Storing Net-Wrapped Round Bales Outside: Loss, Stacking & Drainage

By the XES Netting team — bale net-wrap manufacturer · Updated August 16, 2026 · ~12 min read

What outdoor storage actually costs you

Published dry-matter loss figures for outdoor round bale storage vary widely, because they depend on climate, storage length, bale density, and what the bale is sitting on. Note the geography attached to each row — the highest figures come from the humid Southeast and do not transfer to a dry Western climate. But the direction is never in doubt, and the spread is worth seeing honestly rather than as a single tidy number:

Two things are worth pulling out of that table. First, the figures behind a 25–40% headline come from Southeast conditions (Mississippi State and Univ. of Tennessee), not from every climate — wetter, warmer regions weather bales faster, and the published span across studies runs from about 2% to over 50% depending on climate, storage length and what the bale sits on. Where those Southeast numbers do apply, they mean losing roughly one bale in three or four. Second, look at the gap between "gravel, uncovered" at 30–40% and "rack plus cover" at about 6%: elevation alone is not the whole answer. It helps a great deal, but in Tennessee's numbers it is elevation and cover together that get outdoor storage close to barn performance.

To put that in dollars, SDSU Extension works a useful example: a 4-inch weathered layer on a 6-foot bale is about 21% of the bale's volume. Multiply that by your own hay value — our guide to pricing hay will help you put a real number on a bale — and the cost of a storage pad usually stops looking expensive.

Where the loss happens

Extension sources consistently identify ground contact as the primary loss zone. When a bale sits on soil or sod, moisture wicks up into the bottom of the bale and that zone stays wet long after the surface has dried. Mississippi State puts it simply: most storage losses occur where hay bales touch soil.

The top surface matters too — UNL describes the two moisture pathways as rain and snowmelt soaking in from above while the bottom wicks from the ground — but the bottom is where a bale rots rather than merely weathers. Mississippi State notes that over a long storage period up to 8 inches of the outer layer can be lost to weathering, and NC State's rule of thumb is that average surface loss runs about 4 inches, or roughly 20% of the bale — one bale in five.

The practical consequence: a wrap, however good, binds and sheds. It does not break the capillary path between wet soil and hay. That is a job for what you put under the bale, which is why base preparation earns its own detailed guide.

Getting bales off the ground

This is the highest-return change most operations can make. Extension recommendations converge on a few options:

• Coarse rock base. UNL recommends a well-drained location with a 4–6 inch coarse rock base to minimize bottom spoilage. This is the most specific and most commonly recommended surface.
• Pallets. Mississippi State lists pallets alongside gravel as a way to minimize dry-matter loss. Often free from distribution centers; expect to replace them as they rot.
• Old tires. Recommended by both Mississippi State and NC State — but Mississippi State adds the caveat that tires may hold water, which matters in mosquito country and in freeze–thaw climates.
• Cross ties or poles. NC State includes cross ties in its list of surfaces that limit wicking from ground moisture.

Kentucky Extension puts a number on the payoff: breaking ground contact can reduce dry-matter loss by up to 38%. That is a relative improvement, not an absolute one — it takes a 30% loss toward the high teens, it does not take it to zero.

A note on highway guardrail, which comes up constantly in producer discussions as a cheap elevated base: it is a real and widely used practice, and the physics is the same as poles or cross ties. But it does not appear in the Extension publications reviewed for this guide, so treat it as accumulated producer practice rather than a researched recommendation.

Row orientation and spacing

Mississippi State's guidance is the clearest: place bale rows in a north–south orientation so the sun shines evenly over the bales from east to west, butt the flat ends of round bales together firmly to provide a barrier to precipitation, and allow at least 3 feet between rows for air circulation. NC State agrees on north–south and suggests 18 inches between individual bales or 3 feet between rows. UNL frames it slightly differently — rows running northwest to southeast where possible, with adjacent lines at least 10 feet apart.

