How To Harden Off Seedlings

You've planted your seeds and taken great care of them inside - don't let your hard work go to waste. Here's how to harden off seedlings to ensure they do well once planted outside!

As a beginner gardener I was so cute. Hey, let's throw a bunch of seeds in some dirt, leave them outside and they'll grow right? And not only will they grow, but they'll produce soooo well that I'll be drowning in homegrown produce. Ha! I had so much to learn. But that's my job now - to tell you the mistakes I made and help you learn from them so that you will actually have the problem of too many fresh veggies from your garden!

We've already learnt that starting seeds indoors is the best way to give them a great start in life. Now we are at the stage where they are ready to start being introduced to the big wide world outside. But slowly is the name of the game here. We've been babying these little seedlings for so long now, and we won't achieve anything by just flinging them out of the nest and hoping for the best.

To make sure that your seedlings are ready to be planted in the ground when the time comes, you need to slowly acclimatize them to outside conditions - wind, rain, hot sun, insects etc. By doing this in stages, they will have time to adjust and will be ready to face the world on their own once we're done (anyone else feel like we are raising children here?)

I work on hardening off my seedlings for about a month before I plant them. You can do it faster if you need to, and you can certainly take longer but by the time my seedlings were big enough to be going outside it was about one month before the time I would be planting them.

4 weeks before planting outside

So your seeds have been inside, they've germinated and have been sitting on a sunny windowsill while they grow. Awesome! I bet they're looking great. The first step in hardening off your seedlings is to take them outside for a few hours on a nice calm sunny day. That way they are exposed to outside weather, but the best possible conditions for them. In an ideal world you would have a week of perfect weather and you could do this for a few hours each day, but let's be real here. If you are working full time and it's raining, this is probably not going to work for you! So start over the weekend or when you are going to be home and leave them outside for as long as you can. Pick a nice day and if you need to leave them out all day, this won't be a problem.  I would just avoid leaving them outside for extended periods of time if you think the weather might turn nasty.

The best place for them is still somewhere reasonably sheltered. I have mine on our picnic table which is up on our front porch. It gets a lot of sun, a little bit of wind and if it really rains they would get slightly wet but not drown. Perfect!

3 weeks before planting outside

This is when they've had a bit of a taste for outside life and now you start to toughen them up a bit. All day is fine, a light breeze is fine, and even a little bit of rain. It's still better for them to be in a sheltered spot and definitely still bring them inside overnight but they can handle the full day outside now. I still bring them inside and give them a good water each night as being in the sun can dry them out quite quickly. At this stage I also start adding some Seaweed and Fish Fertiliser to their water. This gives them a good boost and will really benefit them down the track.

2 weeks before planting outside

It's time to start leaving them outside at night! At this stage I will leave them outside overnight but still under shelter. You can get mini greenhouses that are small enough to sit on your deck or next to your house but you can also use what you have to make a makeshift greenhouse for them. Rig up some sort of small frame and cover it in plastic or a light material, sit them under a table or on the tray under your BBQ and wrap plastic or material around that or even put rubbish bags over them. This will act as a protector against slugs, snails and if there is still any chance of a frost. But keeping them up off the ground if possible - so on your deck or picnic table and close to the house, preferably under the eaves of the house is ideal. Then uncover them during the day and leave them out.

1 week before planting outside

By this point they are almost ready to be planted outside so can be left outdoors overnight uncovered. I still keep them close to the house at this point but leave them in the same position during the day and overnight.

Once you have gradually hardened off your seedlings, they will be ready to be planted out in the garden! Like I said, this process can definitely be sped up if necessary - I think most people spend 7-10 days hardening off their seedlings but I planted my seeds super early and figured I may as well take my time.

If you have a greenhouse

If you are starting seeds in a greenhouse I would follow the same plan but probably over a shorter period of time. Unless you are going to be planting your seedlings in a polytunnel or tunnel house they still need to be exposed to outside conditions for at least a week before putting them in the garden.

Seedlings that will be planted inside

For the seedlings that I'm planning on planting in the polytunnel (which is significantly warmer than outside all year round) I take them outside during the day to begin with and then simply start leaving them in the polytunnel during the day and overnight from about 2 weeks before I plant them. They still need to get used to being outside but not in the colder temperature overnight as they will always be in the warmth.

I'll have another post on how to successfully transplant seedlings in the next couple of weeks but if you have any questions, feel free to get in touch!

Other garden posts you might like:

How to Grow Strawberries

Growing Strawberries in Raised Beds

Our 2018 Summer Garden Plan

How to Start Seedlings Indoors

How to Start A Patio Herb Garden

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