9 steps to prepare your polytunnel for winter

POT'S GROWING ON? 10/11/23

If you have a polytunnel or unheated greenhouse, it’s time to show some love to get the most out of them over winter and next spring.

1) Clean the outside to let more light in

Photos by Christopher Lyon Anderson

After a long season of weather, the outside of your polytunnel or greenhouse can look pretty sad at this time of year, covered in autumn leaves and algae. This can lower light levels inside more than you might think, especially in the shorter, duller days of winter. Thankfully, it’s easy to give it a good wipe with a cloth or sponge and some water. I’m going to invest in a long handled sponge to reach the top. I don’t think you really need to use soap but you can if you want, I’d just recommend environmentally friendly soap to not contaminate soil where you are growing food. Though for me, water is fine.

2) Remove summer’s spent crops and add to compost pile

If you haven’t already, start by removing all those old tomato, chilli and aubergine plants, and anything else you might have. Last year I saved and reused the twine to grow the plants up but I’m cutting it off this year as it’s slowly weakened, to be replaced next summer. I pop them on the compost heap, saving any last minute tomatoes and other crops!

3) Hoe the ground

Unwanted seedlings may have snuck in beneath your crops and particularly around the edges. Hoe and hand pull these out at the roots being careful around the edge not to damage the cover.

4) Add a layer of sustainable compost

I’m lucky to be adding homemade compost, when this runs short I order local sustainable compost which is made from decomposed plant material, just like homemade. This recycles waste plant material and doesn’t exploit natural habitats like peat bogs. I’m giving the ground a really good thick layer this year (about 5cm) to boost its organic matter content, mainly for structure as the soil is looking thin and powdery, though it will also add nutrients.

5) Rake it over evenly

You can see our homemade compost is quite twiggy, I’m not really worried about this, the larger pieces help with the structure of the soil and the twigs are at least two years decomposted. They’re very broken down and easily to snap up into smaller bits. Any really large bits can be removed. Around the edges I will likely add a run of cardboard from deliveries about 40cm wide to help prevent weeds growing under the side. This compost will be good for the winter salads going in, but should also be enough for the tomato plants next spring.

6) Sow overwintering peas and broadbeans

I’ve sown pea ‘Meteor’ and broadbean ‘Aquadulce Claudia’. Down south on my London allotment I used to sow these outside without cover and they grew happily. Up here on our more exposed plot, I am going to grow them inside the polytunnel this winter. Over the last few winters they have rotted or struggled with the excess winter wet and cold. I could try covering them on the allotment with horticultural fleece but I have space in the polytunnel and tomatoes don’t get planted until May when they should have cropped so I’m going to grow some here.

7) Cover legume seeds with mesh to stop mice and rats

I did actually plant a row of peas on the allotment last month but within a day I saw they had been dug up and eaten by something almost certainly a mouse, vole or rat. They must have super scent, or were watching me put them in! In the polytunnel I can prevent this by covering with mesh. It’s best to use 1cm mesh as that’s small enough to stop mice. Here I’ve used two mesh garden shelves overlapped to make the gaps finer. I will remove them when the seedlings germinate. When the roots show at the bottom of the pots I’ll plant them into a corner of the polytunnel.

8) Prepare winter salads

I sowed all of my winter salads back in late-August and early-September so it’s a bit late to do this now really, though I do plan to sow a row of mustard direct into the ground. That seemed to work well last year as they still germinated, if a bit slowly. I’ve sown mustard, lettuce, beetroot leaf, mizuna, mibuna, lamb’s lettuce and spinach. I always sow everything into regular peat free compost, I don’t bother with seed compost. These will fill the polytunnel when I plant them out in a week or so. I fertilise with half strength liquid seaweed every so often, usually when there is a milder sunny spell, being careful not to overwater, which can lead to roots rotting.

9) Water crops from time to time

It may be wet outside but remember it doesn’t rain in a polytunnel or greenhouse! You don’t need to water as often because it is colder, the water won’t evaporate. Just keep an eye on how moist or dry the soil is about 10cm below the surface.

For information, I was given this polytunnel as a gift by Premiere Polytunnel’s two years ago for a no-obligation assessment of its features (you can read that here). I only mention this again now because to their credit, the polytunnel is still going strong and I’m impressed with it, so credit where credit is due. This isn’t an ad and they haven’t asked me to mention them again, but I want to be transparent with you my dear reader and fair to the company.

Are you growing any crops outside or undercover this winter? Please share what you are up to in the comments below.

p.s. if you happen to own a copy of my sustainable gardening book A Greener Life and have a spare moment, it would be brilliant if you could leave a review of it on Amazon here - it’s annoying that reviews on there matter but these days they really do make a big difference to writers 💚