How To Harden Off Seedlings (A Step-by-Step Guide)

Are you looking for a simple way to harden off seedlings before transplanting them into your garden? Then this guide is for you.

Hardening off is simply a process of getting tender, indoor-grown seedlings gradually accustomed to a new environment.

This is essential in transplanting your seedlings and preparing them for their challenges in the outside world.

how to hardening off seedlings for planting

In this article, you’ll learn the exact method we use here on the farm to harden off our “shaded” seedlings, including some common mistakes to avoid.

But before we jump to the step-by-step tutorial, let’s figure out whether this process is even worth the effort.

The Importance of Hardening Off Seedlings

First, hardening off is optional if your plants were introduced to the growing environment soon after germinating.

However, imagine walking outside after you wake up on a chilly morning – a bit shocking, right? 

It’s the same for seedlings moving from indoor or shaded growing areas to the outdoors. They need time to adjust.

Thinned Lettuce Seedlings

Failure to adapt to the different sunlight, winds, and temperatures can result in stunted growth or loss of the plant.

And since neither of us wants that outcome, let’s look at the simple tutorial.

How To Harden Off Seedlings (Step-by-Step)

Hardening off seedlings is a simple process. 

However, it requires knowledge of the type of plant and temperature in your area. 

That said, let’s dive into the first step.

Step 1. Research Your Plant’s Growing Requirements

First, I must point out that some crops grow best in cool temperatures, while others prefer warm climates. 

For example, lettuce is a cool weather plant, while tomatoes favor warmer temperatures. 

Usually, you can find this information on the seed package or online for the specific variety of plants. 

how to grow tomatoes from seeds

Step 2. Choose The Right Time

Once you know the ideal temperatures, you need to consider the time to sow the seeds and transplant them to the garden.

Ideally, you want to start hardening off seedlings about 2 weeks before transplanting.

As a result, you have to consider whether the forecasted weather is suitable for your crops.

when to plant tomatoes

Step 3. Select an Ideal Location

Next, find a spot close to the growing area to place the seedlings, tray and all. 

Remember, you want to expose the plants to the conditions they will encounter after transplant.

However, don’t expose them all at once. That’s where the next step comes in. 

hardening off seedlings on garden bed

Step 4. Increase Exposure To Outdoors Gradually 

Place your seedlings in the designated spot early in the morning for about an hour or two. Move them to a shaded area for the rest of the day.

Then, gradually extend their exposure time by about an hour every other day over the next 10 days. 

Note: You can leave your seedlings outside for the entire day if the sky is overcast, but keep an eye on them.
tomato seedlings harden off

Step 5. Monitor Weather Conditions

The weather can be tricky, so you must watch forecasts and pay attention to what’s happening outside.

Protect your seedlings from heavy rain or scorching sun. Carry them inside if necessary.

While you’re at it, watch out for pests. A simple covering or barrier works wonders but can defeat the hardening-off process.

Step 7. Observe Plant Responses

Your seedlings will “speak” to you through their appearance – you need to listen.

Watch for signs of stress, such as wilting or yellow leaves. 

And be ready to adjust the length of their time outside or water them if needed. 

tomato seedling in large pot

Step 9. Prepare for Transplanting

As the transplanting date approaches, you must ensure the plants are ready.

For example, the seedling should be able to happily stay outside the entire day and night. 

Once this is the case, you should make final preparations for the planting area for transplanting.

Note: I like to soak the seedlings in a dilute solution of leaf mold or liquid fertilizer on the day of transplanting to further reduce the impact of transplant shock.
healthy tomato seedling transplant

Common Mistakes to Avoid

The hardening-off process is relatively straightforward but may tempt you to cut some corners.

As a result, before you sabotage your hardening efforts, let’s look at some common mistakes and how you can avoid them. 

1. Abrupt Exposure

Don’t toss your seedlings directly into the blazing sun. Some will literally burn to a crisp. 

You need to gradually increase the exposure over a couple days. 

In some instances, you’ll even notice a thin protective wax-like coating forming on the leaves of some plants. 

2. Neglecting Seedlings

Weather changes can be tricky, which can cause plants to use more water than usual, possibly going dry.

As a result, you should periodically cast an eye on your seedlings, monitoring for signs of stress or dehydration.

Remember, in most cases, these seedlings are in tiny trays that can dry out unexpectedly. 

overgrown seedlings on hardening off table

3. Being Impatient

Again, it’s best to be patient. Hardening off can take up to two weeks and requires paying attention to your plants.

Of course, you’d like the process to finish sooner and get your plants in the ground. 

But an extra day or two acclimating your seedlings to the ground can save you time, money, and from frustration later. 

Final Thoughts

Thank you for taking the time to read this short tutorial. We hope you’ve discovered the ABCs of hardening off seedlings.  

Remember, hardening off helps to reduce transplant shock and makes your plant more robust and resilient to most of what nature throws at it. 

As a result, your effort pays off in vibrant, healthy plants and a garden that thrives all season long.

Now, it’s your turn! Apply the step-by-step guide, avoid common mistakes, and watch your garden transform.

If you’d like to learn more gardening skills, head to our Garden Tasks Page for a treasure trove of tips and tricks. 

close up of green pepper seedlings

Related Questions

1. How long does it take to harden off seedlings?

Depending on the plant and weather conditions, harden-off seedlings take about 7-10 days. This process starts with 1-2 hours outdoors, then gradually increases exposure until the plants last all day outside. 

2. Can you skip hardening off seedlings?

It is possible to skip hardening off seedlings at the risk of having them struggle outdoors. For example, skipping hardening off cabbages might lead to wilted or burnt plants in your garden.

3. What is an example of hardening off?

A good example of hardening off is placing shade-grown lettuce seedlings outside, gradually increasing exposure until the plant can comfortably remain outside all day. 


PennState Extension. Hardening Transplants. Accessed November 2023

RHS. Hardening Off Tender Plants. Accessed November 2023

University Of Maryland. Hardening Off Vegetable Seedlings for the Home Garden. Accessed November 2023

Illinois Extension. Starting a Garden: Hardening Off Indoor Seedlings. Accessed November 2023

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About Julien

Julien Kirton is the founder and main content creator at Micro Farm Guide. He has over 10 years experience in small-scale farming, and enjoys helping people build productive backyard farms using natural farming and other sustainable techniques.