Before you set your seedlings out in the garden, you must go through the process of hardening them off. Hardening off seedlings just means that you’re gradually exposing them to full sun over the course of a week or so.
This is important to prepare our seedlings for the harsher environment that exists outside their cozy little space in your home.
Hardening off seedlings – why go to the trouble?
The whole point of starting plants from seed is to grow the healthiest vegetables for your garden. But all that work could be ruined if you don’t go to the trouble of hardening off.
Transplants that aren’t gradually weaned outside can be stunted, slower to produce, or even die. They need a gentle transition into direct sunlight and wind.
If you don’t harden them off, they’re susceptible to sunburn, stem breakage, and drying out which leads to all the problems mentioned above. Fortunately, hardening off is not difficult and doesn’t require any special equipment or gardening space.
When to start hardening off seedlings
You’ll want to start the process of hardening off at least 1 week prior to planting in the garden. You can definitely take longer, but any shorter and you could have trouble.
This timing should also be after transplanting and before your planting date which depends on your frost dates. For example, 1-2 weeks before your last frost is ideal for hardening off tomato seedlings.
How to harden off seedlings
To harden off your seedlings, simply move them outdoors for 1-2 hours for a few days. Start by placing them where they will receive indirect light such as in a greenhouse or under a porch or eave.
If it’s a particularly sunny day, they should sit in the shade at first. Too much sun too fast will burn the leaves in just a couple of hours. If it’s cloudy out, they can sit without cover. Overcast days in early spring are perfect for hardening off tomato seedlings.
If you don’t have any indirect sunlight and it seems too harsh to you, it probably is. Either prop up some shade or shorten their time outside to about 30 minutes for a day or two.
After a couple of days in the shade, gradually move them and extend their time outside by 30 minutes to 1 hour until they can tolerate 8 hours of full sun per day.
Hardening off problems
The most common problem with hardening off is the burning of your plant leaves. Sunburn causes thin papery white patches on your plants’ leaves (click here to see a picture). If your seedlings get some sunburn spots on them, don’t panic. Give them a day or two to recover indoors and then start over.
Another issue can come up if your seedlings get dried out from the sun and wind. Remember to give them a good watering before and after you set them out in the sunshine.
Seedlings are never too young to spend a bit of time outside, and a breezy day can be great for strengthening their stem. But very young seedlings with few leaves will need extra care to make sure they don’t get sunburned or dry out.
Once your seedlings have been hardened off, you’re all set to plant them out in your garden!
How long for hardening off seedlings?
It takes about 10 days to harden off seedlings, but you can push it to 7 days if you’re in a rush or take as long as you want. While you’re waiting for them to harden off, prepare your garden beds or containers for planting.
Once they’re completely hardened off and last chance of frost has passed, you can transplant your veggies into the garden. If you’re planting out tomatoes, make sure you know what goes in the planting hole.
And here’s our favorite method for planting hundreds of veggie plants!