Build your own polytunnel or greenhouse



There are hundreds of different garden greenhouses and poly-tunnels on the market and whichever one you choose it will never be big enough, so make sure you build or buy the biggest one that you can afford, in the space available from the start.

Video- Mr TK builds a polytunnel  watch it on You Tube.

 I built my own based on a larger version that I used to grow in when I worked in Portugal.  It is roughly 5m x 5m.  2.3m high in the middle, and 1.7m high on the sides. These dimensions were slightly governed by the wood that I could purchase from a large DIY store. The wood that the roof sits on were poles purchased cut in half, so there are no sharp edges. I secured the roof support poles to the center uprights with noggins, so there again would be a smooth run over the ridge for the plastic. For the sides you can use 50 x 50cm treated wooden lengths.


 The reason I chose to build my own was that it is far stronger than most poly-tunnels and to have one the same size would have cost nearly double. Mine cost me approximately £500 in total.


Fit the strongest plastic you can find to cover a poly-tunnel. Mine has lasted 10 years.

The other reason to have a wooden greenhouse, is that it is far easier to run wires down it for crop supports.  The special plastic I used should last three to five years minimum and is available on line, mine has lasted over 10 years. Just make sure you order enough to cover the whole structure side to side in one length. The ends you can fill in after.

As you can see the structure is fairly strong. I added so extra support trusses inside, to the roofing struts. I will have to change the plastic in a few years, so there should be no problem getting on the roof to do this.


 It has now been up for 10 years, and we have had a bad winter with three lots of heavy snow, and very strong winds, so I feel it is a pretty strong structure. On reflection I would have added roof ventilation, which I still can do with a couple of windows on hinges. Side ventilation is OK, but for the best results if you have hot spring and summers then roof ventilation is the best option. I do leave both doors open once the season warms up, but I put netting across so as not to get any wind damage.



·        Remember, the bigger the better in the long term.

·        Find a sheltered spot that gets plenty of light but away from heavy winds.

·        Decide if you want a glasshouse which will be easier to heat and hold heat. Or a poly-tunnel which will be far cheaper and probably give you a bigger growing area.

·        If building your own poly-tunnel invest in heavy duty polythene coverings with UV protection. First Tunnels in the UK offer UV stabilised film is 200 microns (800 Gauge) and is supplied with a seven year guarantee.

·        Think about ventilation, most glasshouse will have this built in. Off the shelf poly-tunnels, might have some side ventilation. Building your own you can add roof ventilation.

·        If you are going to grow in large pots or troughs, then you can site your greenhouse anywhere, even on concrete or gravel.

·        Have a good water source close by, even gutters on the structure to collect rainwater. Tomatoes are very thirsty plants. 

     Pros and Cons Greenhouse 

  •      Greenhouses are more visually appealing constructions
  •      Site preparation requires a lot of effort. The base must be firm and flat.
  •      Greenhouses will be more expensive, but will last a lot longer and not have to re-covered and   withstand bad weather more. 
  •      Greenhouse will have less humidity that a poly-tunnel, so there is less chance of diseases spreading. They also hold more heat, so cheap to heat and overwinter plants and can resisit a light frost. Greenhouses offer maximum heat retention and better light transmission.

       Pros and Cons Poly-tunnels  

  • A poly-tunnel is far cheaper to build so you would have a larger covered space for you money.  
  • Poly-tunnels will get a lot hotter in the summer and far more humid, which could increase the chance of getting more diseases.
  • They can be blown away by strong winds, which is why the frame should be attached to the ground properly.
  •  Covers need to be replaced every 5 years.