So the direction is settled and the spacing is not. Three feet and ten feet are both defensible; wider rows dry faster and cost more ground. The reason the direction matters is straightforward: an east–west row leaves one long side of every bale permanently shaded, and that side stays damp.

One genuine open question: whether to butt bale ends tightly or leave a gap. Mississippi State says butt them firmly, to keep rain and snow off the flat faces. Field-day work reported through Ohio State notes that a 12–18 inch gap allows better airflow — and states plainly that there is no research consensus on the ideal distance between bales. In a wet climate the sealed-face argument is stronger; in a humid one with less driving rain, airflow may win.

Stacking outdoors: what one field demonstration measured

Stacking is widely discouraged outdoors, and the most concrete US data point comes from a single on-farm field demonstration rather than a multi-site trial. Moisture mapping presented at an SDSU field day and reported through Ohio State Extension compared storage methods on one South Dakota farm in 2019, taking approximately 50 probe samples at eight-inch depth from the flat face of each bale, after a season that delivered more than 20 inches of rain. Treat it as one well-documented demonstration, not a universal result:

• Bales under an open shed: about 98% of the sampled area was at or below 20% moisture.
• Bales in tightly packed outdoor rows: more than two-thirds of the sampled area exceeded 22% moisture.
• Middle and bottom tiers of a pyramid stack: more than 35% of the sampled area exceeded 30% moisture.
• Bottom bale of a "mushroom" stack (one bale flat-end down, a second laid round-side down on top): more than 45% of the sampled area was over 35% moisture — the worst result measured.

The proposed mechanism is straightforward: water sheds off the upper bales onto the lower layer, where limited airflow and sun keep it wet, and the bottom bales squat under the load and make more contact with the ground. The recommendation from that work is blunt — avoid stacking outdoors, and if limited space forces it, cover the pile.

Mississippi State allows one narrow exception worth knowing: pyramid stacking with a tarp, for storage periods shorter than about 90 days. Stacking is a different calculation indoors, where the roof has already removed the water.

Does covering pay?

UNL's summary of the research is that outdoor storage losses run 5–35%, that indoor storage cuts those losses by about two-thirds, and that good plastic covering outdoors cuts them by about half. Mississippi State is more conservative, reporting that these low-cost approaches reduced storage loss by about 15% in some studies.

Rather than quoting a break-even hay price, do the arithmetic with your own numbers, because it turns entirely on bale value and tarp life:

• What you save = (loss without cover − loss with cover) × number of bales × value per bale.
• What it costs = tarp price ÷ years of tarp life ÷ bales covered, plus the labour to put it on and take it off.

Work an example on a 100-bale stack: if covering takes loss from 25% to 12% on hay worth $70 a bale, that is 13% × 100 × $70 = $910 saved in a season. Against that, put the real cost of the tarp, its expected life, and — the number people forget — the hours of labour. Where that labour is the binding constraint, elevation and orientation are the moves that cost nothing recurring. If you do decide to cover, our bale tarp selection guide compares the options.

What net wrap does — and doesn't do — outdoors

What it does. Net wrap measurably outperforms twine in outdoor storage. The most-cited comparison is a single six-month University of Wisconsin trial on large round alfalfa bales (Shinners et al., 2002), reported by SDSU Extension: net-wrapped bales lost about 7.3% of dry matter versus about 11.3% for twine-tied. One trial, one crop, one climate — directionally consistent with the rest of the literature, but not a guaranteed margin on your farm. UNL's explanation of why matches what producers see — net wrap reduces bale sag, holds bale shape, and creates a tight, smooth surface that sheds water and resists weathering, insects and rodents. The SDSU work reaches the same conclusion: use net wrap instead of twine so bales shed water and hold their shape. Our net wrap vs twine comparison covers the cost side of that trade.

What it does not do. About four percentage points in one six-month Wisconsin trial of large round alfalfa bales is a real gain, but notice what it is not: it is not the difference between 30% and 5%. Wrap improves the top and sides of the bale. It does nothing about the bottom, because nothing you put around a bale changes what is underneath it. This is why an operation can buy the best wrap available and still lose a quarter of its hay — the wrap was never the limiting factor. Elevation, orientation and drainage are.

