Bringing Plants Outside – How to Harden off Plants

by | Apr 25, 2018 | Guides, HowTo's, Tips & Tricks | 14 comments

Growing your plants indoors from seed is a very controlled and nourishing environment. The outdoors is a drastic change from what your tender seedlings and young plants are used to. Before bringing them outside it is important to know how to harden off plants so they do not die or suffer from shock.

Hardening off plants is a gradual introduction to the new elements of the outside. This includes the variations in temperature, winds, and the UV light of the sun.

Tragic Tales of Plant Loss

I have experienced it for myself and heard it many times from others. Beautiful healthy seedlings and young plants that transplanted into the garden only to wilt, break or die. It is a tragic tale that is avoidable by proper acclimation. Hardening off your plants takes a bit of effort but is 100% worth it.

This can also happen when you bring plants home from a nursery or a box store garden center. Often these plants have not had a hardening off period to the outdoor elements.

It is always better to err on the side of safety. Harden off plants you buy unless you are specifically told they have been acclimated.

Common signs of improperly hardened plants:

Sun Scald:

Whitening of leaves or large white spots. The result is sunburn. Yes, your plants can get sunburn like us. Especially if they have not been exposed to the strength of the UV rays that true full sunlight emits. Windows, greenhouse glass, and grow lights do not emit the UV rays like the sun. This sudden introduction of UV can cause the outer layer of the plant tissue to burn up leaving white spots. This can harm the plant’s ability to perform photosynthesis. Severe damage will result in death.

Discolored drooping leaves:

Although this can include other issues, often this indicates a weather shock. A cold weather shock can mimic a frost reaction in young plants that have never been exposed to temperature extremes. Their young leaves can wilt and brown due to the sudden change in ambient air temperature.

Snapped and Damaged stems:

Young seedlings that have not been exposed to any air can be easily be damaged by even mild winds. You can help prepare them in advance by running a low fan on them indoors as they grow. The constant force will encourage strong stem growth. Hardening off gradually also prepares them further for the force of winds in your area. Offer tall plants additional support when you plant them.

How to Harden Off Plants

Hardening of your plants should take 10 to 14 days. In some cases, you may decide to take a little longer if your weather conditions in the evening may be too cool for immediate transplanting. Try to stick with the schedule of exposure as much as possible.

Prepare in advance

You will need to pick the first area carefully as this will be the most sensitive time for your plants. This will need to be a sheltered shady area that gets minimal to only filtered sunlight throughout the day. A covered porch on the north side of your house that gets little to no direct sunlight. A picnic table that you could put in a location that the underside would remain shaded through most of the day. Or possibly setting up a canopy shelter.

You will also need a box, wagon or larger pots to hold the smaller transplant containers. This will help you to transport plants inside and out, as well as offering them support from being tipped over by the wind.

Always make sure your plants are watered well during the hardening off process. Air temperature and wind will cause greater water loss. Bring them back inside at night.

Day 1 to 3:

Bring your plants out during the day to your shady location. Make sure there is no danger of extreme temperatures or frost. Bring them in before dusk when temps are still warm.

Day 4:

Bring your plants into exposure to some morning or early sunlight for about an hour, 2 at most. Move back to shade for the remainder of the day. Bring in a little later in the evening but before dark.

Day 5:

Give your plants 2 hours of morning sun, shade and 2 hours of later afternoon sun. If evening temperature is warm enough allow plants to remain until dark before bringing in.

Day 6 – 10:

Increase sunlight by 1 hour each day. Monitor your plants for any signs of stress. Increased sun can cause drying of the soil, watch watering carefully. Try to stretch the length of time they are exposed to the dark evening air as well before bringing them in. By day 8 if the night temp is 50 or above leave them out.

After the 10 days, strong seedlings and plants that show no signs of stress can be safely transplanted into the garden or container.

Day 10 – 14:

Continue to increase sunlight gradually for those tender seedlings that need more adjustment time. They should be strong enough to be left outside now if temps at night are not too low. If the plants are showing too much stress. Reduce them to shade for a few days and nourish with fertilizer. I always recommend worm casting, or worm casting tea. Follow this link for a review regarding worm castings’.

Work schedules can hinder the ability to move plants through-out the day. You can choose locations or a location in your yard that mimics the lighting conditions of partial sun and shade if needed.

 

Tips & Tricks for Acclimating Your Plants

√ Acclimating or acclimation is the hardening process. It is the adjustment made by a plant or organism to a change in environment or condition. You can learn more about the details of Acclimatization by following this link to Wikipedia.

√ In colder growing zones cool nights can impact warm weather plants like tomatoes, peppers, and eggplants. Consider cloche or a cold frame as a part of your hardening off process or even in your garden to better help them harden off.

√ Don’t Rush the process. I know you’re anxious to get your plants in the garden. Hardening off can also seem tedious at times. It is worth it though. Stronger healthier plants! That means fewer issues all growing season. Your garden is worth it!

