Hardening off Seedlings before Transplanting (6 Easy Hacks)

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Hardening off seedlings before transplanting must occur in order for plants to acclimate to the outside temperatures and natural sunlight.

This process is time consuming but it’s often a labor of love. Or at the very least, a necessary evil.

However you feel about hardening off seedlings, it must be done. Best to embrace it and keep your garden growing and thriving!

Hardening Off Seedlings on the deck in the sun to get them ready for transplanting

If you don’t, your plants could shrivel and die, or their leaves might get sunburn. I didn’t know this when I was a first-time gardener.

Now I’m more than a few years in and doing my best to improve each season. And I’m happy to share some tips on how to harden off seedlings so you can transplant everything outside in no time.

Learn how to acclimate plants to outdoors for a successful garden this year!

Little Girl Helping Mommy Harden Off Seedlings on the Deck Outside

Hardening Off Definition

Hardening off is the process of acclimating plants and seedlings to the outside climate. Exposing seedlings to new growing conditions enables them to adapt to these settings slowly over time.

After hardening, plants are less likely to go into shock or suffer major issues getting used to the new growing environment.

Large spread of seedlings hardening off on the deck in the sun, lots of trays and pots and egg cartons of seedlings

Advantages of Hardening Off Seedlings

The hardening off process may seem tedious, but try to look at all the positives!

Here are some of the added benefits of hardening off before transplanting:

  • Plants Gradually Grow Accustomed to the Outdoors.
  • Brighter Sunlight Accelerates Growth.
  • Natural Wind Encourages Stronger Stems.
  • Soon, Plants Can Thrive Outside!
  • Your Family Can Help You, Making this a Memory in the Making!
Hardening off seedlings in trays and egg cartons on the deck in the sun - tomatoes, pumpkins, cucumbers, and more

How to Harden Off Plants before Transplanting

It’s easier than you might expect when hardening off seedlings before transplanting.

You simply need to get into a rhythm and try a few simple tips to add convenience!

Hardening off Seedlings in Egg Carton in the Garden
  1. On the first day, put your plants in the shade for one hour.
  2. For the second day, put your plants in the shade again, this time for two hours.
  3. Add an hour each day, keeping your plants mostly in the shade at first.
  4. You can begin to introduce some indirect sunlight a few days to a week into the hardening off process. Just be careful not to overdo it right away.
  5. Gradually increase the amount of time the plants are in indirect sunlight.
  6. Slowly introduce direct sunlight, just a little bit at a time at first.
  7. In 10 days, you may have your plants outside for as many as 10 hours with much of the time in the natural daylight.
  8. Continue to increase the length of time until you are comfortable leaving your seedlings outside overnight.
    (Remember to check the weather forecast carefully!)
  9. After two weeks, give or take, your plants should be fully ready to transplant. (I’ve heard some can go as quickly as a week, but I like to take my time to make sure the plants are good to go.)

Tips – The Easy Way to Harden off Plants

Try these simple tips to make hardening off seedlings even more convenient.

Hardening Of Seedlings in colorful pots in a Basin Container
  • Start hardening off seedlings in the shade and then add a little extra sun each day.
  • Put your pots in basins and bins to make them easier to tote.
  • Use a wagon to cart around your seedlings hardening off between shade and sun, inside and outside.
  • Don’t forget to check your plants regularly! Identify sunburn and leaf scorching early so you just lose a few leaves and not the whole plant. Or avoid leaf burns altogether!
  • Check the soil moisture. Water as needed. Do not let the plants dry out in their trays in the sun.
  • Watch the weather forecast. Avoid major downpours to limit mud and mess coming back into your home.
Hardening Off Seedlings in a Red Wagon in the Sun on the Deck


Hardening off means helping the plants adjust to the outdoor environment prior to permanent transplanting outside. Hardening is a process of gradually exposing seedling and plants to more sunlight and different temperatures across a span of days or weeks.

Typically, hardening off seedlings takes one to two weeks to complete the process effectively. Each day you will add time to the duration your plants sit outside.

Remember to check your area’s frost dates and local weather forecast before transplanting your hardened off seedlings.

Seedlings of 3 to 4 inches in height generally stand a pretty good chance of success when transplanting. You can certainly transplant smaller seedlings, too, but they may need more frequent watering and extra care.

Hardening off prepares the seedling for transplanting after it’s spent most of the time growing indoors or in another protected setting. The process helps plants acclimate to harsher conditions. Gradual exposure to more intense sunlight allows the leaves to toughen up and wind or breezes can help strengthen stems.

While acclimating the plants is recommended, your plants may still survive if you don’t properly harden them. After hardening, plants are believed to be less likely to go into shock or suffer damages from extreme temperatures or sunlight exposure. Still, even after shock, leaf scorch, and other issues from sudden exposure, plants may still bounce back in time.

Final Thoughts: Hardening of Seedlings

The hardening of seedlings takes time but brings many benefits to the plants, namely, getting them transplanted safely and soon.

Your plants will be much happier once they make it through the hardening off phase!

Some plants are more delicate than others. Use care with each type of seedlings you prepare for the big world.

And watch your frost dates and overnight lows!

You can also try these tips for Hardening Off Tomatoes to get your prized crops started off for a happy and healthy future of growing outside.

Enjoying a Glass of Wine while Hardening off Seedlings on the Deck in the Sun

By the way, if you are new to gardening or could use a little help hardening off seedlings from inside, be sure to check our post, Hardening Off Plants – Don’t Make These 7 Beginner Mistakes.

It gives tips for all the problems I’ve already experienced in my own gardening adventures so hopefully you won’t run into the same issues.

What are your favorite tips for the hardening of seedlings? Do you use any special equipment or techniques not mentioned here?

Please share your favorite tips or any questions you may have in the comments below. We always love hearing from you!

05.10.23 – Updated to freshen up content and added faq, reorganized a bit.

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