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Hardening off your plants – it’s a bit like lifting lockdown

By now I think most of us have at least some little baby plants and a whole lot of desire to get them out into the garden. So I feel it’s only right for me to jump up on that soapbox, with a little help from a small step, and shout, NO! Don’t do it!

Let me explain, if you grow plants indoors or in a greenhouse etc with the intention of at some point planting them in your lovely garden, you need to be gentle. If you just put those little babies straight out there into the garden, you will shock them and in the worst case, you may actually kill them. Now none of us wants that, so let’s just have a wee chat about how you can avoid this total disaster. It’s called hardening off.

Firstly let me assure you that this isn’t a bit complicated gardening secret thing, it’s actually dead simple and just about having a tiny bit of patience. So let me explain the whole thing, it’s about little and often. Think of it like this. Your little plants have been all warm and safe on the window sill, in the greenhouse etc. Now that means they’ve had protection from two things, the weather and the sunlight. In a greenhouse, there is a degree of UV protection and a degree of sunlight is blocked. In the house on your window sill a similar thing happens, the sunlight is restricted a little. All this means that those little seedlings haven’t yet built up their protection from harsh, direct sunlight. Yup, believe it or not, plants grow a coating on their leaves to protect them from the sun, but our little pampered babies haven’t had to do that yet, so we are going to let them build this up, gently.

Also, they have been protected from the weather, or at the very least from the worst of it. So we don’t want to just throw them out to the cold, rain and wind. Or worse, if you live in Scotland, this week, the frost and snow. Instead, we help them to strengthen up a little and get used to things.

So how do we do all of this? Well in stages. So we start off very carefully and only expose the plants for short periods, then over time we build up how long they spend in the new environment. Think of it like this – regardless of how you start off and how you finish (window ledge to garden, window ledge to an unheated greenhouse, greenhouse to garden), every switch from one environment into another means a short period of adjustment. So let’s do this as an example of me moving plants from my greenhouse to the garden. And just for fun, let’s throw in a tenuous lockdown analogy.

Stage 1 or Tier 4

So our little baby and very tender and delicate plants start off in Tier 4 – where they can’t leave the house (greenhouse). They stay indoors waiting on those first signs that the weather is changing and that the frosts will soon be gone. On this note, it is always good to know roughly when your last frost dates are in your garden. This will help you decide when to start hardening off your plants and reduce the risk of unexpected frost causing problems.

Stage 2 or Tier 3

There is light at the end of the tunnel, the restrictions are easing, a little. It’s a few weeks until our last frost date and during the day the temperatures are up in double figures, just. So now our little plants are allowed outdoors for a short spell each day, say a couple of hours to start with. You still want to be careful though, avoid direct, harsh sun and areas where they might get battered by the wind. After all, we are only at the very beginning of these little darlings getting out, it’s going to take some adjustment. I usually do this for about a week lengthening the time they are outdoors each day by an hour or so.

Stage 3 or Tier 2

So we are now allowing our little darlings a bit more freedom, we now know they can cope with a few hours each day of being outdoors, so now we are going to move to leaving them outdoors all day. Oh, the heady excitement. Now, remember, we’re still in plant lockdown here, so they aren’t allowed to go visiting their friends at the other side of the garden yet, gotta stick to their bubble. But they are out there, loving the sunlight on their little leaves and the wind in their fuzzy trichomes.

Stage 4 or Tier 1

This is the very last and most exciting stage of your little plant’s journey, you now know they can cope with being outdoors all day, but this stage may just be the scariest. We are going to leave them out through the night as well. This is the scariest because the temperature during the night will be much colder. Now you can see why we don’t start this process until we know that the risk of frosts has passed. We are now acclimatising the little plants to the outdoors and all the fluctuations before we take them out of their pots and plant them directly into the ground (or garden containers). Again I will give this stage the best part of a week, just to be certain.

HURRAH! Lockdown has been lifted, it’s time to get the little plants into their forever homes. There’s no “I’ve been vaccinated” sticker to sport proudly but your little plants have made it through lockdown and come out the other side unscathed, they can now go meet all their little garden friends and enjoy a full and happy social life.

raised bed with flowers and cloches

Just on a note, you may add other stages into this to suit your garden and your equipment, for instance, you may use cloches and cold frames to help protect plants while you harden them off, but the basics of the process are just about exposing your plants a little each time and not rushing things.

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