On UV life. Manufacturers publish UV-stability specifications for net wrap, and those specifications are worth reading before you buy — see UV protection in bale net wrap and whether net wrap goes bad in storage. Be aware that these are manufacturer specifications, not Extension field trials; no land-grant study reviewed here publishes month-by-month strength data for net wrap under field exposure. Treat published UV ratings as a comparison tool between products rather than a guarantee of a specific service life.

Leave the wrap on until you feed

Do not remove net wrap from a bale that is still sitting in outdoor storage. This is worth stating plainly because it is a mistake with a certain logic to it — the wrap is the thing that will eventually need disposing of, so why not take it off early on a dry day?

Because the wrap is the only thing holding the bale in its shape. Strip it off a bale that stays outside and you get all of the following: the bale slumps and loses density, the entire surface is exposed to rain and snow instead of a shedding skin, moisture drives into the open outer layer, spoilage accelerates, and the bale becomes difficult or impossible to move without falling apart.

Every Extension source reviewed treats net wrap as a storage-duration protection and recommends removing binding only immediately before feeding or processing. The rule is simple: wrap comes off at the feeder, the bale processor, or the mixer — not in the stackyard.

Then take every piece of it off

Plastic net wrap and plastic twine are not digested. University of Nebraska–Lincoln reports that plastic net wrap and biodegradable-plastic twine are not digested and can accumulate in the rumen over time, while sisal twine digests only slowly — so all binding should still be removed — and that grinding or processing does not remove the risk — it chops the plastic into pieces that still collect in the rumen. Removing wrap "mostly" is not the same as removing it. Pull the whole sheet, check the bale face for strands that tore free, and contain what you remove so it does not end up in a feed alley or a field.

Removing and moving bales safely

Large round bales are heavy enough to kill, and most of the risk sits in the handling rather than the wrap. Penn State Extension and Virginia Tech both cover this in detail. The working rules:

• Use equipment rated for the bale weight, with an attachment matched to the loader and the bale — not an improvised spike.
• Carry the load low. A raised bale moves the centre of gravity up and forward and is the classic tip-over setup, especially on slopes.
• Work on firm, level ground. Soft or sloping ground under a loaded machine is how stacks and tractors go over.
• Before you get off or start cutting wrap: park, set the brake, lower the load to the ground, shut the engine down and take the key.
• Stand outside the crush path — never downhill of a bale that could roll, never between a bale and a fixed object.
• Never work under a suspended bale, and never let anyone else stand under one either.
• Remove and contain every piece of wrap or twine before the bale reaches a feeder, grinder, processor or mixer.

If cold weather is what makes removal awkward, the answer is technique rather than taking the wrap off early while the bale is still in storage.

Before you feed it: moisture and spoilage triage

Storage decisions and feeding decisions are linked, because a bale that went up wet is both a fire risk and a feed risk. NDSU Extension targets 18% moisture or less for untreated large round bales. Practical triage:

• Inventory as you stack — record cutting, date baled and condition, so you know which bales to watch and which to feed first.
• Segregate anything questionable and monitor it for about six weeks rather than burying it in the middle of a stack.
• Feed the sound but weather-exposed bales first, and keep the best-protected hay for when you need it.
• Isolate mouldy, musty or heat-damaged bales and get them assessed before you make a feeding decision. Ohio State Extension covers the effects of mouldy feed on cattle; testing beats guessing, and your veterinarian or nutritionist should make the call for pregnant or young stock.

And do take the wrap fully off before feeding — see reducing round bale feeding waste.

Heat and hay fire: the first six weeks

Newly baled hay heats. That is normal, and Alabama Extension notes properly cured hay can reach about 120°F in the first few days after baling — it only becomes a fire hazard when those temperatures fail to come back down after the first sweat. Mississippi State puts the initial stage at 130 to 140°F, with normal sweating at 15–20% moisture continuing for up to ten days.

