Wrapping Dry Hay in Plastic: Does It Make Sense?

By the XES Netting team — bale net-wrap manufacturer · Updated August 16, 2026 · ~17 min read

“Can I just wrap my dry hay in plastic to store it outside?” is a common question, and it’s easy to see why — you have a wrapper, you have film, and you want to protect bales without building a barn. The honest answer is more nuanced than a flat yes or no: it depends on exactly how dry the hay is, what storage alternative you actually have, and whether you’re prepared to run a real baleage system rather than improvise one.

This guide walks through why plastic film and truly dry hay usually don’t mix, the one documented exception for producers without covered storage, why borderline (18–25%) hay needs a measured decision rather than a guess, and the fire, handling, and disclosure basics that apply once bales are sealed. Sources are university extension programs and a livestock diagnostician, cited by name below — not forum opinion.

Why plastic film usually doesn’t suit dry hay

Baleage works because forage sealed away from oxygen ferments: anaerobic bacteria convert plant carbohydrate into lactic acid, the pH drops, and that acidity is what preserves the bale. According to Penn State Extension, the optimal moisture for that fermentation is roughly 45–60%, with fermentation still possible — but increasingly risky — from about 30% up to 70%.

Dry hay sits well outside that window. That doesn’t mean the sugar is simply gone — cured forage still contains carbohydrate. The limiting factor is water activity: lactic-acid bacteria need enough free moisture to multiply and produce the acid that suppresses mold. A University of Georgia Extension baleage bulletin puts it directly: forage under roughly 40% moisture “will not ferment well,” and while it “can still be good feed as long as anaerobic conditions are maintained,” baling that dry “increases mold production and greatly increases storage losses.” Seal hay far below that range — down in the teens — inside an airtight film, and you get the oxygen exclusion without the acid drop that would normally keep mold in check.

Extension programs and diagnostic reports commonly describe the practical result as an outer layer of mold where sealed film contacts hay that never fermented. That’s a documented, recurring pattern — not a guaranteed outcome for every bale in every climate, since local humidity, film integrity, and exactly how dry the hay was all change the result. It’s also why “just use fewer wraps so it can breathe” isn’t a reliable fix: fewer layers mainly add pinholes that let outside moisture in without giving the bale a genuine vapor path out.

A documented exception: the University of Kentucky outdoor-wrap method

This isn’t a blanket “never.” The University of Kentucky Forage Extension Program directly answers the question “Can I wrap dry hay as an alternative to inside storage?” for producers who have no covered space at all. Quoted directly, in full:

“Some producers who have limited inside space for storing dry hay rolls have successfully wrapped dry hay for outside storage. Typically only enough plastic to cover the bale is needed, usually 2 layers with about a 20% overlap at the edges. Black plastic is recommended rather than white plastic since it is cheaper, draws heat, and helps to evaporate condensation within the bale. At the bottom, between each bale, make a vertical cut to allow for ventilation between bales. A 1-2 inch layer of white mold may develop on the outside of each bale, but any losses associated would be far less than unwrapped outside stored hay. Wrapping hay that is higher in moisture than about 20% will mold more significantly.”

Treat that for exactly what it is: one land-grant extension program’s specific, narrow method for one situation — no covered storage available, hay already at or below roughly 20% moisture, and an upfront expectation that a 1–2 inch mold layer will form. It is not a general endorsement of wrapping dry hay. The source page also carries no visible publication or revision date, so treat it as directional, source-specific guidance rather than a dated current standard — and verify that your own local humidity, film thickness, and ventilation setup behave the way the method assumes before relying on it. Documenting a storage method is not the same as certifying the resulting mold layer safe to feed (more on that next).

