Will I need to harden off plants?

We’ve been asked this question a few times recently, so thought we’d put together an article. The short answer is no, because we grow our plants in unheated polytunnels, and then they move to our cooler packhouse ahead of being packed and shipped, so they are quite hardy. However, hardening off the plants, or at least making the transition to the outside world a little gentler, isn’t a bad idea.

What is ‘hardening off?’

If you’re new to growing and haven’t come across this term before, hardening off is a simple process of getting young plants that have been raised under cover in polytunnels/greenhouses gradually acclimatised to the outdoors over a few days. This is normally done by moving young plants outside during the daytime, and then bringing them back under cover over night.

Do all plants need to be hardened off?

No. Many, like brassicas, leeks and roots, are pretty hardy anyway and you can plant them straight out in spring without worrying too much (unless of course it is very frosty!)

The ones you need to watch out for are these:

  • Tomatoes, Aubergine, Chillies & Peppers
  • Cucumbers, Courgettes, Squash & Pumpkins
  • Sweetcorn, Beans & Peas

How is it done?

With small plants that you get from a garden centre, that are in plastic pots, this is easy as you can just put them all on a tray and move them around in their pots. For our plug plants, most of which are bare-rooted and not in pots, it is not quite so simple, but we have a few ideas for you.

Option 1 – loosely plant in a tray of compost

You’ll need a tray that is around 7-10 cm deep. After soaking the root balls in water, you can stand the plugs in the tray and then sprinkle some compost around the roots, loosely, until all the root balls are covered. Then, simply move the tray outdoors during the day and back under cover at dusk for the first week or two before planting them in their final positions. When you do plant them out, make sure it is a nice gentle day with no chilly winds or frosts on the forecast. The plants will be easy to pull out of the trays as they won’t have had time to establish their roots.

Option 2 – plant out and cover with polythene sheet, fleece or mini cloche at night

You can plant out straight away if you need to, and simply cover the vulnerable plants with a sheet of polythene or cloches at night time, and exposing the plants during the day. Leave them covered too on cold days if there is a particularly harsh wind.

Option 3 – use an open ended cloche tunnel

This is a good option if you are planting out in rows – a simple cloche tunnel will protect the plants, but you can leave the ends open and just leave the tunnel in place until, say, mid-May when all risk of frost and all cold winds have passed through. Then remove the cloche and leave the plants to it.

Option 4 – request that we delay your plants

You’ll receive an email notification with delivery details a few days before your plants are shipped. If it is still very cold in your area, you can ask us to delay the delivery for a couple of weeks. This is a good option if you don’t have the ability to do any of the above, or if you live in a particularly cold part of the country and don’t want to take the risk of planting out too early.