An important part of growing your own seedlings is hardening off your transplants. Don’t skip this step or you risk losing your transplants completely!
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You have dutifully cared for your new seedlings indoors for 6 weeks and you have a tray full of beautiful plants that look ready to head out to the garden. What now?
There is one more step in the seed-starting process that you shouldn’t skip.
Hardening off your transplants
Hardening off your transplants is the important final step before planting your seedlings in the garden. For the last 6 to 8 weeks your seedlings have been growing in near perfect growing conditions.
If you have done your job right your seedlings have been receiving plenty of water, light, and nutrition. They have also been growing indoors with very moderate temperatures and no wind. All of this leads to very healthy starts but they are also a little pampered and tender.
The process of hardening off your transplants slowly prepares your new plants for the harsher conditions out in the garden. Skip this step and you risk causing a shock to your plants from which they may never really recover. Hardening off your seedlings is accomplished by slowly exposing your seedlings to the conditions out in the garden.
When to start hardening off your transplants
Start hardening off your transplants at least a week to ten days before you intend to plant them in the garden. For the first 2 or 3 days bring your seedlings outside for only a few hours, at the most 4 hours.
If you are hardening off your seedlings in the cool spring then these first few days could be directly in the garden. If you are hardening off your seedlings in the hot summer or fall you may want to make those first few days under a shady tree so the plants can first get used to the heat with protection.
As the days go on continue hardening off your seedlings by increasing the amount of time they spend outside each day by a couple of hours per day.
If you are hardening off your seedlings in the early spring be sure that some of the time spent outside also includes time at night so your plants can adjust to the cold nighttime temperatures as well.
How long should you harden your transplants?
I usually shoot for at least a week to ten days of hardening off time. Be sure to include hardening time in your overall calculations of time for your seedlings.
You want most seedlings to only spend about 6 to 8 weeks in pots, any more time than that risks your seedlings becoming root-bound in the pots. That 6 to 8 weeks must include the hardening off time so start setting your plants out at the 5 to 7-week mark.
While your hardening off your seedlings you need to continue watering and fertilizing as you normally would. In fact, be extra sensitive to the water needs of your seedlings while they are hardening.
Those small pots don’t hold a lot of moisture and can dry out quickly on a hot or windy day. So be sure you check the condition of your plants often while they are outside. Once your seedlings have been hardened off get them out of those restrictive pots and into the garden!
Remember hardening off your transplants is a process you don’t want to skip. Doing it creates stronger and healthier plants for your garden. In fact, I recommend hardening off store-bought seedlings for at least a week as well!