Hardening Off Indoor Started Plants

What is Hardening Off?

Hardening off refers to the process of gradually preparing a plant that was started indoors to survive (and thrive) in outdoor conditions that are colder, windier and brighter. This process usually takes 7 to 14 days.

Why is Hardening Off important?

When starting your garden indoors it is important to harden off your baby plants because the difference in intensity between the lights they grew up with and the sun’s direct intensity is huge! If your plants are not properly acclimated to the sun’s intensity it could potentially fry leaves and the entire plant. To protect itself from water loss and the UV rays, plants produce a waxy layer called the waxy cuticle, exposure to the sun helps stimulate this waxy layer. The length of time it takes for each plant to harden off may be different; more delicate plants may require a very slow hardening off process. Be sure to listen to your plants, if they start wilting, that is them telling you to slow down the hardening process. 

Exposure

Find an area in indirectly sunlight that is relatively protected from the wind- this is the perfect space to place your baby plants to introduce them to the outdoors. Pick a day that is above 7 degrees Celsius and is not terribly windy. The first exposure should not be for very long, about an hour will be enough to introduce them. During the next couple days increase the amount of exposure they get outside by an hour or two each day until they can spend the whole day outside in the indirect light, do not expose them to direct sunlight yet. If the temperature drops below 7 degrees then it is best to keep the plants inside that day. Keep in mind that your plant's tender young leaves are a tasty snack for herbivores so keep them as safe as possible. 

Increase Direct Sunlight

When your baby plants have passed the "shade living" test they can start to see some direct sunlight. Start off by giving them an hour of morning sun then return them to the shade. Increase the number of hours of direct sunlight each day starting in the morning. This is a critical time during hardening off as you do not want to expose them to too much direct sun too soon or the leaves and possibly the entire plant will scorch and sadly perish. If you notice some plants wilting or the leaves turning yellow during this process, remove them from the sun and let them recover. When the night time temperature stays above 10 degrees and the seedlings have had about a week of hardening off, they will be ready to spend the night outside. Ensure seedlings are well watered in case of temperature spikes during these times. 

Transplant 

After your seedlings have been outside and have been hardened off to the amount of direct sunlight that they will be receiving they should be able to withstand the stress of being transplanted into their garden or container. Choose your transplanting day when it is cloudy or partially so, if there are no cloudy days then transplant them in the evening or afternoon so they don't get too stressed all at once. It is important to water your plants well when you transplant them as it helps with soil settling around the roots and with stress. 

If these steps are followed, plants should survive the transplant and thrive in their new outdoor environment. If there are any tips, tricks or things that you do differently that you have learned in your gardening experience we'd love to hear about them in the comments below!