Skip to Content

How To Harden Off Seedlings & Transplants Before Planting Outdoors

What is the best way to harden off tender young seedlings and transplants before planting them outdoors? And perhaps even more importantly, why is the practice so important to a plant’s long-term success and well being?

If there is one spring gardening topic that causes a fair amount of confusion for gardeners, it is the subject of hardening off plants. In a nutshell, hardening off is the process of preparing young plants for life outdoors.

Although the task is not particularly difficult or time consuming to do, it does play a major role in just how well your plants adapt and grow once they go in the ground. In fact, in some cases, hardening off correctly before planting can actually mean the difference between life and death for a plant!

harden off seedlings
Once transplants go in the ground, life gets tough quickly. If not prepared properly for life outdoors, tender young plants can struggle to grow and even survive.

One thing is for sure, whether you grow your own vegetable and flowers from seed – or purchase transplants from a local nursery, greenhouse or big-box store, they need to toughen up a bit before they can be planted outside.

Preparing Young Plants For Outdoor Life – How To Harden Off Seedlings & Transplants

The first six to ten weeks of a seedling’s life is extremely easy no matter where they grow. Whether inside of your home or in a commercial greenhouse, young plants are completely pampered and sheltered from the many dangers of growing outdoors. (See: How To Know When To Start Seeds Indoors)

There are no heavy winds to topple them over. No pounding rains that might smash their small leaves and stems to the ground. Even more importantly, there are no huge swings in temperatures.

Indoors, seedlings don’t have to deal with scorching afternoon sun or chilly nights. And of course, if cared for properly, they get plenty of water when they need it too. But all of those cozy conditions change drastically on transplanting day. And if plants are not ready for harsh conditions, they can suffer serious damage quickly.

wind damaged tomato plant - why hardening off matters
This young tomato plant is suffering from wind damage. If plants are not properly prepared for outdoor life, they can injure easily.

That is exactly why hardening off your transplants is so important. Not just for plants you are growing yourself from seed, but for many of the plants you purchase from a store. The good news is – it’s easy to do. And it can help to get your plants off to their best start ever!

How To Harden Off Seedlings & Transplants

Young plants need time to adjust to the sunlight, wind and temperature swings that outdoor life brings. If you take a seedling or transplant directly from inside and plant it in your garden or flowerbed, it most likely will fail quickly. It simply won’t be able to handle the stress of the quick transition.

But by slowly giving it time to adjust to outdoor life, and protecting it a bit as you do, that very same plant will begin to strengthen. Even better, in a fairly short amount of time, it will then be able to withstand all that nature can bring.

How much adjustment time your plants will need before planting day depends on whether you have raised your own seedlings or purchased them from a greenhouse. On average, home-raised plants need two to three weeks of hardening off, while nursery plants usually need a few days to a week at most.

Why the difference? Plants raised from seed in a home tend to be less developed than store bought plants. The main reason is commercial growers start their seeds extremely early. Because of this, plants have had longer to grow and mature.

Listen In To Our Podcast On How To Harden Off Plants With Ease!

In addition, commercial greenhouses have controlled lighting, watering and fertilizing. They also often place large fans on the plants as they grow to help them strengthen even more.

All of these advantages help greenhouse-raised plants to be more developed early on. But with a little extra prep on your home grown plants, you can have them equally prepared to take on the outdoor growing season with ease.

How To Harden Off Home Raised Seedlings & Transplants

The process of hardening off seedlings and transplants at home all begins by setting your plants outside for a few hours each day during warm afternoons. It is best to try to do this (if the weather allows) about two to three weeks before your anticipated planting day.

Whatever you do, on those first few days, don’t just sit them directly out in the hot sun or in a wide open space. It is extremely important for the first week to ten days to provide them with a bit of protection.

Porches are perfect. Covered and protected decks and patios are as well. You can even open up the garage door and keep them near the edge to give them a little sun. This initial protection helps them get acclimated to the outdoor elements slowly.

harden off transplants for planting day
Hardening off your plants prior to planting will have them well prepared for strong winds, hot sun and more. It will also lessen the time it takes them to get over the shock of transplanting.

It’s very crucial at this point to protect them from any strong winds. Wind can whip tiny stems over. It can also whip the foliage, injuring leaves or even killing plants in the process. If need be, place a few boards around the edges of your plants to protect them from direct wind.

As each day progresses, allow your plants to get more sun and more exposure to the elements. With a week or so to go before planting day, only move your plants indoors if the temperatures dip towards a frost, or brisk winds or heavy rains are forecast.

A few days before your planting day, leave plants outside in the full sun and light. At this point, they are hardened off and ready for planting!

The Hardening Off Process For Store Bought Transplants & Seedlings

So what about preparing store-bought plants for planting outdoors? How long these plants need all comes down to how large they are, and at what point of the growing season you will be planting them.

As covered above in the article, most nursery raised plants are already further along in the growing process. Many large flat of plants at nurseries have already spent a bit of time outdoors on racks or shelves. For these more mature plants, hardening off is really not necessary.

Many flowers and vegetable plants in nurseries or plant stores have already spent time outdoors. For these plants, hardening off is not necessary.

But if plants are on the smaller side, or have been inside exclusively at the nursery, allowing them to have a bit of protected time outdoors before planting can reduce the chance for transplant shock. A few days outside is usually more than enough to do the job.

Finally, if you are planting late in the spring or even into early summer when temperatures have already warmed permanently, there is no need for hardening at all. Here is to hardening off your flower and vegetable seedlings – and to getting the most from your plants this year!

Follow Our Facebook Page For Great Gardening Tips And Advice! This Is My Garden Facebook Page

This Is My Garden is a garden website created by gardeners, for gardeners. Jim and Mary Competti have been writing gardening, DIY and recipe articles and books and speaking for over 15 years from their 46 acre Ohio farm. They publish three articles every week, 52 weeks a year. Sign up today to follow via email, or follow along!