Pop-up Polytunnel

by Penny Armstrong -

Over the last few years we’ve become what could be loosely called experts in the ‘pop-up’ salmon pipe & plastic polytunnel. Bare ground to planted up in ten days. Fair enough, we do have help; our own excellent team of local volunteers, our WWOOFers and, on more than one occasion, the Moving On team. It’s all in the planning and preparation. There’s a knack to getting the pipes up and the skin on. A few hours of labour digging the trenches and making the doors. The real marvel though, is the preparation of the beds inside the tunnel.

Neither the ground nor the climate in Shetland is perfect for growing the more unusual vegetables we’ve become accustomed to buying from the supermarket. Our soil is very acidic and is either shallow and stoney or deep and wet. Clay, sand, peat or rocks and of course, the wind; constant, unpredictable and often destructive. So we use the tunnels to create better conditions for these types of plants, but what do you do about the soil? We’ve chosen to put our tunnels in the most sheltered area on the croft and this land is some of the shallowest and stoniest we have. We don’t want to use the big flat area, it might be deep and less stoney but it’s too useful for growing the crops that don’t need shelter and the tunnels would be far more exposed at the height of the winter gales. So for us, the answer is to build up the soil and fertility inside the tunnels as we go. We have 5 tunnels altogether and we have built up the soil in all except one. It started out as an experiment three years ago, after a mad middle of the night idea.

I was panicking about the lack of soil depth for the deep rooted sweetcorn, due to be planted out within the week into a new tunnel that was still just grass inside. In May and June we are always frantically clearing the weeds which have grown on the beds of our large flat growing area outside, ready for sowing and planting. We usually pile them up and allow them to compost if they have not flowered or produced seed. That year we decided to kill two birds with one stone and lay down the weeds in the polytunnel to form the basis of the beds. Next came a thick layer of seaweed and then another layer of rotted manure. A final layer of loam (well-rotted turf from the original clearing of the outside beds and rooting up by pigs) was added making beds 15cm deep. To top it off and prevent any of the weeds making it to the surface, we put a top covering of paper mulch (flour bags from the local bakery) held in place with sand, into which we cut slits to plant through.

It worked a treat. The courgettes, pumpkins, marrows sweetcorn and cucumbers, all of which relish a rich fertile growing medium and don’t withhold fruit if conditions are nitrogen heavy, produced very well. At the end of that season we understood just how much effective feeding influences production. Each courgette plant gave 20+ fruits and carried on producing well into October.

At the beginning of the following season the layers in the polytunnel bed had rotted and mixed into good textured soil, still fertile but not excessively so. In its second year we used it successfully for tomatoes, aubergines, peppers and chillies. Each year the fertility declines a little as each type plant takes what it needs; year three is for Florence fennel and finally in year four the French beans. We now incorporate this heavy layering of nutrient rich organic matter into our polytunnel rotation. The tunnel hosting the Cucurbits (marrow, courgette, pumpkin etc.) gets the application of seaweed and manure and each time we do this the soil builds into a deeper more productive medium for the plants.

Since then we have used the method for creating beds in two more tunnels tweaking the process as we learn. With the latest tunnel we put the paper layer directly over the weeds followed by seaweed, manure then loam; soaking each layer well as we went. We can then plant directly into soil; the paper rots away more quickly and we’re not tripping over it all the time.

Our latest tunnel was constructed at the end of June last year and we didn’t get round to sorting out the beds until it was needed for planting this spring. Not quite so ‘pop-up’ this time. It had been used for the storage of lime, bags of ess (ash) and Alan’s drum kit and was pretty weedy and full of bugs before we started. We let half a dozen hens scratch for bugs for two or three days before we started making the beds in earnest, then we got on with wheelbarrowing and spreading. The process was hard work but quick. Thanks to our WWOOFers and their persistence, polytunnel number 5 is up and running

From storage area to sweetcorn heaven in 10 easy steps….

Posted in: Growing Food, People