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Polytunnels: preparing for winter

Winter should be a time when gardeners can sit back and relax, and browse seed catalogues in anticipation of the next season. But before you decide to take it easy, make sure you’ve finished preparing the polytunnel for winter, so the plants inside will be safe! If you haven’t already got things ready, now’s the time. Most of the UK will experience its first frost during October, so don’t leave it until it’s too late.

Wash the cover

Light levels are much lower in winter, so winter and hungry gap plants need all the help they can get.

For a smaller tunnel up to 10ft wide, one person can do the job with a soft broom and a hose. Wet the cover, then use the broom to carefully and gently brush dirt, bird poo and green algae loose from the surface, then rinse it away. This is best done on a warm day, as warmth will make the cover less brittle. The last thing you need at this time of year is a big tear to fix!

If your polytunnel is wider than 10ft you need to ‘floss’ it instead, as a broom can’t reach the very top. For this, you’ll need two people, an old sheet and two lengths of soft rope. Roll up the sheet into a long bundle and soak it in a bucket of warm soapy water. Tie a piece of rope to each end of it (or run a longer piece through the middle) then sling it over the top of the tunnel – and get flossing!

Article – How to Clean a Polytunnel

Check for tears and holes

These can be fixed with polytunnel repair tape, and it’s always a good idea to have some on hand. You never know when you might poke a bamboo pole through the cover, or worse, and if you leave it untended the first storm will turn it into a major tear. You can buy repair tape from the supplier of your polytunnel.

Got mice?

If rodents have moved in to the tunnel during warmer weather, now is your best chance to get rid of them as during the winter they’ll start doing serious damage to your crops, eating almost everything that you planned to pick for yourself. Overwintering beetroot, cabbage, carrots and even lettuce will be gradually gnawed away, and potted plants, brought into what you thought was a protected area, will suffer too: for instance, if you have an olive or bay tree they’ll eat the bark and kill it. Rooted sweet potato plants will simply vanish overnight. However, don’t forget that they’re just living beings who get hungry – just like us. Don’t kill them, as they really don’t deserve it, so use a ‘live’ trap that can catch up to 10 mice in a single night. For voles, more difficult to catch and more vulnerable when caught, you’ll need something a little more convincing. If you’ve got voles in your polytunnel, read this.

Clean up

Grass along the cover edges can harbour slugs, woodlice and others who will relish the chance to set up house in your polytunnel over winter. They’re bad enough at the best of times, but in winter when your plants will grow only very slowly, any damage they cause sets everything back far more. Tidy up everywhere you can so that they’re not tempted, and relocate any you find in the process.

Winter planting

While it’s too late to plant many seeds, it’s not too late for all of them. If you’re planning on an early spring crop of broad beans, October is a great time to get them going, and the same applies to overwintering peas – the ‘round’ seed type. The ‘wrinkled’ seed varieties are not winter hardy and won’t make it through.

Other crops such as spring onions, turnips and cilantro can be planted any time of year, so if you have some space pop a few seeds in and see what happens.

Elephant garlic

This is a great winter crop, and planting it in October or even early November means it grows through the cold, which helps it to develop a strong root system. It suffers from very few pests or diseases, is quite hardy, stores well, is delicious to eat and you’ll probably find your local deli or restaurant will be very interested in exchanging your extras for cash. Best of all, it’s out of the ground in June, just in time to prep the bed for big summer plants like courgettes, cucumbers and melons. For more detail on what to do for a great Elephant Garlic crop, read our Garlic and Elephant Garlic article.

Get your fleece cloches ready

A fleece cloche helps to ensure the survival of many crops such as lettuce pak choi by providing an additional layer of protection from frost.

fleece cloche, image

A fleece cloche can help keep tender plants warm and cosy through the winter

If you leave it too long, just one severe frost will kill plants off and then it’s too late. Don’t be caught out! Put a cloche in place before the end of the month; you may not need it until January, and you might not need it at all – but if it’s there, your plants are safe. Build it so that on clear, sunny days you can quickly and easily pull the fleece back and let your plants benefit from the additional light, but don’t forget to pull it back down again at least an hour before the sun sets. You can buy fleece here from Harrods Horticultural, or a complete, ready-made cloche.

Don’t forget about watering and ventilation!

Surface moisture dries out much slower in winter, and you may think that just because the earth looks damp, it is. However, further down it might be a different story. A water sensor is even more useful in the winter than in the summer and will tell you whether your soil is damp, wet, or dry. They don’t use batteries and there are no moving parts, so there’s very little that can go wrong. Push the sensor rod into the ground at several places around the plants so that you get more than just a single reading. They are especially useful for potted plants.

Ventilation will help to keep mould and excess condensation away throughout the year, even in winter. Whenever you can, open the tunnel doors for the day. If it’s very windy, just open them a little at the sheltered end. The only time you shouldn’t leave them open is if it’s frozen and forecast to stay that way. In that case open both ends for a few minutes as early as possible, to let the trapped cold air out.

Then, once you’re done, it’s definitely time to relax! Don’t forget that seed catalogue…

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4 Responses to “Polytunnels: preparing for winter”

  1. wendy reynolds says:

    oh help mice what can i do to get rid off, they have their nests in the plants

    • Andy McKee says:

      Put a high-sided bin under your staging, and balance a loo roll on the staging edge with a smear of peanut butter on the outside end. Mousie will fall in, but make sure you check the bins frequently so the mouse isn’t trapped for too long. Release somewhere with good cover at least a mile away.

      And next year, thin out plants a bit more to make it a less attractive environment. Also, don’t store anything in the tunnel over winter as it just provides food and nesting material for the little blighters.

    • Mark Gatter says:

      Hi Wendy,

      They might not be mice: they could be voles in which case the loo roll solution won’t work. You’ll need a proper ‘Longworth’ vole trap – see our article:
      http://www.farminmypocket.co.uk/blog/vole-damage-in-the-tunnel
      for advice – and good luck! Incidentally, voles are REALLY delicate and you’ll need to check the trap twice a day – otherwise you may have dead voles. Make sure the trap contains fine straw, or grass for insulation, and something to eat – carrots are ideal.

  2. Thom Wills says:

    Very useful – Thanks for all this great info. This is my first winter growing veggies in my tunnel. We also help the growing season for gardeners big and small.

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