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Why a Small Tear Deserves a Proper Repair

A pinhole in polytunnel film is never just a pinhole. The moment wind finds a gap, it works its way underneath and starts lifting the edge, and every gust widens the damage a little further. A tear the size of a thumbnail in March can be a flapping, metre-long split by June if it is left alone.

There are other reasons to act quickly. Water finds its way through the opening and drips onto foliage below, which is a recipe for botrytis and other rots in a warm, humid tunnel. Light transmission drops as the film ripples and lifts, and the tension across the whole cover becomes uneven, which puts extra strain on the hoops and the ground rails. Repairing a tear takes fifteen minutes; replacing a cover takes a full weekend and a considerable amount of money. Small repairs really do pay for themselves.

What You Will Need

Gather everything before you climb up, so you are not clambering down a ladder every few minutes. A decent kit is inexpensive and will last years.

• UV-stabilised polythene repair tape — the clear or white greenhouse type, not duct tape and not gaffer tape. Both of those go brittle and leave a sticky residue that nothing will ever stick to again.
• Mild soapy water and a soft cloth or sponge, plus a clean, dry lint-free cloth.
• Isopropyl alcohol or a similar evaporating cleaner for the final wipe on greasy or algae-covered film.
• Sharp scissors for cutting tape and rounding patch corners.
• A helper if the tear is above shoulder height — one person to hold the film flat while the other applies tape makes a far neater job.
• Steps or a stable platform, never a bucket or an upturned crate.

Cleaning the Damaged Area First

Adhesive will not grip dirty polythene, so cleaning is the step that decides whether the repair lasts a season or a fortnight. Work on a dry day, and ideally in the early morning or late afternoon when the film is neither rigid with cold nor stretched tight by midday heat.

Begin by gently pressing the torn edges back into their original position so you can see the full extent of the damage. Wipe a generous area around the tear — at least 10 cm in every direction — with the mild soapy water to remove dust, pollen and the green algae film that builds up on older covers. Rinse with clean water and then wipe the whole area again with isopropyl alcohol. Allow it to dry completely; even a faint damp patch will trap moisture and weaken the bond.

Trim any ragged, curled or stretched edges with scissors. A clean, straight edge sits flatter and takes tape far better than a frayed one.

Applying Tape on Both Sides

The trick with polytunnel repairs is to sandwich the film. A patch on one side only will always peel, because the film moves beneath it in the wind. Tape both faces and the repair becomes part of the structure.

On the inside, cut a piece of tape that overlaps the tear by roughly 5 cm on every side. Round off the corners with your scissors — square corners catch the wind and start lifting. Press it on firmly, working from the centre outwards with your thumb or a soft cloth to push out any air bubbles.

Now go outside and repeat the process, positioning the outer patch so that it overlaps the inner one but does not sit exactly on top of it. Staggering the two layers spreads the load nicely. For a long vertical split, run the tape along the length of the tear rather than across it, and add a short horizontal strip at each end to stop the split travelling further.

Do not stretch the tape as you apply it. Lay it down relaxed, and let it sit flush with the film.

Checking the Tension Afterwards

A repair is only as good as the tension around it. If the cover is slack, it will flap, and flapping film will tear again beside the patch within weeks.

Check the ratchets or tensioning system at the end of the tunnel first. Tighten gradually — a quarter turn at a time, walking the length of the tunnel between adjustments — rather than cranking one side hard. You are aiming for a firm, drum-like surface with no hollows between the hoops.

Walk along the sides and check that the film is still properly buried in the ground trench or clamped to the base rail, and that crop bars and side rails are all in place and doing their job. If the tear has appeared right at a rail or hoop, add a second patch on the inside of that contact point, because that is where the film rubs and fails.

Keeping Repairs Sound Through the Season

Once it is taped, make a habit of glancing at the repair whenever you are in the tunnel. A patch that begins to lift at one corner can be pressed back down or edged with a fresh strip before it fails completely.

After any serious gale, do a full lap of the structure. Storm damage rarely announces itself — you will often find three or four small splits along the ridge or on the windward side that were not there the day before. Deal with them while they are still small.

Keep a roll of repair tape, scissors and a clean cloth in the potting shed so a repair never has to wait for a shopping trip. And be realistic about older covers: if the film has gone brittle, chalky or cracked across whole panels, patching is only a holding measure, and budgeting for a replacement cover is the sensible next step.