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How To Harden Off Vegetable Plants & Flowers – Get Your Plants Ready For The Outdoors!

One of the most important things you can do this spring to get your vegetable and flower plants off to a great start is to harden your transplants off before planting them permanently outdoors.

Whether you raise your own plants from seed indoors, or purchase transplants from a local nursery or greenhouse, preparing them properly for life outdoors is crucial for both a plant’s short and long term health.

When done correctly, it sets the stage for plants to take hold, establish, and grow fast. But when plants are not properly prepared before planting – the shock and stress can damage, injure, stunt – or even kill off young plants early on.

harden off vegetable plants
Young seedlings and transplants need to be prepared for life outdoors before going in the ground. If they aren’t, trouble can loom.

The topic of hardening off often stirs up a bit of confusion for gardeners. Many are unsure of what the hardening process really is. Meanwhile, others are not sure just exactly how to do it. Especially without causing harm to their plants in the process.

Hopefully, today’s article will shed light on all of the questions and concerns. And, in the process, help you get your plants ready for an incredible year of growth and beauty.

With that in mind, here is an in-depth look at exactly what the hardening off process is, and how to do it correctly to have your plants ready for planting day!

What Does It Mean To Harden Off Vegetable Plants & Flowers

In a nutshell, hardening off is the process of toughening up young, tender plants for life outdoors. Whether raised in the house or in a greenhouse, tender seedlings are unprepared for the perils Mother Nature can bring.

Inside in a controlled environment, there is no such thing as a strong wind or heavy rain to whip and damage tender foliage. Nor are there any worries of intense sunlight or blazing daytime temperatures.

how to harden off flower plants
When growing indoors, this young tomato plant never had to worry about a strong thunderstorm whipping its stems, or a hard downpour pounding its leaves. Hardening off helps young plants to prepare for what they will face outdoors.

If those weren’t enough to contend with, there is the occasional cold or even frigid night that springtime can bring. Chilling temperatures that can stunt and damage plants, or even kill them off with a hard frost or freeze.

If you take a sheltered seedling and force it into those harsh conditions all at once, it is simply too much for it to handle. A strong wind will whip over an unprepared tomato plant and kill it in an instant. As can a hard rain that can knock over a tiny flower transplant that is outside for the first time.

But hardening off these plants slowly over the course of a week or two allows tender transplants time to slowly adjust, prepare and strengthen. And when they are planted outdoors – they are ready to grow!

How To Harden Off Vegetable Plants And Flower Seedlings

How you harden off your plants will depend on whether you grew your own transplants from seed, or purchased them from a nursery or greenhouse. Let’s first cover preparing home grown transplants for life outdoors.

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For those who grow their own seedlings indoors, the hardening-off process should begin about three weeks before planting day. By this point, your plants should be far enough along (around 4 weeks old) to start getting ready. (See: How To Know When To Start Seeds Indoors)

Begin by setting plants outside on days that are both warmer (55° F+) and less windy. Select a protected area such as a porch or patio and give them a few hours outside.

For the first day, allow them to get a bit of sunlight, but just a few hours at the most. Continue to do this on nice days, allowing the plants a bit more time out with each passing day.

Within a week, if the weather allows, move your plants so they can receive even more light. Always, and this is very important, make sure to provide them with some protection against strong winds.

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

hardening off transplants
Our tomato plants hardening off outdoors, with the added protection of a wooden border wall to help keep them safe from strong winds.

The air, sunlight and protected breezes helps plants to slowly toughen up. It is amazing to see the changes that will take place in your plants in just a few days from being outdoors. Most notably, a complete difference in your plant’s strength and growth!

Continuing The Process – How To Harden Off Vegetable Plants & Flowers

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 temperatures are going to stay above 45 degrees, you can begin to keep them out around the clock.

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

Purchased Vegetable & Flower Transplants – Hardening Off Plants

So what about plants that you pick up at your local nursery, greenhouse or big-box store? Believe it or not, they can use a bit of hardening off too in order to prepare for life outdoors.

Although these plants are often larger than home-grown transplants, many have still not spent a single minute outdoors. Much as with your home grown seedlings, allow the plants a few days outdoors in a semi-protected space.

petunias outdoors
Store bought plants, whether vegetables or flowers, can still benefit from a bit of hardening off before direct planting.

In the evening, bring them into a protected garage, barn or indoor space for a few nights as well. Keep them from strong winds and heavy rains as well to avoid damage. Once they have a few days under their belt, you can let them to stay outside around the clock unless a frost or storm is in the forecast.

Because the plants are bigger, a week or so of hardening off is usually more than enough time to get store bought plants ready to go. If plants happen to be on the smallish side, it is best to give them an additional week.

An Exception To The Rule

There is an exception to the rule of hardening off plants from a store. If you are purchasing late in late spring or from nurseries who have already placed their plants outdoors – simply buy and plant!

If they have been outdoors, they have already been hardened to the weather extremes. In addition, the later you get into spring, the warmer both the soil and weather will be, and there is not the same danger early spring can bring to plants.

Here is to preparing your vegetable and flower plants for life outdoors – and to a great growing season this year! Happy Gardening, Jim and Mary.

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