/*! elementor – v3.12.1 – 02-04-2023 */
.elementor-heading-title{padding:0;margin:0;line-height:1}.elementor-widget-heading .elementor-heading-title[class*=elementor-size-]>a{color:inherit;font-size:inherit;line-height:inherit}.elementor-widget-heading .elementor-heading-title.elementor-size-small{font-size:15px}.elementor-widget-heading .elementor-heading-title.elementor-size-medium{font-size:19px}.elementor-widget-heading .elementor-heading-title.elementor-size-large{font-size:29px}.elementor-widget-heading .elementor-heading-title.elementor-size-xl{font-size:39px}.elementor-widget-heading .elementor-heading-title.elementor-size-xxl{font-size:59px}

What is “Hardening Off” my Seedlings? And Why is it Important?

/*! elementor – v3.12.1 – 02-04-2023 */
.elementor-widget-image{text-align:center}.elementor-widget-image a{display:inline-block}.elementor-widget-image a img[src$=”.svg”]{width:48px}.elementor-widget-image img{vertical-align:middle;display:inline-block}

If you’ve spent much time talking to someone in a nursery you have probably heard them say something about “hardening off” seedlings.  This is a pretty common term for someone who is working in the industry every day but it isn’t something that every layperson knows.  Hardening off is the practice of gradually getting your plants used to new conditions, usually from indoor conditions to the outside.

When you grow your seedlings indoors for the first few weeks of their lives, conditions are great! Your seedlings are happy living in a stable 70 degree room with lots of water and the perfect amount of light from a grow light.  The outside world is not nearly as friendly and if you plant your starts directly from the seedling bench into the garden the shock could kill them, even if the conditions are good.  

Growers and gardeners everywhere figured out a way to solve this problem.  If you gradually introduce your baby plants to the outside world they will have time to adjust to the new conditions and will be able to survive the transition. So, how do I gradually harden off my new seedlings? See my guide below.

How to Harden off Seedlings

Step 1) Plant your seedlings and grow them to a solid size. See our seed starting guide for more help starting your seeds.  This will depend on the type of plant but I like to see at least four “true leaves” on my plants before I start hardening off.

Step 2) Find a protected place outdoors.  You will need a location outside where you can set your seedling trays. It should be safe from animals, children, and other hazards.  It also needs a little bit of protection from the sun.  Setting your plants outside directly in the bright afternoon light or on the south side of a building could sunburn them.  Just imagine if you had been indoors all winter and then suddenly went sunbathing.  For most of us it would not end with happy skin. Dappled shade or some shade from the harshest sun rays will help to keep your seedlings healthy and happy.

Step 3) Start a routine of bringing your seedlings in and out.  To harden off your seedlings correctly you need to bring them outside and then back inside each day.  I like to place my seedlings outside in the morning and then bring them inside when the sun starts to set at night. Leaving them outdoors all day requires that they are put down in a protected spot. If you decide to only put them outside for the morning hours and then bring them inside before the harsh afternoon heat comes in, then a less protected spot is fine.  Whatever you decide, it is a good idea to set a reminder on your phone or somewhere you will notice so that you don’t forget about your plants! It is especially important to bring your plants inside before dark if the night temperatures are dipping below 50 degrees.  You don’t want to chill your plants.

Step 4) Gradually increase how long your plants are outdoors or how much harsh sun and wind they are exposed to. As the days pass your plants will start to get used to the conditions outside and can be exposed to more and more harsh sun and wind.  I like to put my plants in dappled shade under a tree or shaded by a blanket over my porch railing.  After about three days I will start placing the seedling trays further and further from the shade so that they get more and more sun.  If you decided to place your seedlings outdoors only for the morning hours, start leaving them outside for two hours longer every two days.  This will expose them to more and more of the normal outside conditions. 

Step 5) After about two weeks, leave your plants outside for good. After about two weeks your plants should be fine to stay outside for good, so long as the night temperatures don’t dip below much below 40F for your cool season plants like lettuce or below 50F for warm season plants like tomatoes.  Keep an eye on your night time temperatures.  If you have already planted your seedlings and an unexpected frost or chill comes, you might be able to save them if you cover them with a container or a blanket.

How do you like to get your seedlings ready for spring and summer outside?  Comment your questions and experiences below.  Keep up the great growing everyone!