After you’ve started your seeds, how do you transition them to the outdoor garden? Also known as hardening off plants, this is a critical step to get your seedlings ready to go outside. In this post, I’ll share what you need to know to successfully transition your seedlings to the garden.
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Starting your Seeds
Before you can think about hardening off your seedlings, you need ensure you’re starting off with healthy seedlings to begin with. Ideally, you have started them off with a good grow light. Healthy seedlings are also spaced appropriately, only one strong seedling per cell. When you start your seeds well, you set yourself up for better hardening off and transplanting.
Not all seedlings will need this, but some seedlings will grow out of their small container before they are ready for the ground. I use a plastic cup that holds about two cups of dirt. I primarily do this with my tomatoes and peppers and sometimes other crops that outgrow their containers before it’s time to get them outside.
Hardening Off Plants
When you have a seedling that has been growing in a controlled indoor environment, you can’t suddenly put that seedling outside in the ground. You want to slowly prepare that plant for the outdoors.
Why You Should Harden Off Plants
When you start seeds indoors with a grow light or even in a window, the light is not the same as the direct sunlight it will experience outdoors. Your plant needs to adjust to full sunlight. It also needs to be acclimated to the wind. A plant that hasn’t been in the wind is not strong enough to withstand a gusty day. Even if you have a fan blowing on your seedlings inside (which I recommend), it is not the same as the wind and your plants need to grow stronger slowly. Temperature swings from night to day are another reason to prepare your plants.
My Hardening Off Process
Each gardener hardens off plants his or her own way, but this is how I get my seedlings ready to thrive outside.
I start 1-2 weeks ahead of my outdoor planting time. On the first day, I put my plants outside in a shady spot for about an hour. The next day I’ll increase the time to two hours and they may get a little more sun. Every day, they will get progressively more sun and time outside.
Early in the process, I pay attention to the outdoor temperature; I don’t want the temperature to change too much at the beginning of the hardening off process. For example, if my indoor temperature is 70 degrees, I like to choose a time of day when the outdoor temperatures hover between 65 and 75 if possible.
As they’re in the sun in these containers, I also pay close attention and keep them well watered. Plants exposed to sun and wind dry out quicker than those in your controlled indoor environment.
Further along in the hardening off process, after I’ve added hours each day and the plants have grown acclimated to the outdoors most of the day, then I start to think about nighttime temperatures. I won’t leave them outside in containers when it is near frost temperatures, but they do need to prepare for temperature swings.
For an almost hardened-off tomato plant, for example, I’ll only leave them outside when nighttime temperatures are in the 50s. For peppers, I wait until the 60s.
When to Transplant
After the hardening off process is complete, start watching the weather for opportunities to transplant those seedlings into the garden.
You want to help your young plants have as smooth a transition as possible. Think about the temperatures outside, including the nighttime temperatures, and avoid planting when you expect any extreme temperature shifts.
Related: When to Plant What
You may want to transplant on a cloudy day, though it’s not always possible. I often transplant my crops later in the day so they miss the direct heat of the early afternoon. If rain isn’t in the forecast for the next day, make sure you water them well after transplant.
There are several things to think about when starting seeds and hardening off plants to transplant them into the garden. Do you have any hardening off tips you’d add to my process?
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