Do a search for polytunnels on the computer and you’ll see that there is plenty of choice out there! Tunnels come in different shapes and sizes; they cost different amounts accordingly and most people want to get the best structure they can, for the best price.
Consider what shape you want – a hooped tunnel, a geodesic dome or a greenhouse-style pitched roof? Some hooped frames have straight sides, so more use can be made of the edges of beds inside. A lot of this is down to personal preference and the suitability of the site. A short, wide tunnel will fit some sites better than a long, narrow one.
Then there are issues like the strength of the structure, especially if the site is buffeted by strong winds. Some frames are made of stronger steel, and base rails or anchor plates can help give more stability. Horizontal bracing bars across each hoop are also good in windy conditions and they are ideal for hanging things off, or for fixing shelves to. And it is worth noting that if polythene is fitted to a base rail rather than being buried, it is easier to replace.
There is also the choice of cover. Some structures have the option of rolling the polythene up along the sides to provide extra ventilation; a mesh screen covers the opening sections. There’s polythene that will last at least four years, or five years, or more. There is bubble polythene for extra insulation (this also performs well in exposed sites) and a milky-coloured one to reduce the effects of too much sun. Some polythene reduces the amount of condensation and hence reduces ‘drip’ when you are working inside.
Bubble polythene gives extra strength for exposed sites (Keder)
Any extras cost more, but they can be well worth it. Don’t rush the decision: take all the time that you need to make the right choice.
A roller simplifies side opening (Haygrove)
Important things to consider when buying
• Buy from a reputable supplier. Look at websites and ask around before making a choice.
• Choose a frame that is strong enough for the site.
• Get the strongest, longest-lasting polythene you can afford. Replacing polythene is a big job.
• Choose large enough doors to adequately ventilate the space.
• Look at strong doors and catches: buy them, or make them if you know how.
• Look at things like anti-fog polythene, which reduces the amount of condensation inside the polytunnel.
• Anti hot-spot tape is good around joints in the frame, which might snag or tear the polythene. Personally, I don’t think it’s worth putting it over the entire frame. I have a tunnel where polythene is still intact after sixteen years of direct contact with the galvanized hoops.
• Always buy a big fat roll of repair tape at the same time as buying the polytunnel.
Large polytunnels need effective ventilation (Keder)