Never feed the moldy layer

Whether mold forms from the UKY method, from an accidental too-dry seal, or from ordinary outdoor exposure, the feeding decision is the same: don’t clear off a moldy outer layer and feed the rest without professional input. Grant Burcham, DVM, PhD, a veterinary diagnostician at Purdue University’s Heeke Animal Disease Diagnostic Laboratory, has traced listeriosis and botulism deaths in necropsies to improperly preserved forage, and mold risk carries its own species-specific pattern:

• Horses are the most sensitive common livestock species. Mississippi State University Extension notes horses can develop Recurrent Airway Obstruction (“heaves”) from moldy forage, along with colic risk.
• Pregnant and lactating animals of any species carry higher risk from moldy or mycotoxin-contaminated feed. Cattle break down some mycotoxins in the rumen, but pregnant cows remain vulnerable to mycotic abortion. Because risk varies by mycotoxin type, species, and reproductive status, don’t assume any animal — dairy or otherwise — is safe on moldy feed without professional input.
• Visual and smell checks are not a safety test. Mississippi State Extension is explicit that the only way to confirm the type and amount of mold and mycotoxin present is a diagnostic laboratory test; color and odor “might provide visual cues” but “might not provide a complete picture.”

If you’re unsure whether hay is safe to feed — wrapped or not, and regardless of how light the mold looks — the responsible next step is a call to your veterinarian or a livestock nutritionist before feeding it. A representative, professionally guided lab sample can inform that decision, but because mold and mycotoxin levels vary within a lot, no single test, sensory check, or “it looked fine on top” inspection certifies an entire heterogeneous lot free of mold or mycotoxin. Treat visible mold as a reason to hold that hay back from feeding until a professional weighs in, not a reason to test only once it looks bad enough. This guide covers storage decisions; it is not a feed-safety clearance.

Borderline hay (18–25% moisture): don’t split the difference

Roughly 18–25% moisture is the band where people most want a shortcut, and it’s exactly where guessing gets expensive. Purdue Extension gives package-specific unpreserved-storage targets, not one blanket number: 20% for small rectangular bales, 18% for large round bales, and 17% for large rectangular bales. Where 18–25% sits relative to “dry” depends on which of those you’re baling — the low end of the range sits right at the large-round target and above the large-rectangular target, but at or below the small-rectangular target; the high end is above all three. Either way, the entire 18–25% band sits well under the roughly 40% moisture University of Georgia Extension says forage needs to ferment well, so this measured range does not qualify for baleage. Baleage is a separate path only for forage that an independent moisture check places in a validated fermentation range (roughly 40%+) — it is not a fallback for hay that tests at 18–25%. In short: hay in this band is a measurement-and-package problem to solve — re-dry it, or treat it with an effective preservative applied exactly within that product’s label and your bale type’s package guidance — not a texture to guess at (“tough” or otherwise), and not a baleage candidate.

What that means in practice:

• Measure it directly, for your specific package. Moisture varies inside a bale, and the safe threshold differs by bale type and density (see the exact Purdue package targets above). Use a calibrated forage moisture tester with several readings across the bale, or a forced-air/microwave test — not a squeeze-and-guess.
• If it’s confirmed in this range, re-dry it or store it with an effective preservative labeled for that moisture range, applied at the labeled rate and within your bale type’s package guidance — follow the product label for its specific moisture ceiling, and re-test rather than assume the treatment covers any moisture level.
• Baleage is a different, separate project — not a route for hay that tested 18–25%. It only applies when an independent moisture check finds forage in the validated fermentation range (roughly 40%+, per University of Georgia Extension), and even then it requires a complete system: the right crop and carbohydrate stage, adequate bale density, rapid wrapping in a genuine oxygen-barrier film (extension sources commonly specify 6–8 layers), a puncture-inspection routine, awareness of clostridial and listerial risk, and a feed-out plan once opened. That belongs with dedicated baleage guidance, not this article.
• What this guide does not recommend is sealing 18–25% hay in film hoping for a light, informal fermentation. UGA’s ~40% boundary for reliable fermentation means hay in this band is below where that process works safely, and getting the moisture, carbohydrate, density, or seal wrong risks either a moldy bale or, at the wetter end with soil contamination, the clostridial and listerial risks described above.

