How to build a £30 DIY greenhouse

Simon Mitchell
Friday, 20th April 2012

Greenhouses are essential for exotic crops and four-season growing. But there's no denying they are probably the most expensive thing you will ever buy for your garden. How about if you could make your own, and for just £30? Interested? Read on...

Ever since I learned about Buckminster Fuller at art college, I have wanted to experiment with making human-scale geodesics. So, as part of a new project – a book on DIY greenhouses on a budget, I constructed a surprisingly large greenhouse using wild hazel wood and a purchase of £30 worth of polytunnel sheet (which is about $50 for my USA readers at time of writing). This article outlines the procedure for building the structure – without too much detail of course – because I want you to buy the book when I have finished it!

The first type I wanted to build and the most basic shape was an icosahedron, a 20 faced sphere recognised even by the Ancient Greeks – it is one of the Platonic Solids (Tetrahedron, Cube, Octahedron, Dodecahedron, Icosahedron).

An icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is a form found in nature, for example some viruses have icosahedral shells.

Every day my springer spaniel, Freya, needs a walk, so when we went I out I would find and cut myself the longest length hazel rods of a useable diameter I could find (in addition to providing numerous sticks for the dog).

Over the course of a couple of months of winter I built my collection of straight sticks up to the 30 I needed. I trimmed them down to an optimal length of 196cm and laid them out ready to construct the shape.

The size of your dome is going to vary a bit depending on how you connect the struts to each other. There are several tried and tested methods for this. In an icosahedron each vertex (the singular of vertices) joins five struts – a very complicated joint for joining wood to wood. So for this basic dome construction I used a very simple method of drilling holes and connecting the struts with wire and rope. In order to stop the ends of my hazel from splitting, I lined each hole with a bit of used copper pipe.

I moved the top to the centre of the cylinder and set it up in a tipi shape. I untied each top vertex, re-threading the rope in some instances to allow for 'settling' of the wild wood, then attached the top struts. I supported the roof with a large stick for the last two struts. Six more reef knots and the basic structure was complete. I included a central pole to add stability to the structure, slightly lifting the roof to tighten the dome up. I took another photo of my 'greenhouse' and published it on Facebook where friends and family could take the mickey out of me for building a greenhouse with no glass!

The covering for this dome arrived the next day. I had ordered three 7.3 x 1m Sunmaster Tunnel Covers, but it arrived all as one big sheet. I cut oversize equilateral triangle sections and nailed them with small, flat-head, roofing nails onto the framework, folding over the sheeting to produce a stronger edge. This is where the fresh-cut timber came into its own – as it was still sappy it took quite a lot of pounding without splitting at all. Three (oversize) equilateral triangles fitted the width of sheet and allowed for anomalies created by the wild wood and the foldover onto the struts. I later tidied-up these edges with a staple gun.

This dome is now full of seedlings as I write. I suspect I may have to tie it down when it gets very windy but that should be easy enough. It is not quite as warm as a glasshouse but certainly performs well in passive warmth capture as all the seedlings are sprouting.

My next project is to build one of these with every large triangle subdivided by three (e.g. nine trianges in each) – a 'three-frequency, five eighths, alternate icosahedron' – which is more of a dome shape.

This article is first appeared on Simon's website, www.simonmitchell.co.uk, and is reprinted with Simon's kind permission. To find out more about Simon's book, visit www.makeagreenhouse.co.uk 

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