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How To Harden Off Plants

How To Harden Off Plants and Transplant Your Seedlings

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by Helen
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In order for various types of plants to grow and mature, they need to be transplanted into their permanent home.  This means moving them out of their warm, cozy environment where they grew from your seeds into delicate seedlings and introducing them to the world outside.  Therefore, it's essential to know how to harden off your plants before transplanting them into your garden or garden beds.

Moving and transplanting is a very stressful plant life cycle event.  Picture the delicate seedlings growing indoors in a climate-controlled environment; suddenly, they are moved outside into an environment with full sun, rain, wind, and varying weather conditions.

Transplanting Seedlings

Before transplanting healthy seedlings to a new environment, they must undergo a “hardening off” process.  This process involves exposing tender plants to sunlight, wind, and light rain.  The process causes them to toughen up and thicken the cuticle on their leaves.  The leaves lose less water once exposed to other elements and a new environment.

Outdoor temperatures should reach at least 45 degrees Fahrenheit before you start the hardening-off process.  Why should you wait?  For example, warm-season crops like tomatoes and peppers can be weakened by temperatures that are too cool.  Check the USDA Hardiness Zone Map to get an idea of when you should begin this process in your region.

After properly hardening off, new transplants are less likely to experience shock.  Transplant shock, also known as temperature shock, can occur when indoor seedlings die due to sudden temperature changes.  Between night and day, such as going from low temperatures to a sunny day.  This is especially common during seasonal transplanting.

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Why Should You Harden Off Plants?

When different types of plants are grown from seeds indoors or in a greenhouse, they thrive in their controlled environment.   Where the temperature is maintained, light levels are lower than outside sun, with minimal disturbances. However, once transplanted, these indoor-grown plants may not have the necessary defenses to withstand harsh outdoor conditions such as sunlight, rain, and wind.

To help seedlings build resistance, knowing how to harden plants before planting them outside is essential. Hardening off is a simple process that will improve the strength and health of your plants, especially when you transplant them into your outdoor garden. Therefore, hardening off your plants is crucial for their thriving growth.

How To Harden Off Plants

3 Ways To Hardening Off Plants

The time required to harden off a seedling depends on the plant type and temperature. There are three methods to harden off young plants.    Growing lettuce from seed is a great way to enjoy fresh, crisp salad greens right from your garden. With a few basic steps, you can grow lettuce from seed and enjoy delicious, homegrown greens all season long.

Starting seedlings indoors is a great way to get a head start on your garden and increase your chances of early planting success. Here are some tips for starting seedlings indoors.

1) Exposing The Plants To Longer Periods Outdoors

Gradually exposing plants to harsher outdoor conditions is essential to hardening plants for your garden. Start by taking the seedlings outside for short, monitored periods of time, for about 7 to 10 days prior to moving them into the garden. Choose a shady or sheltered spot outside your home or greenhouse, such as under a tree or on a porch. Leave the plants outside for an hour on the first day, gradually increasing the time by an hour each day until they spend an entire night outside.

To help the plants get used to different conditions:

  1. Take them out at different times of the day.
  2. Return the plants inside your greenhouse or home every night.
  3. After 2 to 3 days, move the plants from the sheltered spot into the sun, but return them to the shade in the afternoon.

If outdoor temperatures get warmer, keep an eye on the soil, as too much sun can dry it out, and direct sunlight can scorch the leaves. After 7 to 10 days, your plants should be ready for transplanting. Choose a cloudy day for transplanting and water the plants well. Letting your plants adjust to the outdoor environment is always a good idea. Check out this video for more information on how to harden off your plants before transplanting.

2) Placing The Plants In A Cold Frame

When it comes to hardening plants before transplanting them, we usually think of moving them directly into the yard. However, using a cold frame or a warm greenhouse can also be helpful. To harden off your plants using a cold frame, you can place the plants you want to transplant during the transition period inside it.

To do this:

  1. Move your indoor plants to the cold frame 7 to 10 days before you plan to transfer them.
  2. Ensure the temperature inside the cold frame does not drop below 50 degrees Fahrenheit, especially during cold winters.
  3. While your plants are in this warm and sheltered environment, check the soil surface and moisture level daily to ensure they have enough water.

Gradually increase the time you leave the cold frame open or turn off the heat each day. Start with 3 to 4 hours, then increase by 1 to 2 hours each day. Also, close the cover and turn the heat on during cold nights.

After 7 to 10 days, your young plants should be ready to be transplanted. When transplanting them, ensure the outdoor conditions are suitable, such as on a cloudy day, and the plants are watered well beforehand.

Using a greenhouse can also be beneficial for your plants. So, don't hesitate to make the most out of it! 

3) Not Watering The Plants For A Period Of Time

To harden your plants for outdoor living, you can withhold water for a period of time. The same effect can be achieved by allowing the seedlings to wilt. 

Two weeks before you plan to transplant your seedlings, start withholding water. Wait to water them until they begin to wilt. However, please pay close attention to the leaves and stems of the plants and keep them dry and wilting for a short time. 

Once the plants start to wilt, water them and wait for them to wilt again. After two weeks, your seedlings will be ready to be transplanted. When transplanting your plants, do it on a cloudy day and ensure you water them well. 

Remember, watering the plants daily is not the best way to harden them.

Things To Keep In Mind When Hardening Off

  • Gradually expose your plants to longer periods of time in outdoor elements and conditions to make the moving in and out process easier. You can use a wheelbarrow or a wagon to move the plants into the garage or porch quickly and easily. 
  • Protecting your seedlings from animals and pests like snails is also a good idea, as placing them on a table or somewhere they are not easily visible is also a good idea. 
  • Keep an eye on direct sunlight, which can cause the leaves to wilt or sunburn. If you live in an area with high winds, it's best to block the strong winds to prevent the tender stems from breaking.

Hardening off is crucial, especially when transitioning from a warm place to a location with colder conditions and cool nights.  

Final Thoughts: How To Harden Off Plants and Transplating Seedlings

Hardening off plants is vital in ensuring their successful transplantation. By gradually exposing them to outdoor conditions, plants can adapt to temperature, sunlight, and wind changes, which can help them establish more vigorous root systems and better overall health.

While the process may take some time and effort, it is well worth it to ensure the long-term success of your garden. So, make sure to take the necessary steps to harden off your plants before transplanting them into your garden or outdoor space.

By following the steps below on How To Harden Off Your Plants Before Transplanting, you can rest assured you're making the life cycle of your plants more robust, and they will be able to grow better, even if exposed to harsher conditions.

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