How To Harden Off Tomato Plants! Top 3 Most Efficient Methods

Hardening off tomato seedlings

Starting a tomato garden is so much fun. It is especially even more exciting if you grow them from seeds. They’ll begin to germinate, the stems grow, and the leaves appear! Then, when the time comes, you can harvest them. It is magical.

However, sometimes, after a while, your tomato seedlings might suddenly wilt and die even though there is nothing extreme or strange that you do with the plants. Annoying, is it not?

This phenomenon happens because you did not harden the tomato seedlings off before you replant them. What does it mean? And do you know how to harden off tomato plants properly?

What does harden off mean?

Hardening off is a way to prepare seedlings for replanting. Replanting is the technique of moving a plant from one location to another, so plants can grow more optimally.

Seedlings that were raised indoors or in a greenhouse are not used to harsh outdoor conditions. Hence, before we move the young plants permanently, we need to acclimate the plants to the extreme day and night temperature changes. You also have to lower the humidity, exposing them to wind and direct sunlight.

Hardening off tomato seedlings.

Tomato plants can get a fright if they are suddenly exposed to extreme outside conditions. If you do not harden off tomato plants, the outside condition can damage them.

This step does not happen overnight. We need to gradually introduce seedlings to the outside condition over one to two weeks. The plants will thicken, and their leaf structure will change. This process of toughening up and building resistance to the environmental condition is known as “hardening off”.

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Best time to harden off tomato seedlings

Tomatoes are warm-weather plants and very fragile at this stage of growth. You should start hardening off the plants on clear days, with no wind and no rain.

You can start exposing your tomato seedlings to the outdoors around 2 to 4 weeks before the date you plan to replant them outdoors.

You can move the plants after they have germinated and have at least one set of leaves beyond the cotyledons. The cotyledons are the first set of leaves that come up after your seed germination, which usually will fall off after the plant has matured.

So, if another set of leaves has already appeared, you can start to harden the seedlings off.

Read Also : How to Harden Off Seedlings? The Best Way to Make Your Plants Grow Strong!

How to harden off tomato plants effectively?

There are several ways to harden off tomato plants. You can easily follow these ways.

1. Move them gradually

You should conduct the moving process slowly, over 1 to 2 weeks. The rule is one hour outdoors on day one, two hours outdoor on day two, and so on until the plants are outside for the entire day.

No need to hurry. Go slow and cool. On their first day, place the tomato seedlings close to the house, in a protected area, so it is safe from strong wind.

Do not put them out in direct sunlight and windy place. Young plants are vulnerable to sunburn, and a strong gush might break their roots and leaves. Such unideal conditions will do a lot of damage.

On their second days, do the same treatment but with a slightly longer duration. Repeat the steps for a few days.

Move seedlings gradually to harden them off.

Do not forget to check them every hour. If they are looking sad or wilted, bring them back inside. You should pay more attention because the plants will dry out much quicker outdoor, so adjust your watering accordingly.

Your plants may start to look a bit ragged. Even a gentle breeze can affect them. Take it easy. Your plants will recover by themselves and begin to get stronger. If it is a windy day, it is better to keep the plants inside. You can use a bamboo stick or chopstick to support and keep them upright.

After a week or so, you will notice the plants turning a darker green, and their stems are becoming stockier. It usually takes about 7 to 14 days to get fully hardened off. 

If you do it gradually, add more sun intensity to the hardening-off area each day. Of course, they should be able to take full sun, rain, and gentle winds over time.

2. Use a fan

Blowing young tomato plants with a fan will help them grow stronger. That way, they have a chance to stand up even against winds. A fan can replicate the same air movement that happens naturally outdoors.

Alternatively, you can put the seedlings near a window that gets regular gentle breezes.

You can also achieve similar results by gently tapping or shaking your plants regularly, but it is not effective and impractical. It would be very tiring to tap your plants regularly. Just use a fan, does it all the time!

How to harden off tomato plants method.

A fan will influence air circulation. It reduces moisture, and it’ll make the area dryer. It helps prevent microorganisms from overgrowing in your seedlings. A balanced number of microorganisms is awesome for your soil, but an overabundance of the wrong ones can cause disease, which will kill the plants.

Hardening off is about getting plants used to rain, sun, temperature, and other factors. Strong wind is actually one of the elements that can really cause the most damage to new seedlings.

Using a fan will dramatically reduce the hardening off time. Since your seedlings have been in the breeze area since birth, they know how to hold their own. You just need a few days to introduce your seedlings to the outdoors, and you are ready to replant.

This method is one of the best ways of how to harden off tomato plants quickly!

3. Use a cold frame

Serious gardeners who harden plants regularly usually will use a cold frame. It works like a simple greenhouse to give your new tomato plants more protected space while they adapt to life outside.

After you have hardened your plants in the cold frame, you can replant them in the outdoor garden.

You can design a basic cold frame using a 4-sided box with an open bottom. The top is clear or transparent.

The frame should be 20 inches to 2 feet in height, so it has room for your plants to grow and also to allow for adequate airflow beneath the lid.

A cold frame can be a good way to harden off tomato plants.

Lay it out in a sunny area with tomato seedlings inside. As the day cools off in the evening, you have to close the lid to protect your little plants from the chilly night air.

Do not keep the lid closed during the day, especially when it is hot. Just think about what happens inside your car when the windows are closed in the summer. Your seedlings might get cooked!

A cold frame must have a lid, at least enough to vent out the heat during the day. Check on your plants regularly, or even leave a thermometer inside the box so you can keep an eye on the temperature.

The method of how to harden off tomato plants using a cold frame is simpler to do. But, be ready to do some DIY, building the enclosure. Once you’ve set it up, it will last for a long time!

Do not hesitate to harden off your tomato plants! We assure you that your tomato plants will grow more strongly and provide you with a satisfying yield once the harvest time comes!

Knowing how to harden off tomato plants will be beneficial for someone who is about to start gardening! You need to master this basic skill so your tomato plants can live and grow properly.

Here is the next gardening skill you need to learn! Find out how to grow eggplants from seeds!