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6: A new polytunnel – the beds

Inside the polytunnel, the width and position of the beds and paths inside it is the most important piece of planning you will do. While it’s tempting to make the paths narrow, resist the urge – you’ll be spending a lot of time in the tunnel, so don’t leave yourself short of work space.


Even if you’re trying to maximise your veg-growing space (and who isn’t), don’t forget to allow plenty of room when you’re planning paths. To allow you to get through with a loaded wheelbarrow as well as room for kneeling down, paths should usually be between 50 – 75cms wide. It’s helpful if they have a clearly defined edge so that you know where the path stops and the bed begins. The boards at the sides of raised beds do this for you, but for soil-level beds a row of bricks or narrow planks will do the job.

digging pic, image

Cut out a slab of earth, and turn it upside-down

Stepping off the path onto the beds is a bad idea, because it compacts the soil. If your path layout leaves you with awkward spots to reach (and sometimes this is unavoidable), keep a short plank to hand and lay it on the soil to use as a stepping stone when you need one. This is an old gardeners’ trick to spread your weight out, and causes far less compaction than your foot alone.

Digging the beds

Once the plan is ready, it’s time to start digging. If the ground being turned into beds has not been cultivated before, it will be rough grass and weeds. The easiest way to deal with it is simply to cut it into chunks with a spade and turn them upside-down. Over time the inverted turf rots down into compost, and this is adequate for most types of fruit and vegetables. Double-digging is exactly the same, except you put the turf to one side while you remove the soil to a further spade’s depth, so that the grass goes right at the bottom.

Whichever method you use, digging will clearly define the bed area. Once that’s done, it’s time to lay weed-proof path membrane. This can be tucked down into the edge of the beds as shown.

membrane pic, image

Tuck the edge of the membrane down into the bed


Raised beds

If you’re creating raised beds you’ll need boards for the sides, and stakes to hold them in place. Visit your local building supply merchant and check for a skip of unwanted off-cuts of wood. If you’re lucky you’ll find some lengths of 25 x 50mm timber – but make sure they’re untreated. If you can’t find any in a skip, they’re usually cheap enough to buy. Cut them into at least 50cm lengths (assume roughly 25cms below the ground at least that much above it) and trim one end to a point. When hammered firmly into the ground, these will hold the sides securely.

Scaffolding planks

These make ideal sides for raised beds. Call your local scaffolding company and ask if they have any damaged planks for sale. They’re not allowed to use these on-site, and usually have a few available. Tell them what they’re for, and they’ll probably know exactly what sort of thing you want. Gardeners have probably been calling them for years.

siding pic, image

Sharpened 20 x 50mm stakes will hold the siding firmly in place

Remove the protective brackets from the ends of the scaffolding planks, cut them to size, and lay them flat alongside their final position. Scaffolding planks are hefty pieces of wood, and if you’re cutting them by hand you won’t need to go to the gym for a day or two. A chainsaw is much faster and easier (after all, the digging was strenuous enough, wasn’t it?), but don’t use one unless you know how to handle it. Always wear ear protectors, goggles and gloves, and don’t be tempted to use a chainsaw inside the tunnel – not only could flying chips damage the cover, but the noise is unbearable.

Planting up

Whether or not you decided on raised beds, spreading plants such as squash will flop all over the paths unless you plant them far enough away from the edges. Being somewhat brittle it’s difficult to point them where you want them to go. Other plants may surprise you: bush beans, for example, might stay fairly small in an outside bed…but in a polytunnel the climate will be so much more to their liking that they may grow better and faster – so be prepared for plants to be considerably bigger than you’re used to.

finished bed, image

Stand back and admire the result...and then get planting!

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13 Responses to “6: A new polytunnel – the beds”

  1. lynne says:

    at the moment I have a cultivated site, so opefullt not loads of digging, shall I raise the beds? Is this better? and what about keeping the weeds down?

