Salting hay — sprinkling salt over each layer of bales as they go into the barn — is one of the oldest habits for hay that went up a little tough. It feels like cheap insurance, and plenty of farmers swear by it. The evidence is narrower: at the amounts farmers actually use, salt does not reliably stop mold or heating, and it cannot make wet hay safe to store. In a controlled Swiss trial, a 1% salt dose performed about as badly as no treatment at all.
Quick answer: Salt slows mold only at very high doses. In an Agroscope lab trial, hay with 1% salt (about 20 lb per ton) heated, molded and lost dry matter much like untreated hay; 5% salt (100 lb per ton) worked but pushed sodium past feeding guidelines. The rates farmers describe are closer to 2 lb per ton. Test moisture, use a calibrated preservative or wrap wet hay as baleage, and monitor bale temperatures.
This guide is for hay producers deciding what to do with marginal bales, and for buyers who find salt crystals in a load. It is not a ration or veterinary recommendation. XES manufactures bale net wrap and has not run its own salting trial; we compare archived farmer discussions with published research and Extension guidance.
Why farmers salt hay
The routine is simple. Small square bales go into the mow a layer at a time, often stacked cut side up. Someone broadcasts salt across the layer, and the next layer goes on top. Some farms salted only the top layers. A Q&A answer in The Horse explains the logic: warm, moist air from sweating bales rises through the stack, and some of it condenses on the cooler upper bales.
Farmers give four reasons for the habit: salt draws out moisture, prevents mold, lowers the fire risk and makes animals eat the hay better. Some long-time users are careful about what they claim:
"I don't think it will replace preservative for higher moisture baling as a whole, but can be better than nothing."
— OhioHay, HayTalk thread 11443
"Does it help cure hay I have no idea…just some cheap insurance I can afford 400 lbs of salt for 6000 bales."
— Farmerbrown2, HayTalk thread 79162
Others who grew up doing it are blunter about what the salt was really for:
"They'd toss 50 lbs or so into 25 tons of hay. It help[s] them sleep at night and it helps the animals like less than perfect hay."
— slowzuki, HayTalk thread 17596
What a controlled salting hay trial found
Forum stories cannot settle the question, because nobody kept unsalted bales of the same hay for comparison. A controlled test did. In 2005, Ueli Wyss of Agroscope Liebefeld-Posieux, a Swiss federal research station, published a trial of livestock salt on moist hay in Agrarforschung. Swiss organic farms and suppliers of milk for certain cheeses cannot use chemical preservatives, so salt was a practical question there.
First-cut hay was remoistened to 73.4% and 78.2% dry matter — about 26.6% and 21.8% moisture — and stored for 30 days in small laboratory containers with temperature logged every 30 minutes. Each treatment was run twice: no additive, 1% salt, 5% salt, and a buffered propionic acid preservative as a positive control. The researchers note the acid was dosed below the manufacturer’s recommendation, so its result understates a properly applied product.
| Treatment | Dry-matter loss, hay at ~26.6% moisture | Dry-matter loss, hay at ~21.8% moisture | Mold at the end |
|---|---|---|---|
| No additive | 33.2% | 13.9% | Totally moldy at both moistures |
| 1% salt (about 20 lb per ton) | 22.0% | 9.6% | Totally moldy in the wetter hay; moldy in the center of the drier hay |
| 5% salt (about 100 lb per ton) | 3.8% | 1.5% | Moldy in the center only |
| Buffered propionic acid, below label rate | 13.2% | 4.5% | Moldy in the center only |
Statistically, the 1% salt result could not be separated from untreated hay at either moisture, and both heated much more than the 5% salt and acid treatments. Wyss summarized it bluntly: the 1% salt variant was “practically as bad” as the variant without additive. The 5% dose worked, but the treated hay’s sodium exceeded feeding recommendations, so he concluded that dose cannot be recommended for livestock feed. The trial also questioned how much salt would actually stay on hay applied in the field or survive to the feed bunk.
