Hardening Off: Give Your Seedlings the Best Start

Cucumber, Cilantro, Borage getting some sun without their floating row cover.

Cucumber, Cilantro, Borage getting some sun without their floating row cover.

March is coming to a close and here in Northern California that means it's time for me to get my seedlings outdoors. I've grown them under a grow light for the last 8 weeks in my garage and many of them are beginning to out grow their pots. But before I can put them into the ground I need to harden them off.

What is hardening off? It's a set of practices done to help seedlings which have grown indoors to successfully transition to outdoor conditions. Hardening off helps seedlings adjust slowly so they do not experience shock and you don't end up with weak or worse, dead seedlings.

There are a few ways to harden off your seedlings. I use two methods depending on the seedling species. With seedlings like cucumbers, squash, peas, lettuce, I will move these pots outside and place them under floating row cover or in a cold frame for a week or so. This protects them from strong direct sunlight and from major temperature changes. It also maintains a more consistent soil moisture level. 

Tomato, pea and Calendula seedlings hardening off outdoors.

Tomato, pea and Calendula seedlings hardening off outdoors.

With more delicate seedlings like tomatoes, most herbs and some flowers, I move the pots outside each morning around 10 am when the air has had a chance to warm up.

Day 1: Move your seedlings outdoors in a warm but shady spot for about 4 hours. Bring them back inside for the rest of the day and overnight.

Day 2-3: Increase the time your seedlings are outdoors each day by an hour.

Day 4-6: Move seedlings into dappled shade or direct sun, again increasing their outdoor time by another hour.

Day 7-10: Your seedlings should be ready to go into the ground. In this method, please be aware of soil moisture levels. As they sit outside and in the sun they will dry up faster. 

Squash, zucchini, and watermelon hardening off.

Squash, zucchini, and watermelon hardening off.

When you do plant your seedlings try to do so on a cloudy day and be sure to do a deep watering once they are in the ground. I recommend setting up a drip irrigation system (more to come on this) to help keep soil moisture constant and sufficient for your growing plants. 

Seedlings under floating row cover to harden off.

Seedlings under floating row cover to harden off.

If, like me, you have vertebrate pests to deal with (in my yard it's cats, skunks and raccoons) you may want to cover the beds with floating row cover to discourage digging, or you can prepare the bed prior to planting by covering the entire soil surface with permeable landscape cloth. Then simply cut x's into the cloth where you will transplant your seedlings. The soil will stay warmer and there is nothing for the animals to dig in. 

Brussels Sprouts seedlings growing through landscape cloth.

Brussels Sprouts seedlings growing through landscape cloth.

It may take a little more time than simply transplanting your seedlings directly. But hardening off really gives them a good head start, making them hardier and better able to fight off diseases and pests. Please visit the Facebook Group page, The Homesteader's Crafty Cooperative to post photos of your seedlings and your favorite ways to prepare your seedlings for life in the garden.