Polytunnels, advice on buying

BUYING A POLYTUNNEL

Some tips to help you make a good choice

Polytunnels are wonderful structures and good value compared to greenhouses. Once erected they will be there for several years, so check out my tips before buying.

I have used polytunnels since 1983 when I bought 3 of 18×55 feet (5.5x17m) and they served me well except that their 1in/2.5cm tubes were too thin for my exposed site. In a gale of March 1988, one of them collapsed after the wind ripped out its polythene on the far side, see below for how that works.

How big?

I would buy the largest you can fit into your area, because the space is useful for storage and drying washing as well as for growing! One always finds more to plant in a tunnel. Hoops are 5 to 6 feet (1.5-1.8m) apart so length is multiples of that. I reckon that 20-30 feet is a good length for even ventilation, whereas tunnels of say 60 feet length can have pockets of ‘dead’ unventilated air in the middle.

My current tunnel is 42ft long, and works especially well for winter salads, without any supplementary heat.

Winter salads in no dig polytunnel in December
Winter salad plants 19th December 2019, before a pick for Christmas. They carry on producing new leaves until spring, from transplanting in October.

Orientation

  • North to south is ideal so that tall crops in summer cause equal amounts of shade to either side, also to reduce overheating in summer.
  • An east-west structure is face on to the midday sun and in a hot climate this is not ideal during summer. It also means some shading of crops in the north bed when summer crops grow tall in the middle.

However any orientation is possible and I have tried many, with success. Other important factors to consider are aligning a tunnel up-and-down any slope (beds across slope are harder to water and mulch), and having the doors at convenient points for access and watering

Ventilation

Plants like fresh air and its important they have enough, rather than striving for maximum heat. Air in a polytunnel circulates from one end to the other, and if possible I recommend leaving a gap between the top of doors and the frame above them, say 6in (15cm), so that a small amount of air can always flow through and increase carbon dioxide levels, without a draught at ground level. I find that winter salads stay healthy, without mildew problems, yet without any need to open and close doors for much of the winter. One job saved!

The option of side vents (instead of the polythene going to ground level) is in my opinion not necessary or suitable for vegetables in temperate climates such as here. Side vents reduce temperature in windy weather, while doors at both ends offer enough possibility to admit fresh air. Its cheaper and simpler to cover the hoops with polythene only, to ground level and below. Keep side vents for long tunnels only, above a length of 40-50 feet (13-16m).

Polythene attached at ground level, or buried?

I recommend burying the polythene all around in trenches of one spade’s depth, in order to have a polythene barrier in the ground. This protects against

  • pests entering, such as rabbits, slugs, cats and dogs
  • weeds creeping in, including couch grass, buttercup, bindweed
  • too much draught and cold air around plants’ leaves.
Filling a trench for new polythene at Homeacres, January 2013
Filling a trench for new polythene at Homeacres, January 2013

It is sometimes claimed to be easier and quicker to attach polythene at ground level to battens or rails. However this means you need to dig holes for the foundation tubes, rather than simply knocking them in. Also you may need some concrete in there for windy sites. All the fixings you need involve extra expense, and are only worthwhile if there is simply no room to dig a trench.

My First Tunnels polytunnel has base rails, professionally installed, and they are working well. I asked the fitters to leave a polythene skirt below the base rail (see photo), which we then dug into the soil.

Foundation tubes

When burying polythene in a trench, tubes simply need to be hammered into the ground about 12-18in (30-45cm), where their role is to give the structure some rigidity, that is all. When polythene is bured, the tubes are not anchoring the structure in place, but keeping it steady in wind.

In contrast to this, when polythene is attached to a rail and not buried, the foundation tubes have more importance as they are what holds the structure in the ground (rather than the buried polythene) and so you need more expensive tubes with metal brackets on their ends, and each one requires a dug hole, sometimes with concrete.

Crop support bars

Although an “extra” I would always buy these, so you have support for climbing plants from tomatoes and cucumbers to beans and melons. They span across from side to side at about or just over 6ft (2m) high, so you can walk underneath, yet also reach to tie strings or stakes.

How many years before re-cladding?

Polythene needs replacing every 5-8 years, depending how windy your site is and how tight you can stretch it. Polythene is easier to make tight when the cover is put on in warm sunshine, if possible. I have often done it in January and managed alright, but the skin is definitely slacker and more prone to damage than when clad in warm sunshine.

The First Tunnels fitters have achieved a tight finish on my 2019 tunnel, erected in May warmth. They reckon the polythene can last for 15 years! This tunnel is 12ft longer than my first one, same width, and has lovely straight sides.

New polytunnel First Tunnels
23rd May 2019 after two First Tunnels fitters had started at 11am the previous day, 18x42ft with lovely straight sides, and a polythene skirt from the base rails

What kind of polythene?