√ Nourish your babies before and after acclimating. Fertilizing is likely something you have already been doing indoors as your seedlings have been growing. Before hardening off and during transplant give them an extra nourishing boost with natural fertilizers that do not harm. Remember chemicals can burn when used in excess. Even some animal manures can cause fertilizer burn. I highly recommend worm castings’ sprinkled or make a castings’ tea. This natural nourishment will give them a healthy boost as they transition.

A Video Example

This video reviews a lot of what is already said here but offers a nice visual guide. The result is also one of my favorite YouTubers for gardening. Praxxus55712. Give him a subscribe if you enjoy the video.

Nourish Your Seedlings, Transplants & Garden With A Natural Fertilizer they can use Immediately & Safely

Worm castings are a safe natural option to provide your plants with the nutrition they need at all stages of development. They do not burn, harm your soil or take time to be used. Your plants can use the power of worm castings right away. Making them the best way to feed your growing garden.

The Benefit of Hardening-off Your Plants

When learning how to harden off plants you are ensuring the next best healthy step for your plants. They will thank you with less stall in growth when transplanting and stronger growth through the season. This, in turn, leads to greater yields in the future.

I have mentioned it in previous articles as well. Healthy plants are more pest and insect resilient. They have a better chance of fighting mold, fungus, and bacterial illness. Healthy plants can recover better from extremes in weather.

A bonus from healthy plants is a future generation of strong plants. You are enabling strong seed production for better future generations and offsprings of your garden as well.

Growing a garden is a lot like raising children. The more you prepare them for the different stages of their life, the better parents they will red arrow down rightlater become in the future.

Drop your comments below and let me know how things are going in your garden and with plant acclimation.

Happy Growing Friends!

14 Comments

  1. Sharon

    In my early days’ experience of growing and transplanting, many of the seedlings died. It would be great if I got to read this article then. Anyway, I am sure those who are interested will benefit well from here. I mostly grow herbs by propagating and the process of acclimation is the same. Great tips sharing! Will be coming back here for more.

    Reply
    • Christina

      Hi Sharon,
      I am with you. When I first started gardening I made those mistakes too. Was so excited just to go out and plant that I never even thought about it. Hardening off a plant was a concept and idea that was foreign to me. I turned to grandma then (who was my gardening guru) and asked what I did wrong. I was sure I had bad soil or something. I had missed that important step!
      I do a lot of my herbs through propagation as well. I also collect some seed from others. I love to continue the line of healthy stock growth in my plants. Lineage in plants can be amazing.
      Happy Growing!
      Christina

      Reply
  2. Tracy Fryer

    It’s always a toss-up between starting early in the greenhouse with hardening off and starting in a seedbed outdoors where they are going to grow anyway. I live in Scotland so the growing season is not as long or warm as further south. What do you think?

    Reply
    • Christina

      Hi Tracy,
      I think it really depends on what you intend to grow. Due to your short growing season you could add some longer to harvest plants by starting them early indoors, or greenhouse and transplanting. Those that have a short growth cycle I would direct seed whenever possible.
      I am fortunate in NC, US grow zone 7a to have a pretty extended growing season. It does have an extended period of cool in spring and fall great for cool weather plants and a fairly long hot summer for warm lovers. Many cool weather crops, like greens, cool herbs like borage, cilantro, and dill I will direct seed in the garden or in a container. Although some lettuce, kale and other greens I will start inside so I stagger harvest times.
      My warmer weather plants like Basil, tomato, and etc. I will start indoors or in a greenhouse.
      I also have a varied amount of plantings that I do throughout the year that I shuffle in and out. These perennial types can’t tolerate my cold winters. I have to harden them off each year to re-adjust them to the elements. Those include my hibiscus, ginger, flowering ginger, turmeric, rosemary and some others.
      So it really is all dependant on what you want to grow and your harvest schedule. Because of your shorter season, you could add some simple extensions with cloches and/or a cold frame. This would give you a jump start or an extension on some of your plant choice.
      Most plants will transplant well with the right nourishment and care so you can experiment a bit and see what offers you the best growth and production. If you are going to seed start any cautionary plants that have sensitive tap roots I would suggest using recyclable peat style pots that plant directly in soil or a bio sponge type material that does not disturb roots. I reviewed a product recently that helps with potential transplant shock. Easy Seed Starting: Use Rapid Rooter Plugs.
      Please let me know how it goes!
      Christina

      Reply
      • Tracy

        Thank you, Christina, for the tips. I think I will try the peat pots this year. Straggly roots when I transplant bother me (and the plant!).

        Reply
        • Christina

          Your very welcome 🙂 Here any time you want a tip, question or if you would like to share your success!
          Happy Growing!
          Christina

          Reply
  3. Cathy

    Hi, Christina!

    I really enjoyed reading this article and also watching the video! Years ago, I owned a florist and recall how we followed the very steps you’ve mentioned in this article. Yes, it is a bit of work but so worth it in the end!