Two limits matter. These were half-kilogram samples in small containers, not field bales, and the trial ran for a month. The direction of the result is still consistent with Extension advice. University of Maine Cooperative Extension professor Richard Kersbergen told the Bangor Daily News in July 2025 that he knows of no university research recommending salt to keep hay from molding, that an effective amount would affect whether animals eat the hay, and that salt is “really not antimicrobial.”
The dose problem: farm salting rates vs. the trial
Put the farm rates on the same scale as the trial and the gap is obvious. The table converts each rate to salt per ton of hay and per 50-pound small square bale. The farm examples are the amounts quoted above, not measured applications.
| Rate | Salt per ton of hay | Salt per 50-lb bale | What we know about it |
|---|---|---|---|
| Farm example: 50 lb into 25 tons | 2 lb (0.1%) | About 0.8 oz | One-tenth of the dose that failed |
| Farm example: 400 lb for 6,000 bales | About 2.7 lb, if bales weigh 50 lb | About 1.1 oz | Roughly one-eighth of the dose that failed |
| Trial: 1% salt | 20 lb | 8 oz | Heated, molded and lost dry matter much like untreated hay |
| Trial: 5% salt | 100 lb | 40 oz (2.5 lb) | Little heating, but too much sodium for routine feeding |
In other words, a typical farm application puts about an ounce of salt on a 50-pound bale. Matching the dose that failed would take half a pound per bale; matching the dose that worked would take about 2.5 pounds. The Swiss paper also cites an older Austrian recommendation of 3 to 20 kilograms of salt per tonne of hay, roughly 6 to 40 pounds per US ton. The 1% test sat in the middle of that range and still failed.
Why sprinkled salt can’t reach the problem
Salt does pull water toward itself, and at high enough concentrations it lowers the water available to microbes — that is why it is used in curing meat and making sauerkraut. Hay is different. The moisture that drives heating sits inside the bale, in stems and tight flakes, while broadcast salt lands on a few outside surfaces. The Horse answer cited above says surface-broadcast salt “was not terribly effective” because it could not be distributed thoroughly through the bales. A grower raised on the practice put it this way:
"Tossing it in on the layers, you can't distribute it evenly enough to each part of each bale to stop bales from spoiling, it just won't happen"
— slowzuki, HayTalk thread 79162
The trial even undercut the “draws moisture out” idea. Spoilage produces water, so the wetter untreated and 1% salt samples finished the month with lower dry matter than they started: 64.4% and 68.6%, down from 73.4%. Only the 5% salt and acid samples held or gained.
Why do so many farmers believe it works? In these discussions, salt was usually reserved for hay that was only a little tough, and nobody kept an untreated comparison. Another HayTalk member made that point in the same discussion:
"Unless you had bales left untreated the same time you treated some (controls), you can't make any claim the salt worked."
— Hayjosh, HayTalk thread 79162
Palatability can also hide a problem. Livestock like salt, so salted hay can be eaten readily even when it has lost quality:
"The salt really just makes bad hay test good to the animals"
— Rodney R, HayTalk thread 11443
Salting hay claims, checked
| Claim | What the evidence shows |
|---|---|
| “Salt keeps hay from molding” | Only at 5% in a lab trial. At 1%, the wetter hay molded completely, like untreated hay. |
| “Salt draws the moisture out” | Not at practical rates. In the wetter hay, the spoiling 1% salt samples finished wetter than they started. |
| “Salt prevents barn fires” | No evidence it does. The 1% salt samples heated much like untreated hay, and Extension advice relies on safe baling moisture and temperature monitoring instead. |
| “Animals eat salted hay better” | Plausible and widely reported, but that can mask poor hay. Both trial doses put sodium above feeding recommendations. |
| “It’s cheap insurance” | The salt is cheap; the risk is storing hay you would otherwise treat, wrap or monitor. |
What to do with tough hay instead
Work through these steps in order. Each links to a deeper guide, so this page does not repeat them.
