You’ve started your seedlings or purchased plants from the greenhouse, and it’s finally time to plant them! In your rush to grow things you plop them into the ground and hope for the best, only to find your precious plants withered, burned, or looking scraggly at best.
What went wrong?
You, my friend, were probably unaware that plants need to be hardened off–a term to define the process of toughening up your plants to handle life outdoors. Thankfully it’s pretty easy to do, it just takes a little time and a little know-how.
Know Your Last Frost Date
The first step to properly hardening off your seedlings is to know the last frost date for your area. I like to use this finder from the Farmer’s Almanac.
You’ll then start the hardening off process a week before you intend to plant. For example, I typically plant my garden the third weekend in May, so I’ll start the hardening off process the 2nd weekend in May.
The one exception? My heat loving plants like peppers and tomatoes. I’ll start the hardening off process the 3rd week of May and set them out into the garden the 4th week of May, or even the first week of June.
Find a Shady Spot
The difference between the amount of light a plant gets outdoors and indoors is huge–even if you grew that plant in a south facing window. Seedlings need to start the hardening off process in a shady spot outdoors and slowly be allowed more light as the week progresses.
Yes, this means you’re moving your plants around a lot. You’ll also likely need to bring them indoors at night, especially at the beginning of the week or if it gets too close to freezing.
If your seedlings live in a temporary greenhouse that zips open and close, it’s probably fine to open the door during the day and close it up at night.
Protect From Wind too!
Harsh winds can also ruin your seedlings. Some gardeners run a gentle fan breeze on their seedlings indoors to toughen them up and make the stems stronger. You don’t have to do this step, but your seedlings should be hardened off in an area outdoors that is safe from strong winds.
If your seedlings are going into a garden area where there is no wind protection, try and use pallets or something to provide a temporary wind break to the area.
Cheat and Use a Cloche
A cloche is just a fancy word for a clear cover for plants. It can be something that you buy like these cloches, or you can cut up milk jugs. Whatever you use, they’re a great way to protect your plants and heat up the soil.
I also use mine to keep birds and unwanted pests away.
Do I have to harden off my plants?
Last year, somewhat by accident, I discovered a different way of making starter plants that doesn’t require them to be hardened off. I was trying out winter sowing in milk jugs for the first time and was curious if the method would work with vegetables. It did, and the resulting plants were already acclimatized to the outdoors and didn’t need to be hardened off.
This year I’ll continue to run experiments with more vegetables, but if you want to try it yourself, here’s how.
Plant Like This for Best Success
Finally, when it comes time to put your seedlings into the ground, there’s a few simple things you can do to give them a head start.
- Try and plant your garden in the evening or on a cloudy day.
- Protect taller seedlings with a cloche, milk jug, or large coffee can from the wind for a few more days.
- Wait until after the last frost date, and watch the weather to be sure it doesn’t go below freezing overnight.
- Put your hand in the soil. If it feels cold, it’s probably still not time to plant most of your vegetables.
Hardening off your flower and vegetable seedlings is a little extra work, but that week of effort will pay off big time with a garden that you’ll be proud of.
P.S. If you’re seed starting for the first time and wondering what to use with a grow light, I use a system similar to this seed starting kit. I also love this window sill kit if you’re using natural light.
Kristen is a former farm kid turned urban gardener who owns the popular gardening website, Shifting Roots. She is obsessed with growing flowers and pushing the limits of what can be grown in her zone 3b garden. She also loves to grow tomatoes, but oddly enough, dislikes eating them raw.