
If you’re experienced in gardening, you should be familiar with the term “hardening off plants”. Hardening off plants aims to adapt the plants from indoors to the wind, sun, and rain.
If you’re new to the hobby and are unfamiliar with the term, this article will provide you with knowledge for your future gardening experience. We will teach you how to harden off seedlings quickly!
The hardening off method should be applied to most plants that start growing from seeds. Learning how to harden off seedlings properly is a great start if you want satisfying gardening results.
Here are some tips for you to get started with hardening off your seedlings.
What Is Hardening Off Seedlings?
Essentially, hardening off seedlings is the transition period between seedlings growing indoors and mature plants growing outside. Since the conditions inside and outside can sometimes be extremely different, you will need to properly prepare young seedlings for the outdoor condition.
The preparation is done by gradually exposing tender plants to outdoor situations that can’t be found indoors, such as strong winds, extreme sun exposure, and rainy seasons.
When Should You Harden Off Seedlings?
The beginning of hardening off seedlings can be flexible depending on the plant type and conditions of the gardening area. On average, hardening off seedlings begins two weeks before planting seedlings outdoors.
For cold season plants, hardening off seedlings can take up to 4 weeks, so the hardening off stage can be started earlier.
Since the outdoor climate can be unpredictable depending on the weather forecast, you should always monitor the temperature. Having additional equipment, such as a cold frame, can help you easily protect the plant from an unpredictable environment.
Read Also : How to Harden Off Pepper Plants Properly in 4 Simple Steps!
How To Harden Off Seedlings Quickly?
Hardening off seedlings can be done quickly if the temperature around the plants is stable. The favorable temperature for hardening off seedlings is above 50 degrees Fahrenheit; you’re better off placing the plants indoors if the temperature is lower.
While the climate and seasonal weather greatly affect the plant growth transitions, we don’t always have to depend on climate.
There are two methods that you can choose to harden off seedlings quickly.
The first is to harden off seedlings by gradually exposing them to outdoor conditions. This method is suitable for those of you who like indoor gardening and have easy access to your outdoor spaces.
The second way is to use a cold frame. This is best for those of you who’ve got your own greenhouse separate from your house. Either way, the best method is the one that feels easiest for you!

How long does it take to harden off seedlings by gradually exposing them to outdoor conditions?
Hardening off seedlings using this method usually takes at least two weeks. In the first 2 to 3 days, you can start by placing your seedlings for 1 to 2 hours in an outdoor location protected from strong winds and direct sunlight. Don’t forget to bring the seedlings back indoors when the daily outdoor time is reached.
After three days, you can gradually increase the plant’s daily outdoor limit. Increasing the sun and wind exposure to the plants each day can train them to survive the harsh outside conditions. You may find it difficult to carry your plants in and out for the first week of this process.
Please do yourself a favor by using a wheelbarrow to easily move your plants indoors and outdoors.
Be sure to monitor the growth of the plants and keep them well protected. There’s a chance that the leaves could be damaged by the sun, wind, or even animals that eat the foliage.
Temperatures below 45 degrees Fahrenheit can threaten plant life as well. If the temperature is over 50 degrees Fahrenheit even at night, you can safely leave the plant outside for an overnight stay. You can do this step once the second week starts!
When the plants are growing well after two weeks of the transition period, they are ready to be transplanted outdoors into garden soil or a larger container. Don’t forget to regularly water the plants after you move them outside!
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How To Harden Off Seedlings in a Cold Frame?
The cold frame is a bottomless box that is made of wood, while the top is covered by some kind of transparent layer. In simple terms, it’s like a mini greenhouse, but you can easily close and open the top or lid.
This allows you to regulate the sun’s exposure to the plants by opening it during the day and closing it at night to keep them warm.

The first thing to do when you choose this method is to move your seedlings to a safe outdoor cold frame. Then you can leave the plants there until the hardened off stage is complete.
The key to successful hardening off seedlings is temperature, so make sure the temperature around the plants is at least above 50 degrees Fahrenheit. You can use an automatic heater on a cold frame if the temperature at night is low.
Once the plants are placed safely in a cold frame outside, you can begin to expose plants to the sun by opening the cover during the day. Start with 3 to 4 hours of gentle afternoon or morning sun exposures.
Increase the exposure time gradually each day to increase the plant’s tolerance to sunlight. Don’t forget to close the cover when the daily exposure limit reaches and at night.
Within 14 days, seedlings should be growing healthily and well trained to tolerate sun and wind. You can leave them out of the cold frame and replant them in your garden.
In this method, you can easily place the plants in a place where you harden them off. No need to move the plants since you already moved them outside on their first day of the hardening-off process. No need to bother bringing the plants in and out!
Perhaps, that’s all the important stuff about hardening off seedlings in general. Hopefully, those tips provided you with useful insight to sharpen up your gardening skills and make your experience even more valuable. Keep on gardening!
Since you’ve mastered how to harden off seedlings in general, it is time to try to do it with tomatoes!