Building your polytunnel…
We thought we’d put together a few tips and things to consider on the big build day!
Polytunnel Position.
OK, first thing to point out to anyone as absent-minded as I can be is to make sure you position the tunnel where it will get a good amount of light. Let the tunnel bask and don’t place within the range of sprawling shadows and the like.
Second, although polytunnels stand-up to wind without problem when properly secured, it’s a good idea building near to some sort of wind-break if you have the option (think trees, sheds, walls etc, but don’t obscure light!). This will help take big gusts of wind down a peg or two and ensure your tunnel lasts as long as possible.
Next, it won’t be raining in your polytunnel unless you have a leak (or it’s upside-down!), so try building near to your water source to avoid any unnecessary work (it’s the worst kind of work),
It’s a good idea to think of the route you might take to the tunnel both on foot and with a barrow/trolley etc. A direct route with no trampling of beds is what you are after.
Finally, remember that on a wet day, a polytunnel is a great place to potter around in the dry and warm, so build near enough to your door (if erecting at home) that you won’t get wet walking to it in the first place! Click here to see the Bau Outdoors Polytunnels...
Decisions…
When it comes to building your tunnel, most are simple enough in themselves, but what you need to consider is the way you are going to secure the tunnel to the ground. This is the most important element bay far, as with poor attention here, your tunnel is basically a big kite – believe us, we know if a few that have taken off!!
There are two main methods of securing your tunnel. The first is ‘trenching-in’, which as the name suggest, involves the digging of a trench around the perimeter of the tunnel, where the polythene sides are buried. The second method involves using a length of material (a scaffold plank for example) and placing the material over the polythene edges to weight them down to the floor.
We won’t bore you with a big list of pros/cons, but in our view, the best way (as is so often the case) is the harder way! It’s not hard really, but trenching-in your tunnel obviously involves a bit of digging, but as a keen gardener, you’ll be in your element anyway and the method offers a more secure solution we’d suggest.
The second method is a bit quicker and it’s probably easier to tension the tunnel, but by the time you factor in finding something to run along the sides and bring it home (or to the allotment), you’ll have used-up the time advantage anyway!
The Building
First off, lay all your bit’s out on the floor in a kind of flat-polytunnel style. Make sure you have everything required and you can see where the footprint of the structure will sit.
Put the tunnel frame together and take a tape-measure to ensure you get everything square and equidistant etc (the covers on many tunnels are tailored specifically for the frame, so it’s essential to get the frame square).
When you are happy with the frame position, you can make sure it’s secure, then dig your trench all the way along the outside (obviously skip this if securing the alternative way). The depth of your trench should be around 25-30 cm deep to ensure a good hold on the material. Keep as close to the tunnel footprint as possible – it’s a good idea to use a string-guide for this. Remember you want the cover to flow down off the frame and straight into the ground – don’t dig the trench outside the footprint!
Tip – use ‘hot-spot’ tape. This is tape which you place over the frame at points where it touches the cover. In the heat of the summer, the frame can get hot, so a bit of this tape can help protect the cover and make it last longer.
Tip – if your tunnel is one that slots together like a tent frame etc, place some gaffer tape or similar round the joins. You may see points where a zip-tie or some wire might add a bit more strength. Anything simple you can do to make the structure stronger is time well spent.
Tip – remember you need to secure the cover, so if doing the job over two days, this is a good break-point. You don’t want to leave the job overnight with a half-secured cover!
Pull your cover over the frame gently – best to have ladders and a friend or two for this. Don’t struggle and pull too hard – you should not need to and will end-up ripping your cover! Move the cover around a bit and let it settle in it’s natural position. Now you can think about burying the cover in your trench to secure it. It’s a good idea to pin the cover down in the trench with a few old tent pegs/stakes to ensure your tension remains while you are busy filling-in the trench. You can improvise and use a few rocks/bricks etc – whatever you can find – all you are doing is making sure your plastic is held as fast as possible in the ground.
Tip – when you have buried the tunnel sides, stomp the soil around the outside down and make sure the cover is really secure. It’s a great idea to pile a few rocks around the outside edge too in order to hold fast and avoid soil washing away etc.
If you are going for securing method number two, after the cover has been pulled over the frame, you will have cover edges outside the frame to secure. As mentioned, what you use is not too important, so long as it is long and can be further weighed-down with rocks (or similar) to make sure the wind can’t grab the tunnel. Any holes where the wind can get in will put extra strain on your tunnel structure – not to mention plants inside, so be vigilant here!
Tip – final tip would be to stake the tunnel frame into the ground where possible form inside. Not essential, but remember that the structure is strengthened by these little touches and this is the time to fit them in.
Hope this little guide helps out with building your polytunnel. No doubt we have missed bits, but we’ll add to it as we go! Have a look round the site for tips from Bau Outdoors members – a problem shared….
Bau Outdoor Polytunnel
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