Above that, the numbers get serious quickly. Purdue Extension publishes the clearest action table:

Alabama Extension adds a sobering note: once a bale reaches roughly 150°F the temperature will not come back down on its own, and spontaneous combustion becomes imminent. Purdue also warns that spontaneous combustion can develop three to four weeks after baling — so a bale that felt fine on day two is not proof of anything. Monitor through the first six weeks, not the first 48 hours.

Common mistakes checklist

• Storing on weedy or muddy ground. Weeds hold moisture against the bale and mud breeds mould. Clean, bare, well-drained ground is better; a rock pad is better still.
• Putting bales in a low spot. Even a shallow depression collects runoff and keeps bales damp all spring. Site selection is free.
• Stacking outdoors to save room. The moisture readings above point the same way, and the mushroom pattern measured worst of those sampled.
• Packing rows tight against each other. Butting the flat ends together is recommended; crowding the rows is not. Leave the row spacing your climate justifies.
• Assuming hay is safe after two days. Heating can build for three to four weeks. Probe, and keep probing.
• Removing net wrap while bales are still stored outside. The wrap is structural. It comes off at feeding.
• Buying premium wrap and skipping the pad. Wrap buys you a few percentage points. The base and the site are worth far more.

Frequently asked questions

How much hay do net-wrapped bales lose stored outside?

It depends far more on what the bale is sitting on than on the wrap. In the humid Southeast sources cited here, Mississippi State puts outdoor storage on the ground at 25 to 30 percent dry-matter loss and University of Tennessee at up to 40 percent; across climates and studies NC State cites a 2 to 52 percent range and UNL cites 5 to 35 percent. Barn storage runs 2 to 6 percent. Net wrap itself was worth about four percentage points against twine in one six-month Wisconsin trial of large round alfalfa bales, not the difference between those extremes.

Is net wrap better than twine for storing bales outside?

Yes. One six-month Wisconsin trial of large round alfalfa bales measured about 7.3 percent dry-matter loss net-wrapped against about 11.3 percent twine-tied — about four percentage points in that single trial. UNL explains why: net wrap reduces bale sag, holds bale shape, and gives a tight smooth surface that sheds water and resists weathering, insects and rodents. Extension sources consistently recommend net wrap over twine for outdoor storage.

Should I take the net wrap off bales stored outside?

No. Remove net wrap only immediately before feeding or processing. The wrap is what holds the bale's shape and sheds water; stripping it from a bale that stays outdoors makes it slump, exposes the whole surface to rain and snow, accelerates spoilage, and can leave the bale too fragile to move. If frozen wrap is the problem, use a removal technique suited to cold weather rather than taking it off early.

What is the cheapest way to cut outdoor bale storage loss?

Break ground contact and pick a better site. Kentucky Extension reports that breaking ground contact can reduce dry-matter loss by up to 38 percent, and UNL recommends a well-drained location with a 4 to 6 inch coarse rock base. Pallets, old tires and cross ties are also recommended by Extension, though tires can hold water. Then run rows north-south with the flat ends butted together, and do not stack.

Which way should I orient rows of round bales outside?

North-south, so the sun crosses the bales evenly from east to west, with the flat ends butted firmly together to shed precipitation. Mississippi State and NC State both recommend at least 3 feet between rows; UNL suggests rows running northwest to southeast with at least 10 feet between lines. An east-west row leaves one long side of every bale permanently shaded and damp.

Can I stack round bales outside if I am short on space?

It is widely discouraged. Moisture mapping at a single 2019 South Dakota field demonstration, using approximately 50 probe samples at eight-inch depth from the flat face of each bale, found more than 35 percent of the sampled area of pyramid-stack middle and bottom tiers above 30 percent moisture, and more than 45 percent of the bottom bale of a mushroom stack above 35 percent moisture, versus about 98 percent of shed-stored bales at or below 20 percent. If space forces stacking, cover the pile; Mississippi State treats tarped pyramid stacking as acceptable only for periods under about 90 days.

