How To Harden Your Seedlings For A Successful Garden

How To Harden Your Seedlings to better withstand the spring weather for a successful garden in your own backyard. Use this tip to start a backyard garden with plants you grew from seeds. 

Growing starter plants for your home veggie garden is a great way to make sure your plants have a strong organic start. Whether you live in the north where the length of your summertime is limited or in the south where summers reign most of the year, starting plants early can be both easy and a frugal way to garden.

But starting your plants indoors is only part of growing a successful batch of seedlings, you also need to prepare those plants for the weather in your area.

This post will show you how to harden your seedlings for a more successful garden. Exactly what to do and why you need to do it. 

Harden up your fragile young seedlings before planting them in your garden to ensure they get the absolute best start. Have strong, healthy and heavily producing plants this year!

When I first began growing my own plants from seed, I truly thought once the plants were big enough and the weather was warm enough then those plants were ready to go into the ground.

Unfortunately, I soon found out there was more to it.

That first year I lost quite a few plants because of an unexpected cold snap. Not so cold there was a frost, but much much cooler than my poor little seedlings could handle.

SLCG PRO TIP: This is important to take note of. It’s not just a frost you need to be wary of, but any large dip in temperatures. If you are not a weather watcher now, once you start gardening…you will be. By making it a habit of watching the temperatures you will be able to save your garden and your plant from any significant changes. 

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Little did I know I could have prevented all of this by doing one simple thing.

Taking the Time to Harden Your seedlings.

Luckily, hardening your garden plants is quite simple to do, so don’t worry if you are a gardening newbie.

Hardening your Seedlings – Prep Work

When you are starting plants indoors your success all depends on your weather timeline.

Harden your seedlings before planting them in your garden to ensure they get the absolute best start. Have strong, healthy and heavily producing plants this year!

Your timeline is based on where you live. This includes the weather, the seasons, and the amount of daylight in your area. This is called your gardening zone.

Once you know your zone you will know the best time to plant any plant in your area. Learn your zone and remember it, I promise you will need it often. You can refer to this Zone Hardiness Map to find your specific zone. This will help you to know when to start your seeds indoors and also when you can safely add your plants to your garden. 

A zone, also known as a hardiness zone is a geographic area defined to encompass a certain range of climatic conditions relevant to plant growth and survival. ~Source Wiki

The zone rules are a good rule of thumb to use for most items you plant in your backyard garden with a few exceptions. Onions are one of them. Since onions do most of their growing below the ground, they can go in just as soon as the ground is worked. Find out more HERE.


In Northwestern Pennsylvania I like to begin my plants indoors in my DIY (not so) sophisticated growing system. This allows me to get a jump on my seedlings so they are sturdy enough to handle our heavy winds. For our zone, it is best to start peppers in February and tomatoes in March. I will also start any vine plants like watermelon or cantaloupe in April.

When you watch that video, you will see that things are not magazine worthy in any way. And that is important to note. Use what you have and only purchase what you absolutely need to create your own setup. 

A few things to include are:

Grow Lights

Planting Trays

Planting Soil

And, if you choose to grow your delicate seedlings in a cooler area, you can invest in heated mats to set your plants on. I realize that these mats are a costly investment, an alternative is what I use, and that this thick plastic covering that will help to hold in the heat from the lamps where the plants need it. A small thermometer with a humidity reader included will help you keep track of the conditions you have in your setup. 

By starting your seedlings based on your specific zone, you will ensure that your plants will be a good size come spring when you plant them in the ground. 

Harden up your seedlings before planting them in your garden to ensure they get the absolute best start. Have strong, healthy and heavily producing plants this year!

For me, I came at this seed-growing time frame from trial and error. I used the suggested plant times found for my zone and kept pretty thorough notes in my gardening journal each year. I made a note of when I started my seeds and how big my seedling plants were come planting MY time which was in May for my zone. If the date needed to be adjusted I would make a note of my new planting schedule for the following year and put a note in my calendar file.

SLCG PRO TIP: To know if your plants are strong watch the main stem and height. You want plants that are sturdy in the middle with good healthy leaves throughout. Long bendy week plants may not do well in winds or heavy rains. 


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I also like to have a gardening prep and planting schedule written up that I can refer to each spring. From that schedule, I know my plants need to be in the ground sometime between the last week of May and the 2nd week of June to make sure they have plenty of time to grow and produce a healthy harvest.

I am sure this seems like all the bases are covered. Once you have a schedule and your seed starting timeline written down and ready to refer to you are all ready to go…right?