Three different products, three different jobs

Part of the confusion here is that three different materials get lumped together as “wrapping”:

• Silage stretch film is engineered to be an oxygen barrier. That’s the entire point — it excludes air so anaerobic fermentation can occur. Around hay that isn’t wet enough to ferment, that same oxygen-barrier property is the problem, not the benefit.
• Breathable commercial bale covers, sleeves, and tarps are a separate product category from silage film, sold specifically for weather protection rather than fermentation. Because “breathable” and “waterproof” claims vary by manufacturer and product line, verify the specific system’s rated permeability and coverage with the maker before relying on it — don’t assume one cover or sleeve behaves like every other one.
• Net wrap is an open polyethylene mesh that binds the bale into a round shape — that’s its job. It is not a fermentation film and it is not a waterproof cover, and it does not inherently make hay “breathe,” dry hay that was baled too wet, or manage weather exposure. Its open structure lets more air and moisture through than a sealed film, but keeping rain off a bale is a job for a separate cover, tarp, shed, or well-drained site — not a property of the net wrap itself. Hay still has to be cured to a safe moisture before baling, regardless of what covers it afterward.

What to do with genuinely dry hay

For hay confirmed dry by direct measurement, the approach extension programs and commercial operations both rely on is net wrap to bind the bale’s shape, paired with a separate cover, tarp, or shed to manage weather — not an airtight film seal:

• Net wrap plus a tarp or purpose-built bale cover over the stack handles most outdoor storage situations without creating an airtight seal against forage that isn’t fermenting.
• A shed, hoop building, or other roofed storage is the strongest option where it’s available — it removes direct rain and sun exposure rather than managing it after the fact.
• Site and stacking still matter, independent of the wrap choice. Bales set directly on bare ground can wick moisture from below regardless of what’s wrapped around them, and a well-drained, crowned site reduces that risk. Specific stacking details — pallets, dunnage, row spacing and orientation — vary by operation, climate, and bale type; check with your local extension office for site-specific guidance rather than a one-size-fits-all rule.

Fire risk when moisture is misjudged

Wrapping decisions aside, misjudging moisture at baling carries its own hazard: heating and, in the worst case, spontaneous combustion. North Dakota State University Extension notes hay becomes a fire hazard at roughly 20% moisture or higher in small bales, and above about 18% in large square or round bales, and that hay fires usually occur within six weeks of baling — so monitoring needs to run for weeks, not days.

Once a bale is in storage, the actionable reference is a temperature ladder. Purdue Extension, citing the Natural Resource, Agriculture, and Engineering Service (NRAES-18), lays it out this way:

Internal temperature	What to do
125°F or lower	Normal range, but hay can still heat later in the six-week window — continue at-risk monitoring rather than stopping checks.
150°F	Entering the danger zone — check temperature twice daily. Separate stacked bales or increase airflow only if it can be done safely and doesn’t conflict with fire-service direction.
160°F	Danger zone — check every couple of hours. Continue trying to increase airflow only if it remains safe to do so and is consistent with fire-service direction.
175°F	Hot spots or fire pockets likely. Stop air movement around the hay, don’t move it yourself, and call the fire department immediately.
190°F	Fire is likely. Do not move hot hay yourself — fire-service assistance only.
200°F or higher	Fire is imminent. Do not move hot hay yourself — fire-service assistance only.

NDSU Extension’s specific boundary: once hay is above 175°F, do not move it yourself. Moving overheated or smoldering hay exposes it to fresh oxygen and can cause it to ignite. Call your local fire department and let trained personnel handle it. The same immediate-call, no-move rule applies at any temperature if you see smoke or smell a burning odor — don’t wait for a thermometer reading to confirm what your nose and eyes already suggest. Use a probe thermometer — a sharpened length of pipe with a thermometer lowered on a string works — rather than judging by hand, and never enter or walk on top of a stack you suspect is heating.