How hot is too hot for a freshly baled round bale?

Some heating is normal — properly cured hay can reach about 120°F in the first few days, and 130 to 140°F during the initial sweat. Purdue Extension's thresholds: 125°F or below needs no action; at 150°F check twice daily and separate stacked hay only if it is possible to do so safely; at 160°F check every few hours and again separate the stack only if it is safe to do so; at 175°F stop air movement and alert the fire service; at 190°F fire is likely, so remove hay only with fire-service assistance; and at 200°F or above fire is imminent and hay should be removed only with fire-service assistance. Keep monitoring through the first six weeks, since combustion can develop three to four weeks after baling.

The takeaway

Outdoor storage is the reality for most producers, and it does not have to mean losing a quarter of the crop — but the honest starting point is that bales on bare dirt lose 25 to 40 percent in the humid Southeast sources cited here, with a far wider span across climates — not five. Net wrap is genuinely the better binding and was worth about four percentage points against twine in one six-month Wisconsin trial of large round alfalfa bales, which is worth having and worth paying for. It is simply not the lever that closes the gap. Elevation on a drained base, north-south rows with butted ends, a site that does not pond, no stacking, and a cover if the labour is there — those are the moves that take outdoor storage from disastrous toward barn-like. Then leave the wrap alone until the bale reaches the feeder.

Where net wrap does earn its keep is holding a dense, well-shaped bale together through a full season of weather. A tight, full-width XES® bale net wrap is built for that exposure — compare specifications in our best bale net wrap guide, and see the full round bale storage guide for indoor and mixed setups, or Midwest winter storage for snow-country specifics.

Sources: Mississippi State University Extension, "Hay Storage: Dry Matter Losses and Quality Changes" (extension.msstate.edu, accessed August 16, 2026); University of Nebraska–Lincoln Extension BeefWatch, "Minimizing Storage Losses of Round Bale Hay," 2022 (beef.unl.edu, accessed August 16, 2026); University of Tennessee Extension, "Forage Management: Each Bale Counts" (utbeef.tennessee.edu, accessed August 16, 2026); NC State Cooperative Extension, "Round Bale Hay Storage" (burke.ces.ncsu.edu, accessed August 16, 2026); South Dakota State University Extension, "Best Management Practices for Reducing Dry Hay Storage Loss" (extension.sdstate.edu, accessed August 16, 2026); Ohio State University Extension, "What's Wrong With Stacking Round Bales?" reporting SDSU field-day moisture data (u.osu.edu, accessed August 16, 2026); Purdue University Extension, "Is Your Hay Too Hot?" (extension.entm.purdue.edu, accessed August 16, 2026); Alabama Cooperative Extension System, "Reducing the Risk of Hay Fire" (aces.edu, accessed August 16, 2026); University of Wisconsin Extension A3677, "Big Bale Forage Storage" (forages.org mirror, accessed August 16, 2026); Shinners et al., University of Wisconsin, 2002, six-month large-round-alfalfa net wrap vs twine outdoor storage trial, as reported by South Dakota State University Extension, "How Will You Make Hay This Year?" (extension.sdstate.edu, accessed August 16, 2026); University of Nebraska–Lincoln Extension BeefWatch, "Hold the Net Wrap and Twine," 2024 (beef.unl.edu, accessed August 16, 2026); Penn State Extension, "Safely Moving and Storing Large Hay Bales" (extension.psu.edu, accessed August 16, 2026); Virginia Tech, large round bale handling safety (vtechworks.lib.vt.edu, accessed August 16, 2026); North Dakota State University Extension, "Preventing Hay Fires Due to Excessive Moisture" (ndsu.edu, accessed August 16, 2026); Ohio State University Extension, "Moldy Feed and the Potential Effects on Cattle" (u.osu.edu, accessed August 16, 2026). Dry-matter loss figures vary widely with climate, storage duration and bale density; treat published ranges as indicative and measure your own losses where you can.