- Measure moisture correctly. A single probe reading in the wrong spot misleads; see how to measure post-baling moisture in does hay sweat after baling?
- Give it more drying time if the weather allows. Tedding and raking decisions are covered in how to make dry hay faster.
- Apply a calibrated preservative at the baler for hay a few points too wet. Our hay preservative guide compares buffered acid and dry products.
- Wrap it as baleage when it is too wet for preservative. See wrapping wet hay.
- Separate and monitor marginal bales. Use the temperature thresholds in hay bale heating and fire prevention.
Round-bale producers should start with our moisture targets for net-wrapped bales. Net wrap protects a dry bale; like salt, it cannot dry a wet one.
If you still salt hay: five ground rules
- Treat salted bales as untreated for every moisture and temperature decision.
- Use clean, feed-grade salt and record which lots received it.
-
Tell buyers. Salt crystals surprise people who don’t expect them, as one horse-hay buyer described:
We noticed white crystals coming from a bale and called the guy we bought it from.
(HayTalk thread 17596) - Account for the sodium and keep fresh water available. South Dakota State University Extension warns that salt toxicity can follow high salt intake by unacclimated animals or water deprivation.
- Organic or contract hay: ask first. Confirm any additive with your certifier or buyer before using it; our organic hay certification guide explains why records matter.
Frequently asked questions
Does salting hay prevent mold?
Not at the rates farmers usually use. In an Agroscope lab trial, hay treated with 1% salt, about 20 pounds per ton, molded, heated and lost dry matter much like untreated hay. Only 5% salt worked, and that much sodium exceeded feeding guidelines. The rates farmers describe are closer to 2 pounds per ton.
How much salt do you put on hay?
Farmers report anything from about 2 pounds per ton to a handful per few bales, usually broadcast between layers. Those amounts are roughly a tenth of the 1% dose that failed in controlled testing. No research-backed rate makes wet hay safe, so treat salt as a habit, not a preservative.
Does salt prevent hay fires?
No. Heating comes from plant respiration and microbes inside damp bales, and broadcast salt reaches little of that hay. In the Swiss trial, hay with 1% salt heated much like untreated hay. Bale at a safe moisture, use a preservative or wrap, and monitor temperatures in any marginal stack.
Is salted hay safe for horses and cattle?
Usually, if the hay is otherwise sound and animals always have fresh water. Salt adds sodium, and South Dakota State University Extension warns that high salt intake or water deprivation can cause salt toxicity. Tell buyers the hay was salted, and never let salt hide mold, heating or dust.
What can I use instead of salt on wet hay?
Measure moisture first. For hay a few points too wet, a buffered propionic acid preservative applied evenly at the baler is a well-tested option. Wetter hay is better wrapped as baleage. Whatever you choose, stack marginal bales separately and check their temperature for the first several weeks.
The bottom line on salting hay
Salting hay is a tradition, not a preservative. At farm rates it adds flavor and peace of mind, not protection; at rates that protect, it adds too much sodium to feed routinely. Bale at the right moisture, treat or wrap what you cannot dry, and watch marginal stacks closely. When the hay is dry and ready, XES bale net wrap helps keep the bales you made tight and easy to handle.
Research note: We read five complete archived HayTalk discussions about salting hay (54 captured posts) and salting comments in 11 other forum threads, then checked the linked research, Extension and news sources on October 6, 2026. The Swiss trial figures come from the full German-language paper (Agrarforschung 12(10): 478–483, 2005). Per-bale conversions are our arithmetic, assuming 50-pound bales and a 2,000-pound ton. Post counts include questions and replies; they are not counts of farms or trials.
Featured photograph: Hay bales and 19th century barn in Champoeg State Heritage Area, Rick Obst, licensed under CC BY 2.0, via Wikimedia Commons. Small square bales beside a historic Oregon barn; it is not a salting demonstration or an XES farm. Image unchanged apart from display resizing.
