Why This Summer Has Challenged Even the Best Silage Makers

What the 2026 heatwave can teach dairy farmers about fermentation, forage quality and the science behind better silage

Across many dairy farming areas this summer, grass has presented an unusual challenge.

Traditionally, silage-making discussions tend to focus on crops being too wet. This year, in many areas, the concern has been the exact opposite. Extended periods of hot, dry weather have seen grass wilt exceptionally quickly, with some producers reporting crops reaching target dry matter levels in a matter of hours rather than days.

The consequences have been noticeable. There are reports of bales being opened only weeks after wrapping and showing little evidence of fermentation. In some cases, the crop appears more like preserved dry grass than true silage.

Whilst extreme weather undoubtedly plays its part, these situations also provide an opportunity to revisit an important question:

What actually turns grass into silage?

Understanding that process helps explain not only why this year’s conditions have been challenging, but also why some silage analyses consistently outperform others.

Silage Is Not Preserved Because It Is Wrapped

A common misconception is that wrapping a bale or covering a clamp is what preserves the crop.

In reality, wrapping is only part of the process.

Silage is preserved through fermentation.

Once grass is cut, both the plant and naturally occurring microorganisms remain active. Plant respiration continues to consume sugars while bacteria begin competing for available nutrients. If oxygen is excluded quickly enough, beneficial lactic acid bacteria dominate. These bacteria convert plant sugars into lactic acid, causing the pH to fall.

As the environment becomes more acidic, spoilage organisms are unable to thrive and the crop is effectively preserved.

The key point is simple:

Silage is not preserved because it is wrapped. It is preserved because fermentation creates conditions that prevent spoilage.

Everything that happens during mowing, wilting, tedding, harvesting and storage influences the success of that biological process.

The Importance of Dry Matter

Among all the figures that appear on a forage analysis report, dry matter (DM) is arguably the most influential.

Dry matter represents the proportion of the forage that is actual feed rather than water. For high-quality dairy silage, a target of around 30–40% DM is generally considered the sweet spot for achieving good fermentation whilst maintaining intake and forage stability.

When forage is too wet, fermentation can become excessive and undesirable bacteria may flourish.

When forage becomes too dry, however, an entirely different set of problems emerges.

Very dry crops are more difficult to compact effectively, whether in a clamp or a bale. Air pockets remain trapped within the forage mass, increasing the risk of heating, mould growth and spoilage. In addition, the bacteria responsible for fermentation require moisture to function efficiently. As moisture levels fall, fermentation becomes less reliable.

This is one reason why some producers have encountered difficulties during recent heatwaves.

What might historically have required a 24-hour wilt can, under hot and windy conditions, become a 6-hour wilt. Miss the optimum window and dry matter can quickly exceed desirable levels, leaving the crop harder to preserve effectively.

The lesson is clear:

In extreme weather, farmers need to monitor crop condition rather than follow historic wilting routines.

Why Timing Matters More Than Yield

Grassland management is often a balancing act between quality and quantity.

The temptation to delay cutting for a few extra days in pursuit of additional bulk can be difficult to resist. Yet each day a grass crop remains standing beyond its optimum stage, its nutritional profile changes.

As the plant matures, stem production increases, fibre content rises and digestibility falls.

Whilst yield may continue to increase, feeding value often declines.

This relationship explains why some of the highest-performing dairy silages come from crops that appear modest in bulk but were cut at precisely the right stage of growth.

Put simply:

The best silage is usually harvested before the crop looks at its best.

That statement can feel uncomfortable when standing in front of a field with another tonne of potential yield still to come. However, dairy cows are paid through milk solids, not grass tonnage.

Understanding The Numbers That Matter

Forage analyses can often appear overwhelming.

Pages of technical data can hide the measurements that genuinely matter from a practical feeding perspective.

Three numbers deserve particular attention.

ME – The Cow’s Fuel Tank

Metabolisable Energy (ME) is effectively the amount of useful energy available to the cow.

Energy drives production.

For high-performing dairy systems, an ME greater than 11.5 MJ/kg DM is generally regarded as an excellent result.

Every improvement in forage quality reduces reliance on purchased concentrate feeds and creates greater flexibility within the ration.

When forage quality rises, feed costs often fall.

NDF – The Intake Limiter

Neutral Detergent Fibre (NDF) measures structural fibre within the crop.

As grass matures, NDF increases.

The challenge is that intake and NDF tend to move in opposite directions. As fibre rises, cows consume less forage.

This is why two crops producing similar tonnages in the field can perform very differently in the parlour.

A target below 45% NDF is generally associated with highly digestible dairy silage, whilst values above 50% often indicate a mature, stemmy crop harvested later than ideal.

For many farmers, NDF deserves far more attention than it receives.

Ash – The Hidden Cost

Ash is often overlooked but can tell an important story.

Whilst some mineral content is naturally present within forage, elevated ash levels frequently indicate soil contamination introduced during mowing, tedding or raking.

The implications extend beyond appearance.

Contamination can negatively impact fermentation, reduce palatability and affect overall silage quality.

Good cutting heights, careful machinery setup and sensible field operations remain some of the simplest and most cost-effective quality interventions available to a grassland manager. A target below 9% ash is generally desirable.

The Economics of Better Silage

Silage quality is often viewed as an agronomic issue.

In reality, it is fundamentally a business issue.

Consider two clamps.

One analyses at 10.8 MJ ME/kg DM.

The other analyses at 11.8 MJ ME/kg DM.

The numerical difference appears small on paper, yet across a winter feeding period the implications can be substantial. Higher-quality forage can reduce purchased feed requirements, support greater milk production and improve overall feed efficiency.

Viewed through this lens, silage making becomes more than a harvest operation.

It becomes one of the most significant opportunities a dairy business has to influence profitability before winter arrives.

The cheapest energy and protein fed throughout the year is often the energy and protein successfully preserved during the silage season.

Lessons From An Unusual Year

Every silage season teaches something.

This year’s weather has reinforced several important principles:

• Monitor crop condition, not the calendar.
• Monitor dry matter, not wilting time.
• Cut for quality rather than maximum bulk.
• Prioritise compaction and oxygen exclusion.
• Minimise soil contamination.
• Analyse every cut.
• Build rations from evidence, not assumptions.

Perhaps most importantly, it has reminded us that successful silage is never the result of a single decision.

It is the cumulative outcome of dozens of small decisions made before, during and after harvest.

Final Thoughts

Silage is often described as an art, but the principles underpinning success are firmly rooted in science.

The recent heatwave has highlighted how quickly conditions can change and how rapidly opportunities can be won or lost. Grass that appears ideal in the field can become difficult to ensile if moisture levels fall too far. Equally, relatively small improvements in cutting date, compaction, contamination control or crop management can deliver benefits that are felt throughout the winter.

For dairy farms, silage remains far more than winter forage.

It is one of the most important crops grown on the farm.

Understanding the science behind it is often the first step towards unlocking greater production, lower purchased feed costs and a more resilient dairy business.