    You have provided very important tips to follow for anyone who needs their plants to acclimate from the indoors to outdoors. I like the way you’ve outlined what needs to be done from day 1 through day 14. Do you have your own greenhouse?

    Excellent article!

    Thank you.

    Cathy

    Reply
    • Christina

      Hi Cathy,
      Having a florist shop must have been wonderful. I love visiting florist, nurseries, and greenhouses.
      I have had small greenhouses. We purchased a new home with more land this past fall. The plan is to add a larger greenhouse now that we have the space for additional growing. The smaller one I will be using strictly for hydroponics. It is part of the dream of mine to do a lot more greenhouse growing. I am lucky enough to have a lot of growing space indoors as well. Although my husband and family may say it looks like a jungle in here sometimes lol.
      I appreciate your feedback on my hardening off methods. I hope that it will save people the tragedy of having plant loss. I know I experienced it early on when I overlooked these important steps.
      I look forward to communicating with you more and learning about the wonderful plants and flowers you enjoy growing.
      Christina

      Reply
  4. Jeff

    I am truly impressed with your website, I love how easy it is to find everything plus your post answer so many of my questions. I have been gardening for a very long time since a boy actually, but I have little experience and luck with growing plants indoors. I don’t know when I am watering my indoor plants enough or too much, I was just curious if there was any secrets you could share with me on this topic. I also wish to grow herbs in my kitchen, but I am not sure they will do well since I live in a climate with very cold winters?

    Any help much appreciated,

    Will you be having a newsletter in the future

    Reply
    • Christina

      Hi Jeff,
      Thank you so much. I appreciate your compliments.
      Watering is actually the leading cause of plant failure. I recently wrote about it in an article. You are not alone in facing issues and questions when it comes to watering indoors. I have made plenty of mistakes myself. You can view the article here. Indoor Gardening Tips for Watering Plants I think this should help with any question. If not, just let me know and I can try to help.
      I grew up in upstate NY near Buffalo. Those are cold winters with lots of snow. Indoor gardening and growing herbs were something on a farm I grew up familiar with. It was a bit tougher than with only the use of windows and not grow light options like today. My grandparents made it work. hanging plants and window sills full of plants was a common site.
      Herbs are a great inside choice anytime of year and especially in winter. They are mostly greens so 6 hours of light a day that is winter average in a sunny window is usually enough. (more can be great) The even temps indoors will help most of them be very content! Watch for drafts for some warm lovers like basil in the winter. If you are lacking light there are many easy and budget-friendly grow light options today that work well for small indoor spaces. Best LED grow lights I reviewed some on this link that fit well indoors.
      Also many herbs like low light and even tolerate some shade. Herbs that grow in shade – low light herbs They make great options!
      Start small with some herbs that you will use. This will help get your feet wet with indoor growing 🙂 Since you garden outdoors, you can easily get some cuttings rotting in water to get a jump start. Basil, mint family and many others root fast in water.
      A newsletter is a nice idea. I had not thought about it. I was considering doing some ebooks in the future for my subscribers. Perhaps I will get to both. Thank you for the suggestion.
      Happy Growing Friend!
      Christina

      Reply
  5. Pernilla

    Hello Christina!

    Since some years my husband and I are living in a house. We have a garden and we love to create colourful flower borders and grow vegetables, like tomatoes, squash, potatoes, paprika and more. My husband loves to experiment and in the springtime, we have uncountable pots of seedlings in our house. The first year we did witness the ”Tragic Tale of Plant Loss”. The second year we were more careful and most of the small plants survived.

    We still have a lot of things to learn. Your ”hardening off method” is great. I’ll follow your guide this year and I believe our plants will be rejoicing this and reward us with even stronger colours and a bigger harvest.

    Grateful for your wonderful tips.

    Pernilla

    Reply
    • Christina

      Hi Pernilla,
      I am glad that you found the hardening off methods useful. Once you develop the habit it will become second nature and yes your plants will reward you 🙂
      Paprika peppers are something I am just starting this year for the first time. I grow many other types of peppers. I am excited to harvest my own paprika. I wonder why I had never grown it in the past. I may need to reach out to you at harvest time and get some of your preserving tips. I know I would like to do some smoked paprika. It is one of my favorite spices to use. There is so much that can be learned and shared. I grow and have grown a lot of herbs, but by far not all 🙂
      Happy Growing. Please keep us updated!
      Christina

      Reply
  6. Pernilla

    Hello Christina,

    Paprika is just wonderful. You can do so many different sorts of dishes. The ones which gets too much to eat we preserve them by pickling them, freezing them after having blanched them or cutting them into small pieces and let them dry for use in sauces and dressings.

    Have fun with your baby peppers and enjoy the harvest in the autumn!

    Pernilla

    Reply
    • Christina

      Hi Pernilla,
      Thank you. I am looking forward to enjoying these. They seem to be doing very well right now with lots of lovely blossoms. Think they will produce very well.
      Thank you for the tips!
      Christina

      Reply

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