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Seed Starting 101: Hardening Off

May 19th, 2010

If you’ve grown your seedling inside under lights they’ll need to be hardening off before planting them in the garden. They’re not used to the harsh real sunlight or the changes in temperature that happen in the spring. Since seedlings are still small plants they’re more affected by these changes, especially if they’ve been living the good life inside your climate controlled seed starting area. Now that the danger of frost is over and the night time temps are regularly above 50 you can start hardening off your tender plants.

Hardening off isn’t that difficult, but it can be time consuming. You want to expose your plants to the outdoor elements gradually. Usually you’ll start with 2-3 hours and work your way up to 10-12 hours. If you have a sheltered location that gets morning sun you can put them in this spot and move them around the garden to locations where they’ll get more and more sun each day. I like to harden off seedlings on my front porch, they get afternoon sun and nice breezes, but they’re protected from getting sun all day long. They also stay warmer at night because of the porch roof. Some people use their cold frames to harden off their plants since it keeps the temperatures warmer overnight. You’ll have to use a shade cloth in combination with your cold frame though if your seedlings haven’t been exposed to a lot of real sunlight.

Personally I’d rather have my seedlings exposed to the natural elements for their entire lives, but the weather doesn’t always permit this (especially here in NE Ohio). If it’s a mild spring I’ll carry all my seedlings out and leave them on the front porch, only bringing them inside when the temperature dips into the 40’s. If I’m lucky I’ll only have to carry them in a few evening a week, if it’s a cold spring I spend a lot of time carrying them in and out of the house or garage. It’s worth the effort though because I believe the little plants do much better when grown in their natural conditions. I’m considering investing in a nice shelf with wheels so I can just wheel them out into the sun and back into the garage at night. But for now I’m happy to carry them in and out, it’s good for the biceps.

Any great tips for hardening off seedlings?

The rest of the Seed Starting 101 Series
Why Start from Seed
Getting Started
Soil Mix
The Needs of Seeds
My Workflow
Diseases and Problems
Hardening Off
Learn More Each Season

Visit my Amazon store to see what seed starting supplies I like.

11 Comments to “Seed Starting 101: Hardening Off”
  1. Lisa Anne of This Urban Homestead on May 19, 2010 at 9:48 am

    I love reading your blog! I am in Cleveland and feel the same about trying to get my little plants out in the environment as much, and as early, as possible. With this Spring, I have been doing a lot of time outside with them, bringing them in only for the thunderstorms or the temperature dips. I am thinking it is almost time to put everything into the ground FINALLY! What do you think?
    .-= Lisa Anne of This Urban Homestead´s last blog ..5 Dollar Dinner: NYT Outtakes: Urban Ag’s Political Roots =-.

    Reply to Lisa Anne of This Urban Homestead's comment

    • Susy on May 19, 2010 at 9:50 am

      Yep, as soon as things dry out here I’m going to be transplanting everything into the garden.

      Reply to Susy's comment

  2. Melissa on May 19, 2010 at 12:34 pm

    Susy, I can see you’ve been busy! My garden is on the verge of being in full swing… I can hardly wait! I just posted pics. I’m collecting new canning recipes this year and you can bet I’ll be ready for those tomatoes! Salsa… spaghetti sauce… stewed tomatoes… Yum! The only things I plan to can this year are tomatoes (can’t even imagine not having them year round!) and preserves/jellies/jams. : ) Melissa
    .-= Melissa´s last blog ..A garden update =-.

    Reply to Melissa's comment

  3. Morgan G on May 19, 2010 at 4:48 pm

    No tips of my own, but I am sure grateful for yours. My tomatillos are reading for this process. Thanks, Susy.
    .-= Morgan G ´s last blog and Hubs’ Kauai Top 10 Day One: The Okolehao Trail =-.

    Reply to Morgan G's comment

  4. heather jane on May 19, 2010 at 11:15 pm

    Hello there! I’m so happy to have recently found your blog. I’ve been starting seeds for two years now, and I’ve had several people request more information about starting seeds. Since I’m rather busy as a teacher here at the end of the year I have not had time. Now I can just send them here. This is perfect.

    I do have one question. I notice your tomatoes are in bigger pots. Do you start them that way or do you transplant them from smaller cells? I use pet pellets and then pop mine into bigger pots when they get a little leggy. Considering I’ve just begun a rather big project of growing a market garden this year, I will be starting even more seeds next year and will use cells. I’m just wondering what you do when things get bigger?


    Reply to heather jane's comment

    • Susy on May 20, 2010 at 9:06 am

      I start them in small cells and transplants to bigger ones. I try to time it so I only have to repot once. This year I started all of them a littler later since I ran out of room and pots last year.

      Reply to Susy's comment

  5. Bruce on May 21, 2010 at 5:02 pm

    Yep, as soon as things dry out here I’m going to be transplanting everything into the garden.

    Reply to Bruce's comment

  6. Marie on February 13, 2011 at 10:24 pm

    I’ve been wanting to start plants from seeds for quite a while, but the hardening off part has me deterred… I work full time, gone from 8 to 6. So how can I set the plants out for 2-3 hours? Any suggestions?

    I’m also in NE Ohio…


    Reply to Marie's comment

    • Susy on February 14, 2011 at 8:16 am

      I’d recommend putting them out in a shady spot in the yard while you’re away and them moving them to an area where they’ll get more sun after a few days. The thing you don’t want to do is to put them in the bright full-day sun all day their first day out. Even if you can just put them in the sun in the evening when you get home from work for a few days that will help. Maybe you can plan start hardening them off on Tues or Wed, then on the weekend you can give them a few hours in the bright mid-day sun. You can also give them a shade cloth or something for a day or two after you move them into the full sun while you’re gone at work, this will also help them adjust to the real sun. Even with a few days of hardening off that will help them adjust and you shouldn’t have too much trouble with sunburn since the sun here in NE Ohio isn’t quite a hot during the spring hardening off season.

      Reply to Susy's comment

  7. Fawn on March 26, 2011 at 6:16 pm


    I put my seedlings on the porch a couple of days ago to get them ready for the garden and forgot to bring them in after a couple of hours and they were not happy about it to say the least! (I live in Louisiana and the high is 83 today). The snap beans and zucchini were most affected because they had grown the biggest. I have been giving them a lot of attention since then indoors, including watering multiple times a day since the little pods they are in tend to dry out quickly. The seedlings seem to be recovering ok I just wanted to know if you have any tips for recovering seedlings from hardening off too fast to ensure strong, productive transplants. Thanks!

    Reply to Fawn's comment

    • Susy on March 28, 2011 at 8:29 am

      They should recover – plants like people become stronger when dealing with difficult circumstances!

      Reply to Susy's comment


This is a daily journal of my efforts to cultivate a more simple life, through local eating, gardening and so many other things. We used to live in a small suburban neighborhood Ohio but moved to 153 acres in Liberty, Maine in 2012.

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