for some strange reason the weather gets nice I will plan on giving them a little artifical shadeI am also reducing the daylight hours to match the conditions outside, which also saves on power.

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