The metal framework of a polytunnel (high tunnel) should last for decades, but the cover needs to be replaced every five years. With proper care they can last much longer, so here are the ground rules for caring for your cover.
Buy a quality cover
You get what you pay for, so buy your cover from a reputable manufacturer. You can certainly buy cheap tunnel kits on EBay, but we don’t recommend it: the steelwork is usually thinner and often has rough spots that will reduce the lifetime of the cover, and – worse – the plastic can be thinner too. We’ve even seen one seller respond to the question ‘are your covers UV-stabilised?’ with a curt ‘the item is sold as seen’ which obviously meant ‘don’t know, don’t care’. Without UV stabilisers, a cover will be brittle by the end of its first summer, and unlikely to see the winter out.
Get a tight fit
Make sure the cover is as tight as a drum when you fit it to the frame. This isn’t just about looks, because a tight cover flexes less in the wind than a saggy one. Less movement means less rubbing on doorframes and steelwork, which means a longer life. Likewise, if it’s a new installation, put the tunnel broadside to the prevailing wind if you possibly can so that the wind isn’t constantly trying to blow the tunnel up like a balloon.
Make repairs quickly
Don’t delay when damage occurs: fix it fast. A tiny hole from the end of a bamboo cane might not look like much, but your cover is only as strong as its weakest point: in a storm that hole can turn into a rip in no time at all, and if the wind really gets a hold it can take a damaged cover clean off. Holes that you don’t see are just as dangerous as the ones you do: this means you have to check your cover carefully (especially around the door frames where wear and tear tends to show first) a couple of times a year, and most importantly in the autumn.
If you have cover repair tape (available from all polytunnel retailers) to hand, repairing a small hole is a two minute job: just smooth a piece of it down on each side of the film. For larger holes or small rips, place two pieces at right angles to each other to form an X shape, again on both sides of the film.
Take care with your cover
Don’t ask too much of the plastic film, especially as it gets older and less flexible. Polytunnel plastic is strong stuff but there’s a limit to what it can put up with, and it gets less strong every year until it eventually gives up. Be firm but gentle when cleaning your cover, and don’t even consider using a pressure washer.
Bamboo canes are risky things to have around in the tunnel, especially when you’re pulling them up at the end of the summer. When the soil finally lets go it’s very difficult not to jab them upwards, and – pop! – you have a hole on the top of the tunnel that can really only be patched on the inside. Keep pointy things to a minimum in the tunnel, and if you must have canes, keep them short. For tall plants, think about using growing strings instead.
Be careful with visitors
Cats are the most common culprits of cover damage because they have claws and love to climb, but other animals can cause damage too. If a critter decides your tunnel is fair game, your only option is to try to ban it from the whole tunnel area. The easiest way to do this for earthbound pests is to put a mulch of chopped holly leaves or similar prickly foliage all the way round your polytunnel. Birds are trickier, but thankfully problems are rare: make your polytunnel less attractive by providing alternative places to perch nearby, such as shrubs and trees.
Adults aren’t the only ones to appreciate the versatility of tunnels. Children will quickly realise that they are not only the driest place in a downpour, but that they make excellent spaceships, playhouses and soccer goals. Your own children may be extremely careful and appreciate the tunnel for what it is, but their visiting friends will not. Set clear rules about who is allowed in the tunnel when you’re not around!
Watch the weather
Wind and rain are no problem for a polytunnel provided the wind isn’t being funnelled in through a doorway, but some kinds of snow can build up to an alarming thickness before they slide off. Crop bars and storm braces both improve the structural strength of the frame, but it’s a really good idea not to let too much snow build up on the tunnel. A tap with the back of your hand from the inside is usually enough to dislodge snow, but if not use a soft yard brush to pull it off the sides of the tunnel. Once the light gets into the tunnel things should warm up enough to take care of any snow left on the top for you.