How to make polythene last more than a decade
• Buy the best-grade polythene available.
• Plant a hedge, put up a fence or use strong netting to create a windbreak. This doesn’t have to be so high that it shades the polytunnel, but it does have to be high enough to deflect strong winds.
• Buy a roll of repair tape at the same time as buying the polytunnel. Use this to repair small holes and rips before they become large ones.
• Check the polythene regularly.
• Remove any overhanging branches before they fall and damage the polythene. A tree surgeon might be needed to do this.
• If a strong wind blows in at one door of the polytunnel, either close it or open another door so that the wind can get out again.
How to repair rips and holes
Even new polythene can tear or be punctured, but if you repair a small hole straight away it won’t develop into a rip. Repair tape, which looks like a giant roll of Sellotape, will do a much more effective job than duck tape (also called duct tape), parcel tape or masking tape. Buy the broadest roll available; it might seem expensive, but one roll will last a long time. Check the polythene cover every few weeks, especially through the winter months and after strong winds. If a sharp stick or fork pokes a hole, repair it straight away. If you catch damage while it is still small, you can do a good repair job in six easy steps:
1. Wash the polythene inside and out around the tear. Use soapy water for this (washing-up liquid works well) and a kitchen sponge with a mild abrasive pad to remove any film of dirt.
2. Dry the polythene with a piece of kitchen roll and leave it to air dry completely before applying a patch. If in a hurry, use a hair dryer.
3. Cut a length of tape that will cover the rip with a minimum of 2cm/¾in overlap all around.
4. Cut the points off the four corners of the repair patch. This makes the edge less likely to lift and peel away.
5. Enlist a helper to support the back of the polythene. Apply firm steady pressure while pressing the patch into place. Remove any air bubbles by squeezing them toward an edge of the patch. Make sure you achieve a tight bond all around.
6. Swap sides and repeat, so that you patch the damage both inside and out.
You can repair larger rips using the same principle, but you may need several helpers to support the polythene.
1. Add some Citrox (or Citricidal), plus a squirt of environmentally safe washing-up liquid, to a bucket or bowl of warm water.
2. Start with the outside and, using a small brush, scrub out any folds that might harbour pests and diseases.
3. Next use a long-handled broom with soft bristles to scrub down the polythene. Make sure the brush is the right size to dip into the bucket or bowl. Refill the bucket with soapy water as often as necessary.
4. To reach over the top of a tall structure, use a soft brush head fitted on to the end of a hosepipe – these are often used for washing cars. You can extend the length of ‘reach’ by taping the brush to a long smooth stick or a telescopic handle. Take care that there are no protruding parts that might tear the polythene. Clear water running through the pipe will be perfectly fine for cleaning over the top – just scrub a little with the brush.
5. Use a hosepipe to rinse the polythene with clear water.
6. Repeat the process on the inside of the tunnel, but remember to wear a waterproof jacket with the hood up! The long-handled brush should reach to the top, but it will drip.
7. Give any growing plants a quick squirt of clean water.
8. Stand back to admire the effect, but also to check for any bits that you have missed.
Repairing doors
Galvanized metal doors will last for years, although they might need re-covering with polythene. Wooden ones might fall apart and rot. If a new wooden door is needed, it isn’t hard to make one. Don’t use heavy timber, as this might pull on the frame (47mm x 22mm is fine). Do use diagonal bracing so that the door doesn’t twist or slip out of shape. A diagonal brace can be as simple as a piece of timber running from one corner to the diagonally opposite one. Make sure the corners are square before screwing the brace in place. Alternatively, triangles of plywood can be screwed across each corner.
Check hinges to see if these need to be replaced. Screws can pull loose from the door frame.
Check the door catch at the same time. If it’s loose, the door might blow open in a strong wind.