If you have been growing your little seedlings indoor you are likely thinking about transplanting them into your outdoor garden. It’s a really exciting time but there is something you need to do before getting them in the ground. Read on to learn about hardening off your seedlings.
What is hardening off and why should we do it?
Hardening off is the process where you gradually adapt your seedlings to the outside world. Until now, your little plants have had a relatively comfortable life with stable temperatures, frequent moisture, and very little wind. Suddenly taking them from under grow lights to planting in the ground would be a huge shock and result is very sad, potentially dead plants.
The good news is that you can avoid disaster by gently introducing them to outdoor conditions.
How to harden off Seedlings
Preparation
Determine when you would like to transplant into the garden. For most crops this should be around the time of your first frost-free date. Here in Cleveland, that is around the beginning of May. Once you have that date, count back 12 days or so.
Keep in mind that some cool season crops like chard, lettuce, or onions can be put in the ground a little bit earlier than warm season crops like tomatoes and peppers. The same process is applicable to all crops but your timing is going to be dependent on what you are growing.
Day 1-3
Select a day where temperatures are at least in the upper 50s or 60s. Ideally, you would have a fairly cloudy day with very little wind. Since bright sun can burn the tender leaves, place your seedlings in a shaded spot for the first few days of hardening off. I usually put mine under my patio table or in the garage with the door open.
Once they are in place, set a timer for 90 minutes. After the time is up, bring them back inside. While they are outdoors, keep an eye on the weather and bring them in if there are any changes. My schedule doesn’t have me home until 5:30 or 6 pm on some days so I like to start this process in the early evening when it’s not quite dark out but the hottest part of the day is over.
For the next two days, bring your plants out for an additional hour each time. Don’t move them into the sun just yet. Watch for any signs of stress like wilting or changes in leaf color.
Days 4-8
Starting on day 4, gradually begin exposing the seedlings to sunlight. Move your plants into the sun for an hour and then move back into a shaded area for an additional few hours. Each day, increase the time in the sun by an hour or so and move back into the shade for an additional hour each time. By day 8, the seedlings should be in the sun for about 5 hours each day and returning to the shaded area for the rest of the day.
Keep bringing them indoors in the evening.
Days 9-12
At this point, the seedlings can start spending most of the day in the sun. With sunlight and wind comes the additional stress of moisture being lost relatively quickly so make sure you keep up with watering.
Look at the weather forecast and see what the nighttime temperatures will be. If it is into the 50’s or above then it will be fine to leave the plants out overnight. Otherwise, bring the plants indoors at night until it warms up a little bit.
When you are confidant that warm temperatures are here to stay, it should be safe to transplant into the ground or raised beds.
