So just exactly what does it mean to harden off vegetable plants and flower seedlings before planting outdoors?

And, why is it so important?

Those two questions are often asked by gardeners every spring. And with good reason.

 how to harden off vegetable plants
A young tomato plant grows indoors, awaiting life in the garden.

Whether raising plants from seed at home, or purchasing transplants from a nursery or greenhouse, the process of hardening off is a big key to a plants short and long term health and success.

Why You Need To Harden Off Vegetable Plants & Flowers

In a nutshell, hardening off is the process of toughening up young, tender plants for life outdoors vs. Mother Nature.

Whether raised in nurseries or at home, tender seedlings are simply unprepared for life outdoors.

Inside in a controlled environment, there is no such thing as a strong wind or heavy rain to whip and damage tender foliage.

harden off vegetable plants and flowers
Both flowers and vegetables need time to adjust from their cozy life indoors before being planted outside.

Nor are there any worries of intense sunlight or blazing daytime temperatures to quickly dry out plants. Or even a cold night that might bring a damaging or deadly frost.

But hardening off plants allows tender transplants time to slowly adjust and prepare for all of those harsh outdoor conditions.

And in the process, keep them safe from injury, transplant shock, or even complete failure.

The Process – How To Harden Off Vegetable Plants And Flower Seedlings

For those who grow their own seedlings indoors at home, the hardening-off process should begin about three weeks before planting day.

Begin by setting plants outside on warm days (around 55 degrees or above) in a protected area.

We use 1 x 12″ boards screwed together and placed on the ground around our flats. It keeps the wind from knocking them over, but still allows them plenty of sunlight and air.

placing plants outdoors
While hardening off, we use 1 x 12″ wooden boards placed around our plants to protect them from harsh winds.

Porches and patios are also ideal for this task.

It gives plants their first taste of outdoor living, while still having a bit of protection from full sun or heavy winds.

For the first week or so, bring plants inside at night to keep them safe from cool or freezing temperatures.

As spring continues to warm the air, allow transplants more and more time outdoors. In fact, as long as night time temps stay above 45 degrees, keep them out around the clock.

vegetable transplants
Seedlings indoors have it easy. But outdoors, a whole new world awaits!

As planting day approaches, plants should be spending nearly all of their time outdoors. Only bring indoors if a frost, high winds, or a heavy storm is in the forecast.

By following this process, your plants will be more than ready to handle the shock of transplanting.

What About Nursery & Greenhouse Plants?

Store purchased plants are usually a bit larger and more robust than those grown at home.

But even so, most have still spent all of their life protected indoors.

planting the garden
After hardening off, plants are ready for Mother Nature.

And a bit of hardening off for a few days or a week can go a long way towards helping them to adjust to outdoor life.

Start by sitting out newly purchased plants outside in a semi-protected area

Keep them from strong winds and heavy rains, but allow them to stay outside around the clock unless a frost or storm is in the forecast.

These plants are usually much larger, so a week or so is usually more than enough time to harden them off.

Now it’s all about getting those plants off and running! (See : The Ultimate Planting Day Guide – How To Start Your Plants Off Right In The Garden!)

A Few Exceptions To The Rule

There are a few exceptions where you do not need to harden off vegetable plants and flowers.

If you are purchasing late in late spring, or from nurseries who have already placed their plants outdoors – simply buy and plant!

Happy Spring and Happy Gardening! Jim and Mary

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How & Why To Harden Off Vegetable Plants & Flowers Before Planting