How to Harden Off Seedlings

Starting seeds indoors is a great way to get an early jump on gardening and save money, but what should you do once those plants are ready to go outside?

You just move them to the garden, right? Well, it’s not quite that simple.

Instead, you should put your seedlings through a process called ‘hardening off’.

Why Should I Harden Off My Seedlings?

Plants that are grown in an indoor environment have never experienced the outdoor elements: rain, cold, wind, moisture loss, and full sun exposure.

It’s a bit of a shock to remove a plant from the only environment it’s ever known and place it in a completely new one! Indoor seedlings do not have the proper defenses built up for the outdoors.

Hardening off will help your seedings gradually build up a resistance so that they are better able to withstand the elements. It is a simple process that will enable your plants to grow better and stronger when you transfer them to the garden.

One of the biggest mistakes a gardener can make is taking her plants directly from the indoors to the garden without any hardening off. Plants will go into shock and quickly die without this process.

When to Start Hardening Off

This will depend on two factors:

  • The size of your plants. They should be large and strong enough to plant outside. We don’t want to transplant tiny, weak seedlings into the garden!
  • The temperatures in your area. When is your last frost date? You can determine yours here. You want to start this process one or two weeks before your last frost date.

Tips For Hardening Off Seedlings

  • The first thing to do is to pick a shady, sheltered spot to begin hardening off your seedlings. We don’t want to leave them in direct sunlight or in an open space where they can be whipped by the wind and elements. I have a shady spot right next to the house that I use for hardening off. This will give the plants a bit of wind exposure while also keeping them out of the wide open.
  • Gradually reduce the amount of waterings a week before you start hardening them off. Don’t allow the plants to wilt, but preparing them for less frequent waterings is part of hardening off.
  • Bring the plants inside if the temperatures dip drastically during the hardening off period.
  • It is especially important to watch the nighttime temperatures. You do not want to leave your plant babies out if the temperature dips below freezing.

Hardening Off Schedule (Print It Off Here!)

Begin at one to two weeks before you plan to transfer the seedlings into the garden.

DayHours OutsideAmount of Sunshine
11-2 hoursShaded location
22-3 hoursPartly shaded location
33-4 hoursPartly shaded to little sunshine
44-5 hours45 minutes
55-6 hours1-2 hours
66-7 hours2-3 hours
77-8 hours3-5 hours
88-9 hours4-6 hours
99-10 hours6-8 hours
1010-11 hours8-10 hours
1111-12 hours10-12 hours
1224 hoursFull sunshine
1324 hoursFull sunshine
1424 hoursTime to plant!

This is the two week version of hardening off. You can reduce it to one week by simply doubling the amount of time they are outside each day. Be sure to watch them and make sure the environmental shift is not too much for them!

Happy gardening, friend!


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