No, there is still one more thing you need to do before you put your seedlings into your backyard garden.

You will want to make a plan to harden your seedlings. To acclimate them to the cooler and damper air that is outside so they can better handle any late weather cold snaps that may hit unexpectedly.

Here are a few tips to keep in mind when hardening up your seedlings. 

Tip #1. Choose a safe place.

To harden your seedlings, you simply need to set them outside in a safe place that is out of the way of nosey critters or in our case, curious pets. (great tip if you happen to have a crazy Jack Russel that insists on getting into EVERYTHING.)

Harden your seedlings to build stronger plants

Tip #2. Choose a spot with good sunshine.

A sunny place is best for you to harden up your seedlings, but be careful. Too much sun can very quickly dry out your plants especially if they are still in those little seed trays.

Tip #3. Water frequently as needed.

Watch your seedlings closely and water as needed. I like to set a reminder on my phone for every hour or so. This little nudge just keeps me on top of things and helps me to remember my young plants. When my timer goes off I can go out onto our back patio and look for dry soil at the base of my plants. I like to use a watering can with small holes so I can water my plants without risking any damage. 

Tip #4. Watch for winds.

We live in a very windy area so this is always a step I need to include with any of my plants. Whether you live in a high wind area or not, you will still want to watch for ay high winds as well.

Here is a tip I use quite often. If you have a windy day you can still put your plants outside, just keep them close to your house for extra protection. If you have a corner on your patio this might be a good place for a windy day. You can also put your plants under a glass table or under a woven deck chair. This will allow your seedlings to still get some sun but the winds cannot hurt them.

Tip #5. Make it easy.

If you have quite a few plants to harden up, taking them in and out each day can be quite a task. To help, I like to put my flats on a gardening cart or wagon that I can easily wheel in and out of our barn or garage.

Harden your seedlings before planting them in your garden to ensure they get the absolute best start. Have strong, healthy and heavily producing plants this year!

This utility wagon works well too.

You can either allow them to sit out in the sun right on the cart or move them to a safer location if needed. 

How long should you leave your plants out in the beginning to harden? 

The answer to this is always to start out slow and work your way up. Our goal is to get your delicate seedlings acclimated to your weather. You can do just a few hours a day working your way up to the entire day and part of the evening as well. 

Tip #6. Start Out Slow

To start, place all of your seedlings outside in a protected area for a few hours the first day working your way up to full days. Be sure to watch the soil as seedlings in containers can dry out quickly in the warm sunshine. 

After a few days to a week, if your plants are tolerating the weather well you can let them stay out into the evening. This will help your seedlings become used to the drop in temperatures and the dew that will coat and water their leaves.  

Tip #7. Bring them in at night.

Each night, bring the plants back into the house, barn, shed, or garage so they are protected from the cold damp air until they become more used to the changes. At this point, your plants should large enough to no longer need the grow lights. Remember to use a cart or wagon if you need to make this part a bit easier. 

Harden your seedlings before planting them in your garden to ensure they get the absolute best start. Have strong, healthy and heavily producing plants this year!

Tip #8. Be consistent for best results.

Continue to harden your seedlings like this for up to a week increasing the time spent outside with each day. Eventually, your plants will become stronger allowing them to better handle those chilly nights.

SLCG PRO TIP: At this point, you will begin to see a noticeable change in your delicate seedlings as they begin to grow into strong plants ready for your garden. Remember to keep thorough notes of how you did your hardens and how your plants progressed. These notes will be a crucial part of your growing plan next season.

Once your plants are accustomed to your weather, you are ready to transplant them into your garden soil without the risk of damaging your plants. 

Please remember, if you get an unexpected frost, all of your plants will need to be protected. No matter how sturdy and strong your plants are a frost can and will do some pretty significant damage if any of our plants are left out unprotected. 

A good rule of thumb is to always watch the weather so you are prepared for anything that may happen. This includes heavy rains, strong winds, hail, and yes, frost. 

You can use this row cover to help protect any of your plants if there is a risk of frost threatening your area. You can use sheets in a pinch, but sheets can be a bit heavy especially for young and delicate plants so please keep that in mind. 


There is nothing better than fresh organic vegetables straight from the garden. Start your plants indoors with organic seeds, take the time to harden your seedlings, prepare your soil, and mulch your garden and you will have a bountiful harvest. One you can use to fill your winter pantry with.

Have a question on how to harden up your seedlings? Ask in the comment below! 


Transplanting tomatoes gardening tip



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