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The first year in a polytunnel: planning, beds and seeds

If you’re thinking of putting in a polytunnel here are some tips on how to plan everything – including filling it with your first plants. Don’t just jump in! There are some important decisions to be made that could affect the environment inside for some time to come.

The chances are, given that everything usually takes longer than we expect, if you planned on putting up a new polytunnel in time for the growing season you probably ended up being slightly late. Putting up a new polytunnel is a lot of work and if you’ve never done it before it’s hard to estimate accurately. The cover, for example, should NOT be put up on a windy day – unless you like flying huge kites…

Once it’s up, you have a new and quite wonderful gardening space that can give you years of extended growing seasons and delicious crops. But first, you have to create the beds.

Preparing these takes yet more time as well as a great deal of effort. And, unless you’re in the happy position of delegating this to someone else, it will have fallen on your shoulders. So the big question really is, do you prepare the beds before or after putting up the tunnel?

Planning your polytunnel

Whether you actually construct them or not, at least plan the beds first. Don’t leave this extremely important step until the tunnel is actually up! But, it may not be practical to actually finish creating the beds before the tunnel goes over them. Raised beds, especially, might be a serious obstacle when putting up the tunnel – and you really don’t want to trip over them when you’re carrying a heavy hoop section. For instance, if a raised bed occupies the central space, remember that in order to fasten the ridge to the hoops you’ll need to be standing on a stepladder – and it’s not easy to position this on top of a raised bed!

raised bed, image

While it would be great to have a bed such as this in place before the tunnel goes up, you need to stand on a stepladder to fix the ridgepole to the hoops…tricky!

However, if you think you can deal with this, then definitely put the beds in first. Otherwise, at least remove all the turf (unless it’s been very wet and the result will be a quagmire) as by doing so you’ll also remove many of the pests that will otherwise be left inside. You can also clear weeds and undergrowth away from the tunnel wall area, difficult (and risky!) to do once the cover is in place.

Compost and manure

Digging compost / manure / soil amendments into the beds is, obviously enough, a great idea – and it’s much easier to do when the whole area isn’t enclosed by the cover: wheelbarrow access isn’t restricted, and you don’t have to worry about getting too close to the walls while wielding a spade or fork.

Polytunnel space is far too valuable to waste and should be used efficiently. No matter how big the tunnel, next season (or next week!) you’ll wish it was bigger still. However, don’t make the mistake of thinking that a space 25cms wide alongside the tunnel wall will be enough to allow you access to that side of the beds, because it won’t. The tunnel wall will typically begin to curve inwards roughly a meter off the ground, and a good rule of thumb for every path in the tunnel is that you should be able to walk along it pushing a loaded wheelbarrow without having to bend double in the process.

Many people prefer to grow in raised beds, and these are an excellent tunnel option: they’re not compacted through the use of adjacent paths and, being higher, they’re more accessible. Just don’t make the mistake of using the tunnel cover as one of the ‘retaining’ walls of a raised bed, because while strong it’s not made for that kind of stress.

Time your seedlings

Ideally, seedlings should have been started elsewhere (on a well-lit windowsill and / or in a cold frame) roughly a month before you expect the tunnel to be ready. If you timed this right, you’ll have lots of plants ready to go into the waiting beds. If not, all your work just sits there while you wait for the seedlings to grow – what a waste!

seedlings, image

White plastic plant labels can be cleaned and used again and again.

White plastic labels, written on and stuck into the pot, are commonly used to identify seedlings. These can be used over and over again, but each time you have to remove the writing from the previous planting. Fortunately, this is easy: rub with a bit of wet earth between your finger and thumb, and the writing will vanish – so long as you used a soft pencil in the first place! Give them a wipe to remove the mud, let them dry and they’re good as new.

Sowing seeds usually takes far less time than everything else, as everything is on such a small scale. Once plants are established, weeding, pruning, clearing excess growth, setting up watering systems and tying up etc take far more time.

Don’t forget to allow some space for staging, or you won’t have anywhere to fill pots, sow seeds, mix soil media, store tools and nurture seedlings. Staging is an essential part of a polytunnel, and there are some great kits available – or, you can make your own.

staging, image

Staging can be made from scraps, or purchased as a kit.

If there’s enough room, a comfy folding chair isn’t a bad idea either, so you have somewhere to sit after a hard day’s work or a cosy spot in which to ride out sudden downpour. Believe me, you’ll really appreciate your polytunnel when it’s bucketing down outside!

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13 Responses to “The first year in a polytunnel: planning, beds and seeds”

  1. Clare Smith says:

    I have spent months clearing the site for a polytunnel in my garden,so I can fit in one that’s as big as possible in the space I have while allowing for 2′ all around for access.It’s now end of September so time to start looking around for a secondhand one or may make one if I can get someone to help me!Your book has been a great help!

