The term “yellow grass” is ambiguous, referring not to a single plant but to a color that can signal a temporary state, a disease, a harvest product, or an intentional aesthetic choice. Grass is normally green due to the pigment chlorophyll, but it changes to yellow or tan when that pigment is lost or not produced efficiently. Understanding the context—whether the grass is still growing, harvested, or an ornamental variety—determines the correct name for the yellow hue. This discoloration is a symptom of a wide range of conditions, from natural cycles to nutrient disorders and fungal infections.
Dormant Grass and Harvested Products
Grass that is still rooted in the ground but has turned yellow or brown is often described as being dormant. This state is a natural survival mechanism where the plant temporarily stops active growth to conserve energy, typically in response to environmental stresses like drought or extreme cold. The yellow-brown color appears because the plant breaks down its chlorophyll faster than it can produce it, reallocating those nutrients to its root system for protection. This is a temporary condition, and the grass is not dead; the crown and roots remain alive, awaiting favorable conditions like warmer temperatures or rainfall to resume photosynthesis and return to a green color.
The most common name for yellow grass that has been cut and gathered is hay. Hay is a type of forage, which is the general term for plant material eaten by grazing animals, that has been cut, dried, and cured to be stored as animal fodder. The curing process involves reducing the moisture content of the freshly cut grass or legumes, such as alfalfa, to approximately 15-20% to prevent mold and spoilage during storage. This drying process removes the green color and leaves the preserved, nutritious tan or golden product used to feed livestock.
Names for Active Turfgrass Ailments
When grass that should be actively growing turns yellow, the underlying condition is broadly known as chlorosis, which is the general term for the yellowing of plant tissue due to a lack of chlorophyll. Chlorosis is a symptom, not a disease itself, and is often caused by nutrient deficiencies, poor soil conditions, or disease. The specific name given to the yellow grass depends on the precise cause and pattern of the discoloration.
A common cause of uniform yellowing across older grass blades is nitrogen deficiency, as nitrogen is a mobile element the plant recycles from older leaves to support new growth. Conversely, iron chlorosis (iron deficiency) typically manifests as yellowing primarily in the youngest leaves, while the veins may remain a darker green, because iron is an immobile nutrient that cannot be easily moved from older tissue.
Yellowing grass can also be a symptom of several fungal infections, which are often named for the visual pattern they create.
- Dollar Spot, caused by the fungus Sclerotinia homoeocarpa, creates small, sunken, bleached-yellow to straw-colored spots often the size of a silver dollar.
- Rust is named for the yellowish-orange to reddish-brown powdery spores (Puccinia spp.) that cover the grass blades.
- Yellow Patch (Rhizoctonia cerealis) is another fungal disease that creates circular or irregular yellow patches across the turf, especially in cool, wet conditions.
Naturally Golden Ornamental Varieties
In landscaping, “yellow grass” refers to cultivars specifically bred to exhibit a golden or yellowish color throughout the growing season, a color that is natural and desired, not a sign of stress or disease. These varieties often contain a higher concentration of carotenoids or other pigments that mask the green chlorophyll.
‘All Gold’ Japanese Forest Grass (Hakonechloa macra) forms graceful, cascading mounds of bright golden-yellow foliage that thrive in shaded areas. Zebra Grass (Miscanthus sinensis ‘Zebrinus’) is known for its striking horizontal bands of yellow across the green blades. Certain varieties of Feather Reed Grass (Calamagrostis x acutiflora), such as ‘Eldorado’, feature yellow midribs or plumes that ripen to a golden color in the fall.
Clarifying Hay, Straw, and Forage
The large, yellow bales seen in fields are most commonly named hay or straw, which are distinct products. Hay, as previously noted, is the dried grass or legume cut while the plants are still green and nutritious, intended to be a complete feed for livestock.
In contrast, straw is the dried stalk or stem of a grain crop, such as wheat, oats, or barley, that remains after the grain seed head has been harvested. Straw is tan or yellow and is primarily used for animal bedding, mulch, or erosion control because it has very little nutritional value compared to hay. A third product, silage, is yellow or green forage that has been chopped and preserved through fermentation in an anaerobic environment, resulting in a high-moisture fodder.