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How to Harden Off Seedlings

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If you’ve planted seeds indoors this winter with the hopes of growing your own garden plants, then you may be wondering how to get them ready for the outdoors. Sending your seedlings off into the great big world of the garden can seem daunting.

How do I not kill these “baby” plants? Are they mature enough? Hardening off seedlings is what you’ll need to do to ensure they transition into the outdoors without going into shock. Avoiding transplant shock will help your plants thrive in their new space.

harden off seedlings

Why Harden Off Seedlings?

If you’ve taken time to start seeds indoors, then chances are you’ve spent time nurturing those seedlings, and you want to make sure they live as they transition outside. To harden off seedlings isn’t a difficult task, but it does require a few steps.

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Just dropping seedlings into the garden, especially at the beginning of spring, when the weather may still be temperamental isn’t a great plan. In fact, gradually exposing seedlings to the outdoors is what hardening off seedlings is all about.

When seedlings are hardened off, they are exposed to the wind, sun, and possibly rain gradually. This changes the plants physically. The leaves will develop a thicker cuticle, making them hardier with less moisture lost. So new seedlings, especially those started indoors or in a greenhouse or cold frame, really do need a hardening off period.

How to Harden Off Seedlings

When to start? Begin the process of hardening off seedlings when the weather no longer holds the danger of frost. That will vary for each region, so be sure to check out The Farmer’s Almanac frost guide if you’re not sure. Now onto the steps!

  1. Begin by placing your new plants in a shady spot outside for 2-3 hours the first day. (Direct sun outdoors is much more intense that a sunny place inside your home.) hardening off seedlings
  2. Bring your plants in after their time outside, and be sure to keep their soil moist. Weather conditions outside may cause them to dry out a bit more quickly. Remember to water at the base of your seedlings, not the leaves. 
  3. Gradually add an hour of outside time each day, slowly exposing them to more sun. After 7 days of this gradual exposure to the weather, your plants should be toughened up and ready for transplant! This can be a transplant to your in-ground or raised bed garden or to an outdoor container. hardening off seedlings
  4. Be sure in the days that follow that you check the moisture of your plants. You don’t want them drying out and all of your hard work going to waste. They don’t need to be doused, but be sure the soil doesn’t stay dry for long. Drying out between waterings isn’t a bad thing for most plants, but since these babies are just starting out, don’t let them go too long between waterings.

Don’t Give Up on Starting From Seed

If your first attempt at growing your own seedlings ends up in a bust, don’t give up! Growing seedlings indoors can be a bit of a challenge at first, but you can get the hang of it. Try these egg carton starters if you need an easy method first. 

Learning to grow seedlings will save money, and you’ll know exactly where your plants came from… you! Buy good quality seeds, such as those from True Leaf Market, Eden Brothers Seed Company, or Baker Creek Heirloom Seeds. Quality seeds make all the difference.

And once you have your feet wet starting your own seedlings, you can jump into saving seed for the following year. It’s super simple! Here’s a tutorial on how to Save Tomato Seeds or saving basil seeds. 

Good luck hardening off your seedlings this year, and I hope you have a fantastic spring garden season. Happy Gardening!