Hay is dried forage preserved for later feeding, but its need to maintain a low moisture content makes it highly vulnerable to weather when stored outside. The longevity of hay is determined by how long it retains its nutritional quality and remains safe for consumption, not just how long the bale remains intact. Since hay readily absorbs moisture from the air and ground, outdoor storage immediately initiates degradation. Understanding the timeframe and factors that govern spoilage is important for managing this stored feed.
Average Outdoor Durability
The time hay retains usable quality outside varies significantly based on the level of protection it is afforded. Completely uncovered hay that is left directly on the ground in a typical climate will begin to experience substantial spoilage within one to two months. Research indicates that such unprotected storage can lead to a dry matter loss ranging from 5 to 35 percent, and in high-rainfall environments, losses can even reach 50 percent of the bale’s total weight over a storage period of six to nine months.
When hay is stored with minimal protection, such as being elevated off the ground or having a simple covering, its usable lifespan extends to approximately three to six months. For large round bales, this spoilage is concentrated on the exterior, where the outer four inches of a six-foot diameter bale account for about 25 percent of the total volume. When hay is completely exposed, this outer layer can often be considered unusable after just a few months, resulting in a significant reduction of the feed available to livestock. If the hay is intended for less sensitive uses, like landscaping mulch, it may be considered usable for a longer duration, but its structural integrity will still decline markedly.
Environmental Factors Accelerating Spoilage
The primary mechanism of hay deterioration is the introduction of moisture, which accelerates the activity of microbial organisms. Rain and high humidity provide the necessary water content for mold and bacteria to flourish, leading to fermentation and the breakdown of carbohydrates within the forage. This microbial activity generates heat, which further consumes the hay’s nutrients and contributes to dry matter loss.
Direct contact with the ground is a major source of moisture, known as wicking. Even on dry days, bales resting on soil will draw moisture upward, creating a saturated bottom layer that provides an ideal environment for mold development. Studies have shown that bales stored directly on sod can experience spoilage on the bottom layer affecting 22 to 23 percent of the material in that section. Exposure to sunlight and ultraviolet (UV) radiation also contributes to spoilage, though it is less of a factor than moisture. UV exposure causes bleaching and reduces the concentration of certain nutrients, such as carotene, which is the precursor to Vitamin A.
Techniques for Maximizing Outdoor Storage Life
Preventing Ground Contact
One of the most effective methods for preserving hay outside is to break the direct contact between the bale and the ground to stop moisture wicking. This can be achieved by elevating the bales using wood pallets, old tires, or a layer of coarse gravel that is at least four to six inches deep. Storing hay on a well-drained, slightly sloped site also allows water to run away from the storage area, preventing pooling.
Utilizing Protective Barriers
Covering the hay is important for mitigating the effects of precipitation and can reduce dry matter loss by up to 50 percent compared to uncovered storage. Tarps or specialized bale sleeves offer a protective barrier against rain and snow, but proper tie-downs are necessary to prevent wind damage. Utilizing net wrap instead of traditional twine during baling can also help, as it creates a denser, smoother surface that sheds water more effectively, reducing dry matter losses by as much as 32 percent.
Arrangement and Ventilation
When storing multiple round bales outside, arrangement and ventilation are important considerations for minimizing spoilage. Bales should be placed end-to-end in straight rows with the flat sides touching, minimizing the surface area exposed to the elements. Adjacent rows require a space of at least three feet between them to promote airflow and allow sunlight to penetrate and dry the bales quickly after rainfall. Never stacking round bales in a pyramid pattern outdoors is a widely accepted practice, as this concentrates moisture and hinders the ability of the exposed outer layers to dry effectively.