Handling, disposal, and buying/selling disclosure

Safe handling

• Store and stack bales on a level, well-drained site so they can’t roll or shift, using chocks or bracing as needed for your stacking method.
• Use a wrapper, loader, or bale-handling attachment rated for the bale’s actual weight — actual weight depends on dimensions, density, moisture, and crop, so confirm it with a representative scale weight or the equipment’s rated capacity rather than assuming based on size alone.
• Keep bystanders, children, and anyone not directly handling equipment clear of the loading and wrapping area.
• Remove all film, net wrap, and twine before turning animals in with a bale or placing it in a feeding ring. The University of Georgia Forage Extension Team specifically advises removing net wrap before placing a bale ring around baled silage. Treat full removal as a standard precaution for any wrap type — leftover film, net, or twine left within reach risks ingestion or entanglement.

Disposal

Used silage film, net wrap, and twine should be contained and disposed of properly — never burned. The Wisconsin Department of Natural Resources notes that burning agricultural plastic is illegal in that state and can release dioxins and other toxic compounds. Rules vary by state and locality — check your own state and local regulations before burning or disposing of agricultural plastic, and look for an agricultural-film recycling program or collection event in your area before defaulting to a landfill.

Buying or selling wrapped dry hay: what to disclose

If wrapped dry hay changes hands, both sides do better with a clear disclosure. A complete one covers:

• Lot or field identifier, crop/species, and cutting or maturity stage
• Whether the crop was rained on after cutting, and the measured moisture percentage (with the method used)
• Storage method and system used — net wrap plus cover, shed, or plastic-wrapped, and which specific method
• Whether a preservative was applied, and which product and rate
• Film or cover product used, if any, and storage duration and conditions since baling
• Any known heating or mold history, and lab test results if available
• Pesticide/herbicide application history and any applicable grazing, haying, or feeding/manure-management restrictions
• Bale dimensions and measured (not estimated) weight
• Price, delivery terms, and an explicit statement that there is no guarantee of suitability for any particular animal or use — the buyer’s veterinarian or nutritionist should confirm fit before feeding

Decision table: what fits your hay

Situation (measured, not guessed)	What it means	Fits this guide
Genuinely dry (below the Purdue unpreserved target for your bale type)	Too little free moisture to ferment; airtight film risks trapping condensation instead	Net wrap + tarp/cover, or a shed. Not film.
Dry hay, no covered storage at all	Narrow case UKY Extension documents, with an expected mold layer	UKY’s specific 2-layer black-film method, verified locally — no feed-safety guarantee
Borderline, ~18–25% (measured)	At or above the Purdue unpreserved target for your specific bale type (20%/18%/17% by package); well below UGA’s ~40% reliable-fermentation boundary	Re-dry, or an effective preservative applied exactly within its label and your package guidance. Not baleage, not casual film sealing.
~40–60%+ (validated baleage moisture, full system in place)	Can ferment and preserve under a correctly managed oxygen-barrier seal	Out of scope here — see dedicated baleage guidance for equipment, layers, and feed-out

Frequently asked questions

Can you wrap dry hay in plastic to store it outside?

It’s not the default recommendation, because airtight film can trap condensation against forage that isn’t wet enough to ferment. The University of Kentucky Forage Extension Program documents a specific exception for producers with no covered storage: roughly 2 layers of black plastic with about 20% overlap, a vertical ventilation cut between bales, and an expectation of a 1–2 inch outer mold layer that’s still less loss than leaving bales fully exposed. Above about 20% moisture, their guidance says mold gets significantly worse.

Why does dry hay mold when it’s sealed in plastic film?

Fermentation needs enough free moisture for lactic-acid bacteria to produce the acid that keeps mold in check. University of Georgia Extension reports that forage under about 40% moisture won’t ferment well, and baling it that dry increases mold and storage losses instead. Sealing hay well below that range in airtight film removes oxygen without adding the acid drop that would normally suppress mold, and extension sources commonly report an outer mold layer as the practical result.

What moisture does hay need to ferment as baleage?