  2. Mark Gatter says:

    I’ve put up a polytunnel with NO space between it and the adjacent hedge, and it’s a bit of a nightmare as I have to keep an eye on brambles, hawthorn etc and trim regularly. And I always get both scratched and stung in the attempt!

  3. Ray Gascoyne says:

    I am planning to build a DIY polytunnel this winter and hopefully have it ready for the cover on some calm sunny day mid spring. I’m aiming to make it 20’x12′. I have an old Scaffolding Tower consisting of 9 H-bars and 5×21′ lengths of yellow 50mm plastic gas piping. Just need the timber then I’m ready to go. Unfortunately I have a more urgent task to perform first. I must replace one side of my timber greenhouse which is rotting at the bottom. Not to worry, winters are long and I’m retired (73) so I should achieve my aims.
    Anytime I can’t get to my allotment through bad weather I spend reading your book (GROWING FOOD IN YOUR POLYTUNNEL) or sourcing the internet for polytunnel information.

  4. Andy McKee says:

    Good luck Ray – send us a photo of your DIY tunnel when the cover goes on!

  5. helen says:

    Have just erected my first polytunnel, started planting my seeds and am so excited. My early potatoes are chited out and nearly ready yo plant so cant wait.

  6. Stephanie says:

    I have just finished putting up my first polytunnel (after many years of yearning!) and am already wishing I had gone for a bigger one – mine is 10′ x 20′. As I live in South West France, I am expecting to use it mostly to start things early and to be able to have fresh veg throughout the winter. I doubt it will beused during the summer as it gets so hot here. I have been surprised today, which has been a mixture of sunshine and downpours, to see the temerature inside fluctuate between 20 and 12 degrees in a matter of moments, with both doors shut. Also the temperature at around 7pm was about 2 degrees colder inside than outside! Any advice or comments on anything I have mentioned would be very welcome. Also just wanted to say how much i enjoyed reading your first polytunnel book. So helpful, straightforward and un-intimidating. Looking forward to starting to read the other one.

    • Andy McKee says:

      Hi Stephanie – The more stable you can keep your tunnel temps, the better. With a small tunnel like yours there’s less ‘thermal mass’ to keep temperatures stable, but even so it shouldn’t hammer up and down like that. Take a look at how much air is getting in around the doors – but mainly, put your thermometer somewhere the sun isn’t shining directly on it.

      My guess for it being cooler inside than out in the evening is that some warmer weather arrived. Naturally the tunnel would take a while to warm up to match it.

      If this is a regular occurrence then you have some kind of microclimate effect in play from a nearby road or geological feature, so you might need to delay your shutting up time to take advantage of the heat during winter.

  7. Sian Hughes says:

    I am a support worker in a house for adults with Autism and additional learning difficulties and we have just purchased a 4mx2m PT with the intention of giving our service users an all year round activity. I read what you say about preparing the ground prior to installing the PT and have taken that on board my worry is that we won’t have a great deal of space for growing once we allow for access. Have you any design ideas for plotting the growing space we could use and any other handy tips would be very much appreciated.
    Kind regards

    • Andy McKee says:

      4m x 2m doesn’t leave a lot of space for access adjustments, but this document might interest you. Other than that, keep the layout as simple as possible (minimum paths) and use suspended shelves to provide additional space for containers.

  8. Simon Deak says:

    Hi Andy
    My question is what do you do about soil managment in a polytunnel as the years go by?

    • Andy McKee says:

      That rather depends on your soil type and how you grow, but if you add organic matter once or twice a year and supplement the soil to offset what you grow it isn’t usually a problem. We’ve got a whole chapter dedicated to this in How to Grow Food in Your Polytunnel.

  9. Roofgardener says:

    Nice article Andy.

    I bought my first PT about a year ago, for an asphalt Roof Garden. It’s only 3m x 2m, but it has revolutionised my “Gardening”.

    It’s big enough for a Comfy Chair, and I’ve chased electricity out to it, so it has a fan heater, electric lighting, a radio, soil warmers, and a rather optimistic LED “Grow Light”.

    Being on asphalt, pooled water in the Roofgarden would leak under the edges and somewhat flood the floor, but I put down some plastic mesh matting, and now I can walk around in my Comfy Slippers without getting we feet.

    Condensation is a major problem in Winter, but I have plans for that. It also blew away once… but I’ve since weighed it down.

    It only cost about £70 (including postage), and has revolutionised Roofgardening Life. Finally, a comfortable, roomy area for me to pot and plant in. It really encourages me to spend time after work each night, something that I never did in Winter before.

    Warm regards,

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