How To Properly Harden Off Seedlings

You did it! You finally decided to start your own vegetable and flower seeds this year instead of buying plants from big box stores. You’ve spent much of the last few months tending, watering and babying your new plant friends. It’s so exciting! Now it’s warm enough to plant them outside, so you go and give them a good home, kiss them goodnight, and come out to see them the next day.

Only to discover they’ve all withered and died on you! No!! 

A very crucial step you missed in your home gardening process was hardening off your seedlings. Don’t worry, I’ll walk you through the what’s, why’s and how’s down below. You’ll be a seed starting and gardening champion in no time!

What Is Hardening Off? Why Is It Necessary?

The term “hardening off” means to gradually introduce your seedlings to outside growing conditions. 

Think about it: they have spent the first several weeks being cared for so diligently indoors. They had perfectly comfortable lighting conditions. The only form of wind they had to endure might have been a brief one from a heater vent nearby. 

If you transfer your perfectly cared for little plants outside suddenly, where they are introduced to the harsh sun, strong winds and fluctuating temperatures, they’re not going to do very well. I’ve accidentally killed my fair share of seedlings from not giving them enough time to acclimate before, so don’t worry. You’re not the only one. 

Luckily, there are a few ways you can mimic outdoor conditions indoors to help acclimate them to real life. Once you get the plants outdoors, I have a few tips for you to ensure you’re giving your plant babies every chance possible to thrive. 

After all, your goal is to see these plants to maturity, right? I know I don’t grow a ton of tomato seedlings in my office just for the heck of it, I want to harvest tomatoes, dang it!

Indoor Modifications

Like I mentioned before, there are a few things you can do indoors to help prepare your seedlings for the outdoor life. 

First and foremost, you should check your lighting setup. Do your seedlings look really tall and leggy, maybe flopping over on themselves? That’s their way of telling you that they need a more direct source of light. A leggy seedling will not thrive once outside – any sort of wind gust will topple that thing right over. So start your seedlings off right by giving them a nearby light source, preferably directly above them. 

One of the main killers of newly transplanted seedlings is wind. Gusty, nasty wind! It’s always a bummer seeing plants snapped in half because of a wind gust. 

One way you can help prepare your seedlings for the inevitable gust of wind is run an oscillating fan nearby on a low setting. This will mimic a gentle breeze, and really help strengthen those stems as the fan hits them. 

I utilize both a fan and the free energy of an open window for my seedlings. You can also run your hands gently over their tops, as if you were petting them, to help them strengthen their stems as well.

As if I need to give you any more reason to play with your plants, huh?

The Indoor/Outdoor Shuffle

Once it starts to warm up enough outside to begin thinking about permanently planting your seedlings, you’ll need to start the official hardening off process. By now, your seedlings should be nice and strong, and tolerant of some wind. Good job!

Now it’s time to acclimate them to the harsh sunshine. 

It seems backwards that fresh, uninhibited sunshine could harm a plant, but it’s true. You can burn and scald their leaves if you transition them out too quickly! 

What’s this indoor/outdoor shuffle I mentioned? It’s something I’m sure many northern gardeners are used to by now: spending what seems like copious amounts of time putting your trays of plants outside in nice weather, then hurriedly bringing them in when a storm cloud rolls in and nighttime temps drop. 

We’ve been having a lot of unseasonably warm early spring days here in Colorado, so my plant starts have had some tastes of sunshine here and there. 

When you first start the hardening off process, you’ll want to place your plants in a shady or partly sunny spot, like underneath a porch awning or under the canopy of a tree. Pick a nice, calm day and plan to have them out there for about an hour. 

Or, if you’re more of a visual person, watch your plants and they’ll tell you when they’ve had enough. Look for the beginning signs of stress, when they just barely begin drooping. Then bring them in and let them recuperate a bit before taking them out the next day. 

Basically, you’re going to be bringing your plants outside for longer and longer periods of time. 

Once they’re holding their own in the dappled shade, start introducing them to a little bit of direct sunshine at a time. Same premise: don’t keep them out there for too long at first. Take them out of the direct sun if they become stressed. The next time they will be able to handle a bit longer. 

It’s a bit of a dance, really. And a bit of learning how to communicate with your plants. Learning to read them for signs of what they need, and adjusting their environment to suit those needs. 

All in all, and if everything goes accordingly, I plan on hardening off taking about a week. The key is to go slowly, don’t rush it and listen to what your plants need of you. If all goes well, you’ll be enjoying them out in your garden for months to come! 

As always, feel free to drop me a comment below with any questions, or email me with more in depth questions. You’ve got this!

Happy growing, 

Becca