Strength Training for Your Plants

How to Harden Transplants

If you have a sun room, green house, or a really large south facing window area - I am jealous. Jealous because starting seeds in real sunlight is so much easier than starting them under artificial sunlight. By easier, I mean the transition from indoors to out in the garden.

Plants that are started and grown for the first weeks of their life indoors are fragile and not ready for the real world. If you were to take your plants from inside and plant them in the garden all in one day, it would be like taking someone who has been cooped up indoors all winter and dropping them out on a beach under the sun by the equator without sunscreen.


For those of us that need to start plants indoors, there is a very important step that can make our break the success of their growth and survival. This is the act of hardening off your plants. To harden your plants is to strength train them. To dip them slowly into the harsh elements of the real world. And it can be challenging because the weather outside does not like to cooperate. Let me explain how I go about hardening off my spring plants.

Pick Date

First, pick a week slightly prior to the date you would like to plant your vegetables outside. Make sure it is not too early. For me, I like to start hardening off my spring plants the week of April 15th (this may be different in your zone). The reason I chose this week is because the weather where I live starts to make a transition towards warmth. There are still some cold days, but these spring plants are cold tolerant plants.They can handle a frost or two and generally taste better when it’s cold out. If you take a look at the last six years in my region from April 8th through April 22nd, the days (max temperature) generally do not get below freezing. Only two days have been slightly above.

And if you look at the same date range for the minimum temperatures (night time) there is a noticeable shift historically. There will still be days that go into freezing. But this is ok during the hardening off phase as you are bringing your plants inside at night.

Looking out a little over a week when the plants will be ready for the garden, the minimums have historically been much improved and suitable for these spring plants. Any sooner than this and you put your plants in some risky conditions.

Nightly Lows

Of course, I say all this now, but looking ahead at the weather this year and it seems like it may stay cold and not follow this train of thought at all. You must play these things by ear sometimes.


Once your week has been picked, start acclimating your plants by putting them outside under shade. I usually put them in full shade a day or two entirely at least. From there, slowly introduce your plants into morning light an hour at a time - increasing the time each day. Also, be conscious of if it will rain and what the wind might be like. Sunburn is one hazzard, wind burn is another. During this time, do not bring them inside the house if you can help it. At night, it may make sense to bring them into your garage or shed, but they may bring bugs and stuff back into your indoor garden if not careful.

My shade place of choice happens to be behind a hedge bush that faces west. Very easy to bring the plants out into the sun and return them when needed. The hedge and my house offers some protection from the elements.


By the end of 7 days, you should feel pretty good about planting them in the garden with minimal stress. If not done properly, your plants can suffer from transplant shock where they will become stunted and not grow like they should or even die. Like I said, fragile. Try not to plant them on a super hot sunny day, opting for shady weather.


One thing to note is that if you can afford to buy some fleece covers for your plants, these can be a real help in the transition. Supposedly they can raise the temperature of the plants beneath them by 2 to 3 degrees. I will even put these out to protect the plants from pests like rabbits too!

And that is it! You have now successfully transplanted your vegetables started indoors to the great outdoors. It may take a little trial and error to get this right, but it can really give you a jump start on the year. Make sure you understand what plants can go out when. For example, do not plant your tomatoes and peppers outside in April (in Zone 5). They can not handle frost and the weather here is unpredictable.

This is currently what I am doing, how are your plants fairing? Post in the comments below.

Good luck making the transition for this year’s growing season!

About the Author

Geoff has been growing plants and vegetables consistently for the last 6 years and actively experiments with, and writes about, all aspects of gardening.


  1. Looks like a jungle in there!

  2. April Showers and May Vegetables | The Four Season Gardener
    May 14, 2018 - 11:21 am

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