This isn't about when to cut or how to prepare your sward. It's about what happens once the grass is going into the pit — and specifically, how to cover and seal it in a way that drives fermentation, eliminates waste, and makes life easier on the farm.
We recently carried out a trial on the Salesian College Farm in Pallaskenry with a clear goal: zero waste and maximum silage quality. No tyres were used on the pit at any point — gravel bags only. The covering system was a single sheet of Agvance oxygen barrier film laid directly on the silage, followed by a standard gauge black polythene sheet, with a woven silage cover on top. The results were impeccable. The set-up ticked both boxes we were aiming for: significantly improved preservation and a major reduction in labour at both covering and uncovering.
Here's why it works.
-Compaction: Remove as Much Oxygen as Possible
Before any sheet goes on the pit, the single most important thing you can do is compact well. The principle is straightforward: the more oxygen you drive out of the clamp during filling, the better your silage will ferment — and the faster fermentation kicks in once the pit is sealed.
Fermentation is an anaerobic process. It can't begin properly while oxygen remains in the clamp. Every air pocket you leave behind delays the drop in pH, extends the window during which aerobic spoilage can occur, and reduces the quality of what you'll be feeding out come winter. Roll in thin layers, roll continuously, and roll with the heaviest machine you have. Compaction and sealing work together — there's no point in a perfect cover over a poorly compacted pit.
-Sealing: The Covering System That Delivers Zero Waste
Once compaction is done and the final load is in, sealing is everything. The system we used at the Salesian College Farm in Pallaskenry is built around three layers, each doing a specific job.
Layer 1: Agvance Oxygen Barrier Film The first sheet to go on the silage face is the most important. An oxygen barrier film is specifically engineered to prevent oxygen transmission through the material itself. It's a fundamentally different product from other films on the market.
Some farms use cling film-style wraps as their first layer. These are generally less effective at keeping oxygen out than standard black polythene — they look similar but they're not performing the same job. A true oxygen barrier film sits at the other end of the scale entirely: it blocks over 100 times more oxygen than standard black plastic. One easy way to tell the difference is to pull the material. A genuine oxygen barrier film will stretch significantly without tearing — it has real elasticity and strength. That stretch is what allows it to conform tightly to the silage surface, eliminating the small gaps and air pockets that cause spoilage at the top and shoulders of the pit.
The oxygen barrier goes on first, tight to the silage face, and it does the heavy lifting when it comes to fermentation quality.
Layer 2: Standard Black Polythene Sheet Black polythene is a well-established part of silage covering, and in a layered system it plays a valuable role. Laid over the oxygen barrier, it adds a second layer of physical protection and reinforces the barrier against oxygen ingress from above. Between the oxygen barrier below and the woven cover on top, it contributes to a robust, well-protected clamp.
Layer 3: Woven Silage Cover. The woven cover goes on top and holds the whole system in place. Because it has real structural weight and lies flat under load, you need far fewer bags on top compared to lighter film covers alone — the cover does much of the work itself. It's completely bird-proof, which is a more significant issue than many farms realise: bird and animal damage to covers is a well-documented cause of localised spoilage in otherwise well-sealed pits.
The woven cover also makes uncovering at feeding time considerably more straightforward. Rather than dealing with multiple sheets, scattered tyres, and improvised weights, you're removing one structured cover. That's a real time saving over the course of a feeding season, and it was a central part of what we set out to demonstrate at the Salesian College Farm in Pallaskenry.
Built to last several seasons, the cost per cut comes down year on year.
-Weighting and Sealing: Gravel Bags The covering system is only as good as its seal at the perimeter, and how well the cover is held down across the full surface. Edges that lift — even slightly — allow oxygen to work its way underneath, and the damage tends to spread inward from there.
One of the best ways to seal and weight a pit is gravel bags. At the Salesian College Farm in Pallaskenry, bags were placed edge to edge all the way around the perimeter of the cover, creating a continuous, unbroken seal with no gaps. Rows of bags were also run across the full width of the pit every 4–5 metres, with a row down the centre of the pit as well. This keeps the cover pressed flat and prevents any lifting or movement across the entire surface, not just at the edges.
No tyres were used at any point. The bags handled everything, and the reduction in labour alone — no sourcing, stacking, or shifting tyres — made the switch worthwhile before the preservation benefits were even counted.
If you don't have gravel bags, tyres can still be used on top of the woven cover. Because the woven cover lies flat and holds its position far better than a standard black polythene sheet on its own, you'll need noticeably fewer tyres than you would if polythene were your top layer. It's a practical middle ground if you're making the transition gradually.
-The Full System
| Layer | Product | Purpose |
| 1st — on the silage face |
Agvance oxygen barrier film | Blocks oxygen at the source, conforms tightly to the silage surface |
| 2nd — over the barrier |
Standard black polythene sheet | Added physical protection, secondary layer against oxygen ingress |
| 3rd — on top |
Woven silage cover | Bird-proof surface protection, holds system in place, easier uncovering |
| Edges + surface | Gravel bags edge to edge, rows every 4–5m across and down the centre | Continuous perimeter seal, full surface held flat, no tyres needed |
This is the system that delivered zero waste and maximum quality at the Salesian College Farm in Pallaskenry. The goal was to show that better preservation and less labour aren't a trade-off — with the right set-up, you get both.
*Agvance oxygen barrier film, woven silage covers and gravel bags (filled and delivered to your yard) are all available from Animal Farmacy — online at animalfarmacy.ie or by phone.*