Hay is a common agricultural product often confused regarding its ability to generate new plant growth. The idea that this dried material can spontaneously sprout is a misunderstanding of how it is processed. Hay is not designed to grow; its creation specifically removes the biological activity necessary for sprouting. Any growth seen when using hay comes not from the dried stalks, but from a separate, often overlooked factor: viable seeds.
Understanding the Difference Between Hay and Grass
Grass is the living plant, typically harvested while green and full of moisture, often up to 80% water content. Hay, in contrast, is the same grass or legume plant (such as alfalfa or clover) that has been cut, dried, and cured for animal feed. The purpose of making hay is preservation, achieved by drastically reducing moisture content to a safe storage level, typically below 20% for small bales.
The curing process involves leaving the cut forage in the field to dry, halting the plant’s biological processes like respiration and photosynthesis. This drying is essential because high moisture encourages microbial growth, which causes spoilage and loss of nutritional value. The final baled product is a preserved, dormant form of the plant material. The dried leaves and stems are no longer biologically active and cannot root or sprout when re-exposed to water.
Why Hay May Still Contain Viable Seeds
The most frequent reason for unexpected growth when hay is used is the presence of viable seeds mixed within the dried stalks. This growth comes from encapsulated seeds that survived the harvesting and drying process, not the hay itself. The timing of the harvest significantly determines seed presence, as grass cut after it has gone to seed will inevitably contain mature seed heads.
For a seed to remain viable, it must be dried to a low moisture content, typically between 5% and 12%, a condition often met within the cured hay bale. The hay-making process does not involve high-heat sterilization, allowing mature seeds that are dry or protected within the plant structure to easily survive. These seeds, whether from the forage crop or from weeds, lie dormant until they encounter the moisture and warmth needed for germination. When hay is spread as mulch or bedding and watered, these viable seeds activate and sprout, creating the perception that the hay is growing.
Choosing Hay or Straw for Practical Use
When choosing a dried plant material for practical applications like mulching, the potential for unintended growth is a key factor. Hay is composed of whole, leafy grasses and legumes. Due to its purpose as animal feed, it is often harvested at a stage containing a high number of seeds. This high seed content makes hay a less desirable choice for mulching, as it can introduce unwanted grass or weed seeds into a garden bed.
Straw, by contrast, is the dry stalk left over after cereal grains like wheat, oats, or barley have been harvested. The grain heads, which contain the seeds, are typically removed during harvesting, leaving behind hollow, primarily seedless stems. This structural difference makes straw a superior option for gardeners who wish to suppress weeds and retain soil moisture without introducing new plant growth. While some grain seeds may still be present, the probability of widespread sprouting is significantly lower than with hay, making straw the preferred material.