More types become available and choosing is then difficult. From tunnels I have seen with the more expensive thermic or anti-condensation polythene, I doubt that their extra cost is worthwhile. I recommend the standard, light-diffusing polythene which admits around 89% of daylight. Always use horticultural grade polythene, which has a uv stabiliser, without which it would be brittle and break within a year.

A friend recently noticed the great clarity of my standard, light diffusing polythene which is now 3 years old. I had recently washed it with a wet sheet and brush to remove lichen and moss.

Doors

You use these a lot so suffice to say, they are worth spending money on to have the ones you like. Home-made is certainly possible, note my tips on ventilation. Its the area where you can be most creative, especially if you enjoy carpentry. For door frames, 4×2 timbers are good.

Watering

I like hand watering, but it needs more time. I have two spray lines supplied by First Tunnels, and do not use them a lot because the distribution is uneven. There are several dry zones where we need to water by hand afterwards.

60 thoughts on “Polytunnels, advice on buying

  1. Hi Charles, you have truly been an inspiration for us to set up a fairly large veg garden and also a 14 by 35 feet polytunnel. And we’ve had lots of beautiful organic veg this year. As first time grower doing no-dig, the results had been phenomenal but I do need your help and advice on the maintaining the plants inside the polytunnel and on the polytunnel itself.
    1) We laid down quite a lot of cardboard to suppress the grass/weeds but didn’t realised, given the dry summer this year, that our polytunnel is actually built on a very wet and soggy area. With the advent of the rain in autumn, there’s quite a lot of cup fungus that have grown on the mushroom compost we have inside the polytunnel. How dangerous are they to the veg inside the polytunnel as I noticed brown spots on the cauliflowers and rust appearing on the leaves of the leeks? How can I prevent the growth of pig-ear/ brown cup fungus in the polytunnel?
    2) Why is there rust on the leeks as I watched your video on the garlic and garlic not affected by rust inside the polytunnel so I’m wondering what we have done to have caused the rust?
    3) We’ve got a current infestation of aphids (green ones/ winged ones and red/ brown ones) inside the polytunnel and we are losing the battle with just cleaning the leaves and spraying with a mixture of dish-washing liquid and garlic. They have spread to almost all the plants in the polytunnel including the bulb fennel plants and I thought they don’t like the smell of fennel. Can you kindly advise the quickest method on how to stop the infestation organically?
    4) Will the aphids overwinter in the soil and then come back again next growing season? (Note: the polytunnel is full of veg at the moment hoping to tide us through winter till the next growing season) How can we get rid of all the over-wintering aphids and larvae?
    5) Saw your video/ blog on cleaning the outside of the polytunnel (or is it in your book as I’ve a few of your books as well). What organic cleaning solution do you use for the outside of the polytunnel? Also how to and what solution would you advise to clean the inside of the polytunnel?
    Your advice will be very much appreciated.

    1. Nice to hear Jan, excellent for a first year.
      The boggy soil will improve in time thanks to soil life, but is a reason for plants struggling a little, and then aphids are attracted to them.
      1 That fungi sounds fine to me, it has decomposition work to do, just cut off the mushrooms when seen to clear space
      2 I have some rust on garlic, not a lot, should be ok and pull off the lower leaves to compost
      3 Best remedy is long term, add more compost to build fertility, soap etc is temporary only
      4 You can’t “be rid of them” but need stronger plants which don’t interest them
      5 Just water!

      1. Hi Charles, really appreciate your reply. Honestly, we wouldn’t have started our organic veg garden if we didn’t come across your information and books on no dig so thank you and Stephanie for setting us on this path. I think I’ve watched all your videos before embarking on this.
        To clarify with just a few more questions:
        1) Can the cup fungus be added to the compost?
        2) The plant leaves (eg. Cauliflower leaves with the aphids) should they be thrown away in the bin or can they be added to the compost? Will aphids / larvae survive composting?
        3) Are there plants that attract more aphids eg. tomatoes/ chilli plants? in which case I believe your book indicates companion planting such as basil/ marigolds? Will they help?
        4) I know your advice is to add organic compost plus homemade compost (not ready yet!) and mushroom compost and manure to add fertility. Will only mushroom compost be sufficient to add fertility or must it should be a combination for optimal soil fertility?
        5) We got a few tons of mushroom compost this year and added about 15cm to all the vegetable area. Do we need to top up for the next year’s growing season for added fertility or will it ok for one more year?

        1. Great thanks.
          All damaged leaves and plants can go on the compost heap.
          Yes dwarf French marigolds are great companions plus beautiful plants.
          Any compost brings fertility. You may not need to add any for another year, but 2-3cm will be nic food for soil organisms.

