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How to Successfully Harden Off Your Young Plants and Seedlings

Did you know that your overwintering plants and young seedlings need to acclimate to the outdoor elements before planting them in the garden? Follow along as I walk you through the process of hardening off your seedlings and plants before transplanting them outside.

Hardening off indoor plants is the transition period from a controlled environment to harsh outdoor elements. Acclimating young plants and seedlings is the best way to help them become accustomed to the natural environment.

hardening off seedlings and plants

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I’m a self-taught hobby gardener, not a Master Gardener. Everything I share with you on my blog is my personal opinion and things that have worked for me personally.

hardening off seedlings and plants

What is Hardening Off?

Hardening off your plants and young seedlings is when you introduce them to gradual exposure to outdoor conditions, such as wind, sun, and temperature fluctuations. This process helps tender plants and seedlings acclimate to the outdoor environment to survive and thrive when transplanted in the garden.

This is done by gradually increasing the time your plants and seedlings spend each day outdoors, starting with only a couple of hours the first day and eventually building up to a full day.

Many new gardeners skip this step, not knowing that their indoor seedlings and plants need to get used to the outdoor growing conditions after being sheltered for so long. I was one of those new gardeners, by the way.

seedlings hardening off outdoors

Why is Hardening Off So Important?

Hardening off your young plants and seedlings is an important step in the growth process because it prepares them to withstand the elements of the outside environment.

This process allows the plants to slowly acclimate to the temperature and light changes as well as helps to reduce the risk of transplant shock, which can lead to poor growth and even death.

Hardening off your newer plants thickens the cuticle on the leaves, so they lose less water when exposed to the elements.

geraniums hardening off outdoors

The Process of Hardening Off Plants and Seedlings

Each day, your plants and indoor seedlings move from their existing indoor space to a location where they can tolerate more hours of exposure to outdoor conditions each day.

It’s important to ensure you water the plants and keep them from drying out while going through this process.

inside the greenhouse with geranium plants and seedlings

Introduce Your Plants to the Outdoors

Begin the hardening-off process 7-10 days before transplanting seedlings or plants in the garden. Most seedlings are typically planted outdoors in spring after any risk of frost has passed. However, cold-hardy plants can be planted outdoors 2-4 weeks before the last frost date.

When the spring temperatures are above 45°F, set the seedlings in a sheltered and shady spot outdoors, protected from direct sunlight and wind for one hour on day one.

Make sure you’ve watered the plants thoroughly before bringing them outdoors. Move the seedlings back indoors when they’ve reached the time limit.

geraniums hardening off outdoors

Increase Outdoor Time Gradually

After placing the plants in a protected spot for 1-2 hours on the first day, slowly increase the amount of time each day after. Bring the plants in at night, especially on cool nights when the temperature drops below 55° F.

Gradually move the plants outdoors each day over several days, introducing them to increasing amounts of sun and wind each day.

When introducing the plants to direct sunshine, move them after 10-15 minutes of direct sunlight the first day and gradually increase the time each day. During this time, monitor your plants for sun scald or other signs of stress, such as wilting or yellowing leaves.

The length of time a seedling needs to harden off depends on the type of plant and temperatures outside.

When to Leave Outdoors Overnight

If temperatures remain at least 50°F in both the day and night, the seedlings should be able to handle increasing amounts of sunlight and can be left outdoors overnight.

 sweet pea seedlings

Tips to Make Hardening Off Easier

The Best Conditions for Hardening Off Plants and Seedlings

My best tip for hardening off plants is to check your weather forecast before you place seedlings outside each day to acclimate.

Strong winds and heavy rains can be quite damaging, so you should wait until the weather is calm and dry before starting the process of hardening off your plants.

The best time to harden off plants is in the morning or early evening when the temperature is cooler. You want to avoid the heat of the day when the sun is intense.

hardening off seedlings and plants

Water Your Plants

When watering your plants during hardening off, it is important to increase the amount of water they receive each day gradually. You should start by watering the plants lightly and increase the amount of water as they become more accustomed to their new home.

Water the plants until the soil is moist but not soggy. Avoid overwatering to prevent root rot and other issues.

transplanting seedlings into the garden beds

Transplant Your Acclimated Plants and Seedlings in the Garden

After 7-10 days of acclimating your plants to their new environment, they should be ready to transplant into the garden.

Avoid planting on a sunny day, and pick a cloudy day instead. Early mornings and overcast days are best to keep the plants from going into shock. Water thoroughly after planting.

hardening off seedlings and geraniums

Hardening off your seedlings and plants is an important step before transplanting them from indoors to garden beds in the spring. It can be hard work moving trays of plants in and out daily, but it is a great start to a healthy garden.

Not only does acclimatizing help to reduce the risk of shock or transplant failure, but it’s a great way to allow your plants to adjust to the changes in their environment and the harsher elements of outdoor life.

Thanks so much for following along. Comment below if you have any questions or other info about hardening off your seedlings and plants.

Until next time,

Happy Gardening!

seedlings in pots

It’s always fun to see what gardeners do in other parts of the country. My good friend, Stacy at Bricks ‘n Blooms, lives in New Jersey and is also starting to acclimate her seedlings to the outdoors. Take a look at some tips she has for hardening off her plants.

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  1. I have to tell you, it’s a lot of fun going through this process with someone. Especially when you live so far away, I love seeing how different our growing times are different.

  2. Your seedlings look amazing! I am ready to put my snapdragons and sweet peas in the ground this week. And then I’m starting to harden off a few others before the onslaught of seedlings makes their journey to the outdoors. So fun! Can’t wait to see your garden this year! It’s already off to a great start!

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