How to Harden off Plants in Nurseries




What is hardening off plants and why the heck do you have to do it?

When you go to a nursery, all those young plants are already outside and ready to go into the ground…why can’t you do that with seedlings you’ve raised yourself at home?

It has surprised me that there’s quite a bit more work that goes into raising seedlings than I ever would have imagined!

While some seeds can be plopped into the ground haphazardly with decent outcomes, some seeds must be grown in a more controlled environment, and must be handled quite carefully if they’re going to survive and even flourish as adult plants.

I recently purchased some plants at a plant sale held by the horticulture club at my university. I bought several vegetables, annuals and perennials.

I was told that these plants hadn’t been “hardening off” yet, and if I wanted to make sure they survived, I needed to do that over the next week or two before putting them in the ground.


Well, I suppose the discounted price I paid for these babies makes it worth the effort. In addition, it taught me a thing or two about how to handle this “hardening off plants” process.

So what is “hardening off plants” and how do you do it?

Plants that are germinated and raised in greenhouses are raised in a very cozy environment. They are pampered and catered to in order to produce good healthy plants to go out to the public.

Unfortunately, this cozy environment means that these babies have been just a wee bit spoiled, and must be prepared to enter the cruel, harsh world that exists in your garden.

I know, I know…you probably don’t think of your garden as being “cruel” or “harsh”. But to a young seedling that hasn’t experienced

  • Direct sunlight (generally greenhouses have filtered sunlight), or
  • Winds of any kind (there isn’t any wind in a greenhouse), or
  • Cold evenings (greenhouses strive to maintain consistently warm temperatures for young plants), or even
  • Moderate rainfall (plants have been delicately ‘misted’ up until this point).

Your garden can indeed be a cruel, harsh place, and plants that have not been hardened off may quickly perish if moved directly from the greenhouse to the outside elements.

Hardening off plants takes a good 1-2 weeks to accomplish the task.

What you’re trying to accomplish during this time is exposing the young plants to the outdoor elements a little bit at a time, so they can survive and thrive in the garden.

You will expose them to:

  1. sun
  2. wind
  3. water
  4. temperature

so that they can be safely planted in the ground.

Start the first day or two by placing them outside in a relatively protected location for several hours. The first day I had mine outside for about 4 hours, and the second day they were outside for about 6-8 hours.

hardening-off plants

I placed them right outside the patio door. This way they got direct sunlight for half the day, and were somewhat protected from the wind. At night I brought them into the house.

It’s important to pay attention to the temperature as they should not be outside when it is close to freezing. Freezing temps will kill off young seedlings faster than you can say, “Adios!”

I did keep the plants watered well for the first couple of days, but then also started cutting back a bit on the water. You don’t want to dry them out, but you do want them to get used to not being slightly moist all the time, like they were in the greenhouse.

The reality is that plants get lots of water from time to time, and have to go without at times.

You’re encouraging the young plants to become adult plants one step at a time by artificially creating a “real life experience”.

Don’t be overly exuberant if you notice the temps warming up while you’re hardening off plants. You are getting them used to the temperature at every end of the spectrum…chilly temps as well as hot temps.

Hot temps and a full day in the sun can kill young seedlings as easily as cold temps and high winds all day if they’re not used to it.

I moved my plants in and out of my house the first couple of days they were with me because we had freezing temps at night, and I didn’t want to chance to have them in the garage.

As they toughened up a bit, I moved them in and out of the garage the second week, leaving them out at night by the end of the second week.

If you’ve got a number of flats that you’re working with, it may be easier to place them on a wagon so you can easily move them in and out of their protected area.

Usually, the garage is a safe place to keep them at night unless the temps go too low.

After 1-2 weeks of this back and forth, you should have sufficiently hardened off your plants and can safely move them to their new garden homes!

I'm your average, everyday kind of gardener; I learned from trial and error and reading magazines; gardening for many years. ....Since I was about 23 and a first-time homeowner. I’m also a working mom with a wonderful husband. We keep busy with our yard and garden, and also the visits from our 6 grown children and other family and friends that we entertain on the weekends.

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