  2. Hi Charles! Great advice on starting out with a poly tunnel. Re the ventilation at the top of the doors. Do you mean leave a permanent gap? So not a gap that needs to be somehow covered during the depths of winter? Also, are you happy to recommend a poly tunnel company? I’ve just done a google search and First Tunnels looks good. But you may know of another.

    1. Hi Sally, and yes First Tunnels are excellent. The base rail is good so far here.
      And yes I have a permanent cut hole each end, all through winter

    1. These hold warmth but are expensive. Are perhaps difficult to clean after a few years, can last a long time before recovering is needed.
      Keder greenhouse for example, solid, storm proof, and expensive.
      Normal plastic tunnels serve well in most locations. I am happy with mine from First Tunnels.

  3. Hi, Charles,

    First things first – I just want to say thank you for all the incredibly useful information you make available both here and on YouTube. Inspired by you, my wife Carole and I are now moving our allotment over to no-dig.

    Our allotment is pretty small (30ft x 45ft) and 10 years after our association first secured the use of the land*, our Parish Council has finally agreed to allow plot-holders to have polytunnels, however, we are restricted to maximum dimensions of 2m x 4m or 3m x 3m – both substantially smaller than we’d like but beggars can’t be choosers.

    Clearly, the latter size gives us one extra square metre of space but I’m interested to know if you have any views on whether a rectangular footprint (albeit smaller) has advantages over a square footprint.

    I have a second more general question, too, if that’s OK. We accept we’ll never be able to grow enough fruit but do you think it’s possible or reasonable to expect for us, using no-dig methods, to become self-sufficient in veg on a plot of this size? The kids flew the nest some years ago, so it’s just Carole and me to feed. We intend removing the boards from most of the raised beds and believe this should help bring more of our plot into production as paths will become narrower and, in some cases, no longer needed.

    Apologies for monopolising your time!

    Many thanks,

    Best regards,

    Ozzy

    *Can’t tell you how much I wish I’d discovered no-dig ten years ago – the money and time I would have saved, not having to build and then replace raised beds!

    1. Thanks Ozzy and I would go for 3×3, the extra metre!
      You should be able to grow almost all your veg. Avoid low yielders like Brussels sprouts and asparagus.
      Do lots of inter- and succession planting. A good project.

      1. Thanks, Charles – will be guided by you!

        Interesting comments about the asparagus – we already have some that were a gift but they haven’t done well and I was planning to move them but will have to rethink – and the Brussels sprouts (one of my favourites but you can’t have everything!). I take it we’d be OK with other brassicas?

        Thanks again,

        Best regards,

        Ozzy

  4. Just a quick question I am about to get a Polytunnel for flowers mainly should I place it sideways to sun or ends to sun. Thanks

  5. What do you do to stop it getting too hot in summer? Our greenhouse reaches 30+degrees for long periods of the day. Were in south Cotswolds.
    Thanks

  6. I am admired with your article on tips to buy a polytunnel as myself also got into problem several time while choosing the best polytunnels. I really appreciate your hard work writing these actionable tips to read before buying a polytunnel.

  7. Do you have any experience of these carbon fibre polytunnels? I’m looking at those As a permanent fixture, but obviously I’ll anchor it well… just can’t seem to find much out about them so just presume they’ll have the same benefits as a polycarbonate greenhouse as opposed to glass…..

    1. I am not sure Nicola, know they are expensive and you could buy twice the size polytunnel with ordinary plastic, that would be my option.

  8. Hello Charles,
    We stay in the HIghlands , a very windy area!
    We are looking into getting a polytunnel measuring 6ft wide by 18 ft , we can go up to 20ft , this will hopefully be placed North to South and alongside the croft wall, with a banking of small trees the other side so fairly protected from snow and wind. A lot of firms have mentioned base plates, the area we are planning on putting it is on grass, can we do without base plates what is needed to make it sturdy. Also are two doors needed can one door be sufficiant. Thank you.

    1. 6ft wide is tiny! and yes two doors needed. unless you cut a small vent hole one end, ask the suppliers, probably needs two doors.
      Needs a hole dug for the plates, no way around that. Grass regrows fast!

  9. Charles ,

    I am erecting a 16x27ft polytunnel soon – I am keen on applying your no dig technique(which I find extraordinary may I add), though do you recommend this with raised beds or just apply a few inches of compost on layers of cardboard and start planting ?! Thanks and keep up the excellent videos on YouTube

    1. I would not lose precious polytunnel space to wooden sides, just no need.
      Cardboard is only if you have thick weeds to deprive of light.
      You will grow a lot of food.

  10. Thank you very much Charles will do. Have you seen this work out well? Or do you think I should take the concrete out? Best Jonathan

    1. If I had time, I would always take the concrete out.
      I have seen successful beds on paving slabs, with gaps allowing water to pass though.

