How to harden off your plants before putting them outdoors

If you have grown plants indoors or using heat and grow lights in order to get a jump start on the season. Then the next step before you transplant them out into your garden is to harden them off. It sounds like a traumatic, complicated thing, but really it comes down to this. Little and often.

So let me explain in simple terms, how to make sure you can transplant your little plants and seedlings without damaging them or worse, killing them. If I asked you what you might worry about when transplanting your little plants to your garden, I suspect very quickly you’d say temperature. And you would be right. Temperature is a major factor in damaging or killing plants that are put out into the garden, but there are actually other things to consider too, sunlight being a massive factor in plant damage and of course wind and weather.

Why sunlight is important

Firstly let’s talk about sunlight.
We all know how dangerous sunlight can be for our skin, and how too much sun can burn us and cause permanent damage. Well, it is exactly the same for your plants. Right now I know you are thinking, but Eli, plants are outdoors all the time, how can sunlight damage them?

Well, that’s true, in normal circumstances, sunlight wouldn’t damage plants but that’s because plants have a waxy coating on their leave to protect them. It’s called a cuticle and it repels water, reduces dehydration and it filters UV light. Therefore providing an awful lot of protection for a baby plant. But, this is something plants develop as needed and indoor-grown plants haven’t had the chance to develop it yet, so they are particularly susceptible to sunlight. So we need to help our little plants develop this protective layer before we throw them out to the harsh reality of life outdoors.

How weather can impact our plants

Weather is a big area to cover, and some of it is obvious, like temperature. But other things may not be like wind and rain.

Again our little indoor plants have grown in a sheltered environment, so other than maybe a fan you have used to encourage airflow, they haven’t had to deal with wind. Even a breeze. This means they’ve yet to develop that strong stem and root structure. So with careful hardening off, we’ll help them develop that.

Rain can also be problematic for little plants in pots. There isn’t a lot of soil to disperse any heavy rainfall allowing those little roots to be soaked and left standing in water. Long term this isn’t good for any plant but can quickly develop into a problem with plants in pots.

Lastly, the temperature is obviously a concern. We don’t want to put our plants out into the garden if it’s colder than the temperature they need, but we also need to be aware that those little plants have got used to the conditions we have grown them in, so a sudden change to that temperature can shock them, cause serious stress and potentially kill them. So again, we need to let them get used to this new environment in a way that doesn’t cause them stress.

How to harden off your plants

Firstly, let me reassure you that it’s actually a really simple process to follow to harden off your plants and get them ready to go outdoors. Or indeed to any new environment. As I said earlier it’s about little and often. We want to allow our plants to gradually get used to all these changes they will face, sunlight, wind, temperature and other changes. We do this by starting off with putting out plants out into the new environment for a short period of time, in a protected spot and gradually increasing that time over a period of a week to two weeks. I do it like this.

Once it is safe to plant my seedlings and young plants out into the garden, in other words, once the last frosts have passed and the temperature is stable and safe for them, I choose a cloudy day and put my plants out early in the morning in a spot where they will be sheltered from wind and sun and rain. I don’t leave them out long on that first day. Maybe only half an hour to an hour.

Each day I do this and I gradually increase the length of time that my plants are out. This allows them to get used to all those strange new factors in the garden, and build their strength and resistance without shocking them or causing them stress.

My aim is that by the end of that first week, my plants will be ready to be moved away from that sheltered spot and to experience some time in the garden where they will experience the fluctuations in sunlight, temperature and wind without the added support of the shelter.

Over the next week, you can watch your plants and be alert for any signs that they are struggling. IF you see that maybe they are, you can simple move them back into the sheltered spot and give them a little more time. If however your plants look like they are coping well, then you can start to think about planting them out permanently into the garden.