Hardening Off Seedlings

Your seedlings that you started indoors are looking good and you are ready to plant them in the garden.  So you are thinking you will just take them outdoors and plant them directly in the garden right?  Not exactly.  Remember these seedlings were germinated indoors and are not acclimated to the outdoors just yet.  So you have one more step to go through before planting. 

Cucumber, Eggplant, Squash, Basil, Zinnia, Tomato & Pepper Seedlings

Hardening off is a process of slowly taking your seeds outdoors and allowing them to adjust to their new environment.  During this process plant growth slows and more food is stored internally in the plants increasing the thickness of their outer leaf layers. 

I like to think of it like this: my seedlings are still babies and need extra care and attention.  They are still vulnerable to the harsh sun and the changes in temperature.  Up to this point they have been in my home in a controlled environment with the same amount of light and a relatively predictable temperature.  It is now my job to help them adjust to the outside changes before they are planted so that they can survive.

Seedlings beginning the hardening off process in the shade

Here is how I went about hardening off our seedlings:

May 15th- First day I set out seedlings labeled as tender (see chart below)

DAY 1:  Find a protected/covered area and set your seedlings under this area for 1 hour. Then return them to your indoor seed starting area (ours is under lights in the basement).

DAY 2: Same process but leave them out for 2 to 3 hours.

DAY 3:  Same process but leave them out for 4 hours.*

DAY 4:  Same process but leave them out for 5 hours.*

DAY 5:  Same process but leave them out for 6 hours.*

DAY 6:  Same process but leave them out for 7 hours.*

DAY 7:  Same process but leave them out for 8 hours.*

DAY 8:  Let plants spend the night outdoors under the covered/protected area.

DAY 9 thru 14: Gradually increase the amount of time the seedlings are spending in the sun.  

*you can also gradually introduce the sun (starting on day 3) in the morning light for about 1 hour then pull them back to the shade for the rest of the time.  

(This process will take a least 7 days but could go on for up to 10 days depending on your specific zone).

I choose to just do this process for 8 days, but the closer you go to 10 days the better the chances of your plants surviving the transplant process.  Above all make sure you don't skip this hardening off process.  You worked hard to take care of your seedlings and it would be very disappointing to loose them at this point!

NOTE:  Be aware of the weather and temperature outside during this process. (See chart below)  If the temperatures are going to drop lower than the minimum temperature recommended for your crop bring them indoors.   

Recommended Minimum Temperatures

Hardy	40 degrees F	Broccoli, Cabbage, Onions, Leeks, Parsley
Half-Hardy	45 degrees F	Celery, Lettuce
Tender	50 degrees F	Pumpkin, Squash, Sweet Corn
Tender	60 degrees F	Cucumber, Muskmelon
Tender	65 degrees F	Basil, Peppers, Tomatoes