    • Andy McKee says:

      If the site is already cultivated there’s no real advantage in raising the beds, and it does make some work because of the edge maintenance. Deal with weeds the same way you would outside, so I would be tempted to membrane the paths and cover them with gravel or chunky bark.

  2. Claire Kelly says:

    I am just about to put up my first polytunnel tomorrow – 18′ by 36′. I have been growing my own for a while now and am so excited at the chance to extend my growing season. I have been devouring your books for the last year to “learn” what i need to get me started.

    Many thanks

    • Andy McKee says:

      Good luck! Don’t be fooled by the rain – you’ll need to start watering from day 1. Start thinking about what you want to be eating in 6 months, and get planting!

    • Helcatt says:

      Any good book recommendations? I’m hoping to get a PT next year and keen to do some research!

      • Mark Gatter says:

        Be still my beating heart – yes, I think we can suggest a couple…if you haven’t yet bought a polytunnel, have a look at ‘The Polytunnel Handbook’ by Yrs Trly and Mr McKee. It’s intended for people wanting to take the plunge but with a few unanswered questions. And, of course, if you have other questions after, please get in touch. Then of course there’s book no. 2 which covers how to actually grow stuff – all year round. Both are available on the home page of this site. Let us know how you get on. It’s definitely a good idea to wait until the spring before putting up your PT. There are only a few crops you could plant for winter at this time of year, and even if you put it up now it would still take a while to get everything ready. Much better to wait until spring so it doesn’t just sit there getting battered by winter – and you have all that time to prep the area instead.

  3. Neil says:

    Our new 14×40 polytunnel goes up next week, six months after we bought both your books. We’re going to do raised beds, but I have one question: would beds filled 100% with compost be too rich, or should the compost be cut with clay soil, which is the predominant soil around here (Aberdeenshire)? If so, in what proportion.
    I ask because there’s a company near us which is manufacturing industrial quantities of compost from a modern factory, using hundreds of tonnes of horticultural cuttings and prunings, council-parks’ waste, and similar vegetable matter from all over the county. It’s selling the stuff by the lorryload and very cheaply. I hear great things about it from farmers who have bought it as soil improver, but I just wondered if 100% compost is too much.

    • Andy McKee says:

      That depends on the quality of what they’re producing, but typical ‘green waste’ composts aren’t terribly satisfactory. They’re too coarse for seedlings, although you can get around that by top dressing and using modules. They’re also usually still composting when you receive them, and will slump considerably especially during the first year.

      Make sure that you get a look at a good sample before you buy, and decide then; I’d go for no less than 25% soil, keep a close eye on the nutrient balance of the resulting mix, and overfill the beds to compensate for the slump.

  4. Mark says:

    Why does the raised bed wood need to be untreated?

    • Andy McKee says:

      Because wood treatments will leach into the surrounding soil to some extent. Some products are known to be hazardous and they should be clearly marked, but if you’re buying treated wood you may not know what has been used. If in doubt, avoid!

      I should mention that it’s not just human health that concerns me here but the microbes in the soil. Tanalith ‘E’, a common biocide used in pressure-treated timber, is water soluble and can affect soil micro-organisms for several years as the product leaches out of the wood. So if you do choose treated timber, line the wood with polythene.

  5. Christine says:

    A short ‘thank you’ for the articles on your website. I bought an inexpensive 12’x20′ ‘garden’ Polytunnnel with a heavier than average frame (which should mean I can replace the cover when it inevitably roots) and it went up on Good Friday this year. I’ve already had the odd mishap, like not realising the effects of a sunny morning after a frost and losing tomatoes and Basil, so I’ll be adding your book to my birthday list this year

  6. Christine says:

    A short ‘thank you’ for the articles on your website. I bought an inexpensive 12’x20′ ‘garden’ Polytunnnel with a heavier than average frame (which should mean I can replace the cover when it inevitably rots) and it went up on Good Friday this year. I’ve already had the odd mishap, like not realising the effects of a sunny morning after a frost and losing tomatoes and Basil, so I’ll be adding your book to my birthday list this year

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