Hardening Off

By Kymisha Montgomery, CGC Urban Agriculture Coordinator

Starting seeds indoors can be a tedious activity. It’s either revered or despised. From ordering seeds, reading seed packets, understanding days to maturity and knowing the sowing depth to purchasing (or making) quality seed starting mix, the whole process can be as time consuming as it is rewarding. With all of the time and money that you put into everything from quality lights to proper watering, some of us tend to forget a very important step to success: hardening off!

What Is Hardening Off?

No one likes to just jump into a pool of water without knowing the temperature (unless it’s a dare or we’re craving attention). It’s like that for plants, too! There’s a process called hardening off that some of us tend to skip or forget about when we’re starting seeds for our garden. It happens before we transplant our baby seedlings into the soil, and it’s like dipping your toe into the pool first to mentally prepare yourself to jump. Or better yet, it’s like the average early spring day in Ohio: You start out with a coat on, then a sweater, then just a t-shirt by late afternoon.

Why Harden Off?

Plants started indoors need time to adjust to full sun exposure, wind or fluctuating temperatures. Gradually exposing your plants to these elements can increase their survival rate and reduce shock by encouraging a strong, healthy plant. During the hardening-off process, your plants start to slow down their growth, allowing them to establish a healthier stem and root structure. When exposed to natural light during the hardening-off process, for instance, the natural waxes on its leaves thicken, which reduces water loss and strengthens the cell walls. By gradually getting plants acclimated to the elements outdoors over a period of time, we can decrease the chances of their leaves getting scorched by the sun or wind and possibly dying.

How to Harden Off

Over a period of one to two weeks, gradually bring your plants outside, first to a shady spot or on a mild, cloudy day in the afternoon for just one to three hours. Gradually increase the time outdoors and the amount of sunlight the plants receive over the following days. Be careful not to leave them out during the evening hours when the temperature starts to drop! Pay attention to the forecast to make sure your plants aren’t left outdoors below 45 degrees, especially if they are not frost tolerant. By the end of week two, your plants should be sturdy enough to stay outdoors and be transplanted into the garden.

It takes time and effort, but the strong plants that result from hardening off are well worth it!