  11. I would like to have a 10′ x 20′ polytunnel for growing vegetables( not root apart from beetroot) salads and squashes but the best place to locate it is on concrete( an old silage pit ) This means raised beds inside – is 12″ soil enough? and how do I manage drainage issues? A layer of gravel at the bottom? Or should I either break up the concrete – or find another site? Many thanks

    1. Hi Jonathan, yes this is possible, if you can anchor the tunnel to the ground!
      Definitely break the concrete to allow water to pass downwards. Cracks in the concrete should be enough, check first to see how deep it is and whether you can break it!

  12. I have recently bought a house near Sheffield with an acre and a half of land which was used by the previous owner for horticulture. My plan is to have a no-dig vegetable garden of half an acre, growing “in season” produce for a local restaurant. There are two old 10m x 30m polytunnels on site which appear to be too big for my needs. Approximately, what size of polytunnel will I need to supply the vegetable garden with sufficient seedlings to allow as many crops as possible per year? The main crops will be staked beens, leeks, onions, broccoli, garlic, lettuce, cabbage, aubergine, courgettes, beetroot, spinach, cavolo nero, and peas.

    1. Yes Paul those are big tunnels.. for propagation, you need say 10 square metres/110 sq. ft.
      But aubergines need polytunnel conditions to grow, and the tunnels will be useful for winter vegetables especially eg kale and lettuce.
      Hope you can open soon 🙂

  13. Was wondering if you’ve come across the Keder Greenhouse and what you’re thoughts were on this type? They use a unique Kederbahn bubble plastic and rail system which seems quite good. Apparently they are more cost effective than a traditional glasshouse, and also stronger and more durable than polytunnels.

    Thanks!

    1. “Cost effective” hmm, they are expensive Simon!!
      May be worth it for cold and windy areas, otherwise a strong-hoop polytunnel is most cost efficient, easily

  14. What about soil never getting washed by rain under polytunnels? Can this be an issue in the long run? Such as salt accumulation..is that a thing? Thanks for another helpful article

      1. Hi Charles, when you say ends do you mean where the doors are?
        Many others on the net are saying not to do this, can you tell me why you recommend this from your experience, if I understand you correctly

  15. Hi Charles, this is such a helpful article, thank you so much. You say orientation North to South. Would you think a slight north facing slope would impact heavily? Alternative is to go across the slope east to west. With a south-west prevailing wind, how would this affect orientation? Also do you know about need for planning permission for polytunnels? What is the max size before needing planning? Many thanks, Olivia

  16. Hello Charles, I live on high ground 8 miles from the sea and I have 3 20×10 polytunnels but have not seen put them up here because one flew away at a more protected site. I might get a profession polytunnel company to put up a new one. What is your advice please. Also in answer to your previous correspondent, i had a small polytunnel and it was marvellous, you can grow a lot of especially if the beds are reasonably deep.

    1. Nice to hear Mel and on your windy site, it’s probably worth paying professionals to erect the tunnels.
      First Tunnels did a fantastic job on mine, apart from a small mistake on the irrigation, but that’s a detail 🙂

  17. My allotment field only allows tunnels up to a max of 3.5 by 2.5 meters, do you think that this size is worth having. Took on a second allotment recently and used no dig with cardboard and leaf mold and now have a weed free set of beds although we had teething problems as the local foxes and cats kept digging it up and letting the weeds through.

  18. What would we do without Charles
    I am completely addicted after meeting a colleague who told me about him and no dig while on a course in Coventry University in Social and Therapeutic Horticulture
    He has changed my life for the better ….
    It really works better than all the other methods I m sure after trying things myself as he recommends…
    Proof is in the pudding
    Joyce Fitzpatrick
    Ireland

    1. Hello Joyce, and thanks so much for writing, and I am happy to help.
      I’m pretty sure that your contact was Lara, who also is special, and that course sounds so worthwhile.

  19. I’ve never done polytunnel gardening. I live in South Carolina, USA on the coast. What would you suggest? What brand? Thankyou

    1. Hi Barbara, afraid I do not know the USA brands but you call them hoop houses. Look for one with sturdy metal hoops say 2in diameter in case of high wind, I suggest 14ft minimum width and any length, make sure you have water available.

  20. Thank you so much for this wonderful article!

    I am a beginner gardener and my allotment is not close to the house. Should I buy a tunnel or a small greenhouse (my garden as well as all the alotments around me have a rat problem that becomes more difficult in the winter and rat poison or traps are not 100% efficient)? The greenhouse would have glass walls, aluminum supports and a brick and concrete foundation on top of which we would put soil and compost in oder to keep rats out.

    Sincerely,
    Alexandra

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