Penn State Extension puts the optimal baleage moisture at about 45–60%, with fermentation possible but increasingly risky from roughly 30% to 70%. University of Georgia Extension adds that forage under about 40% moisture will not ferment well. Truly dry hay, cured well below that range, doesn’t have enough free moisture to ferment when sealed.

I measured my hay at 18–25% moisture — what should I do?

Treat it as a measurement-and-package problem, not a texture call. Purdue Extension’s unpreserved-storage targets are package-specific — 20% for small rectangular bales, 18% for large round, 17% for large rectangular — so where 18–25% sits relative to “dry” depends on your bale type. Either way, the whole range is well below the roughly 40% moisture University of Georgia Extension says forage needs to ferment well, so baleage isn’t a route for hay that tests in this band. Re-confirm the reading with a calibrated tester for your specific package, then either re-dry the hay or apply an effective preservative exactly within that product’s label and your bale type’s package guidance, and store it dry. Baleage only applies to forage an independent check finds in a validated ~40%+ range — a different measurement than this one — and it needs its own complete system, not a casual film seal.

Can I feed hay that has mold on the outside from being wrapped?

No — don’t feed hay with visible mold until a veterinarian or livestock nutritionist has weighed in, regardless of how light the mold looks. Purdue veterinary diagnostician Grant Burcham has traced livestock deaths to improperly preserved forage, and risk varies sharply by species, with horses and pregnant or lactating animals at the highest risk. Visual and smell checks can’t confirm mycotoxin presence, and because mold levels vary within a lot, even a representative lab sample informs a feeding decision rather than certifying the whole lot free of mold or mycotoxin.

Does net wrap make dry hay breathe or dry out faster?

No. Net wrap is an open mesh that binds the bale into shape — that’s its job, not weather management. Its open structure allows more air and moisture exchange than an airtight film, but it is not waterproof and does not actively dry hay that was baled too wet. Keeping weather off a bale is a job for a separate cover, tarp, or shed, plus good site drainage. Hay still needs to be cured to a safe moisture before baling, regardless of what covers it afterward.

The bottom line

Sealing genuinely dry hay in airtight plastic film is not the default move, because it usually trades a weather problem for a mold problem. The University of Kentucky’s documented method is a real, narrow exception for producers with no covered storage — not a general recommendation, and not a feed-safety clearance for the mold it expects to form. Borderline hay in the 18–25% range needs a measured, package-specific decision — re-drying or an effective preservative applied exactly within its label and package guidance — not baleage and not a guess. And once any bale is sealed or stacked, moisture-driven fire risk, safe handling, proper disposal, and honest disclosure if you buy or sell the hay all still apply.

Sources: University of Kentucky Forage Extension Program, “Can I wrap dry hay as an alternative to inside storage?” (forages.mgcafe.uky.edu/baleageq26 — no publication or revision date visible on the source page, accessed August 2026); Penn State Extension, baleage moisture and fermentation guidance (extension.psu.edu/baleage); University of Georgia Cooperative Extension, Bulletin B1508, “Baleage: Frequently Asked Questions” (fieldreport.caes.uga.edu); Purdue Extension Pest&Crop, “Is Your Hay Too Hot?,” citing NRAES-18 (extension.entm.purdue.edu); North Dakota State University Extension, “Preventing Hay Fires” (ndsu.edu); Grant Burcham, DVM, PhD, Purdue University College of Veterinary Medicine, “Reduce the Chances of Listeriosis and Botulism by Using Best Management Practices When Making Silage” (extension.entm.purdue.edu); Mississippi State University Extension, “How Moldy Hay or Baleage Can Impact Livestock Production” (extension.msstate.edu); University of Georgia Forage Extension Team, “Tips for Feeding Baleage” (site.extension.uga.edu/forageteam); Wisconsin Department of Natural Resources, agricultural plastics disposal guidance (dnr.wisconsin.gov). Accessed August 2026.

Featured photo: Round hay bales in covered farmyard storage by Tozina, licensed under CC BY-SA 4.0, via Wikimedia Commons.