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The polytunnel sporadic blog

Posted: May 20th, 2017 | Author: | Filed under: Uncategorized | 1 Comment »

Around a year ago, we built a 110 square meter polytunnel, mostly from recycled materials. Total cost was around £300, which covered the plastic and some nuts and bolts. The wood for the 4 raised beds came mostly from the fire pile of a local sawmill (so we ended up with some beautiful pieces of oak to make the beds with), and we used a modified version of the Hügelkultur idea, which is to say that the bottom half of the approx. half meter deep beds are filled with big chunks of wood. This wood gradually breaks down over time, releasing fertility and heat to the soil above, but in the first couple of years, it robs nitrogen from the soil as the decomposition process begins. The modification to this process that we made was to add wood chip to the big pieces of wood, with the theory being that this would help initiate decomposition faster (given that smaller items rot faster). To alleviate the loss of nitrogen from the soil (as we had no good soil to begin with), we added a layer of biochar, because it’s a rich source of nitrogen. Atop that is around 30cm of any old soil we could find, typically quite heavy clay soil. The exception to that was the 4th bed, which had no soil at all, just rotted woodchip on top. That’s led to a, uh, healthy population of woodlice (I suspect there’s tens of thousands of crustaceans in that bed), but no apparent difference in the fertility of the soil. We used a lot of nettle tea (a rich source of nitrogen) on all the beds last year, so despite the poor quality soil that we started with (or even complete lack of soil, on that 4th bed), we had immediately healthy, fertile soil, with abundant growth.

That’s a potted history of our polytunnel; it took around 3 months to build, and it’s now in its second spring. We’ve got lots of greens growing, from spinach to mizuna to rocket to plain old lettuces, plenty of beans and peas, tomatoes, squash and a half dozen bathtubs full of carrots, coriander, beetroot and basil. We tried a few of the edible weeds last year, but this year the only thing that we’ve let grow (because other plants such as chickweed didn’t provide much yield) is wood sorrel, because it’s delicious! It’s got a lemony, rockety sorta flavour, and is such an unassuming little plant, I’ve let it spread where-ever it’s established itself. Which has had the fun consequence of allowing us to watch wood sorrel flower and go to seed, as we discovered that it doesn’t rely on insects or even the wind to spread its seeds; the seeds explode outwards from the seed pods as they dry out and become brittle, at which point a gentle brush sends seeds flying everywhere. We spotted them getting up to 30cm away, not bad for a tiny 1mm seed! You can just about spot them flying around in this video:

Amazing exploding wood sorrel seeds! We bagged a few seeds and I’ll help that little patch of sorrel along, as it’s in the shadiest corner of the polytunnel, suitable for a woodland plant.

Next post will be a quick tour of the polytunnel, suitable maybe for its first birthday! I’ll try to get a few photos together from the building process too, as it’s fun to see that previously unused space turn into the lush, green haven that it is now.


One Comment on “The polytunnel sporadic blog”

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