What covering hay is worth, from published research
Dry matter loss by storage method
| Storage method | 0 to 9 months | 12 to 18 months |
|---|---|---|
| On the ground, covered | 5 to 10% | 10 to 15% |
| On the ground, exposed | 5 to 20% | 20 to 35% and more |
| Elevated on pallets or tires, covered | 2 to 4% | 5 to 10% |
| Elevated, exposed | 3 to 15% | 12 to 35% |
| Under an open building | 2 to 5% | 3 to 10% |
| Enclosed barn | over 2% | 2 to 5% |
Large round bales. Source: N1 · Mississippi State University Extension, publication P2540 (POD-04-23), table 2
Two things in that table are worth more than the headline. First, the cover and the base work together: elevated but left exposed, bales still lose up to 35 percent over the long window, against 15 percent at most covered on the ground, and 10 percent at most elevated and covered. A cover on a bad base is doing half a job. Second, the gap widens with time. Over nine months, covered and exposed on the ground overlap; over eighteen months they do not come close.
The cost of not doing it
Storing on the ground rather than in a barn costs 1,200 to 1,600 USD a year more for a 30 head herd over 180 days in harvested hay, or 3,120 to 4,095 USD in purchased hay.
Source: N1 · Mississippi State University Extension, publication P2540 (POD-04-23)
Set that against what covers actually cost. Published US retail for the sizes that two vendors both carry runs from about three hundred dollars to about seven hundred and sixty, depending on size and vendor, and not reliably on thickness. Every figure, with its source and the date it was read, is on the specs and prices comparison.
The warning that costs people a stack
The instinct is reasonable and the result is not: a sheet under the bales turns the base into a tray. The published recommendation is a well drained base instead, and growers describe building one from coarse rock. It is also the cheapest line in this whole decision.
When published guidance says not to cover at all
- Cover after the sweat, not at baling. Stacking and covering straight after baling risks heating and moulding; growers and published guidance advise letting bales sit one to two weeks first. (N3 · published grower and extension guidance, read 2026-08-20)
- Bale temperature peaks 7 to 10 days after baling. Bales over 20 percent moisture carry a heating risk and may need monitoring for up to 30 days. (N3 · published grower and extension guidance, read 2026-08-20)
We are quoting this, not promising it. How forage keeps depends on the hay, the moisture at baling and the site, none of which a fabric specification controls. A cover is storage protection, not a repair for hay that went up wet, and any supplier who tells you otherwise is selling you something they cannot deliver. It is also why our written quotes cover the cover, and never the forage under it.
How much hay this concerns
- 49.56 million acres of hay harvested in 2025, against 49.39 million in 2024. (N1 · USDA NASS, Crop Production Annual Summary 2025, reported 2026)
- 123.03 million tons of all dry hay in 2025, up 0.5 percent on 2024. (N1 · USDA NASS, Crop Production Annual Summary 2025)
- Texas 5.10 million dry hay acres, Oklahoma 3.34 million. (N1 · USDA NASS, Crop Production Annual Summary 2025)
- How much of it is stored outside under a cover: No statistic isolates how much of that acreage is stored outside under a cover. Stated as missing, never estimated.
Questions
How much hay do you lose storing round bales on the ground?
Mississippi State Extension publishes 5 to 20 percent dry matter loss over 0 to 9 months exposed on the ground, and 20 to 35 percent or more over 12 to 18 months. Covered on the ground, the same table gives 5 to 10 percent and 10 to 15 percent. Elevated on pallets or tires but left exposed, it gives 3 to 15 percent and 12 to 35 percent, a higher top end than covering on the ground; elevated and covered, 2 to 4 percent and 5 to 10 percent.
Is a hay tarp worth the money?
That depends on the value of what is under it, which is your figure and not ours. What is published is the loss gap by storage method and the cost gap between ground and barn storage: 1,200 to 1,600 USD a year for a 30 head herd over 180 days in harvested hay. A cover is the cheap end of closing part of that gap; a barn is the expensive end.
Should I put plastic under the bales as well as over them?
The published extension guidance says no: water could pool inside the cover. The same guidance recommends a well drained base instead, and growers describe building one out of coarse rock. In the loss table, bales elevated on pallets or tires and covered lose the least of any outdoor storage: 2 to 4 percent, then 5 to 10 percent.
When can a stack be covered after baling?
Published guidance is to let the hay finish sweating first, generally one to two weeks, because bale temperature peaks about seven to ten days after baling and covering too early risks heating and mould. Bales above 20 percent moisture carry a heating risk. That is published guidance we cite, not a promise we make: it depends on your hay and your site.
Next: where hay tarps actually fail, and the family page, hay tarps specified where they actually fail.
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