Yellow grass, known as chlorosis, signals that your lawn is under stress. This discoloration is a symptom, not a disease, indicating insufficient chlorophyll production. Chlorophyll is the green pigment that captures sunlight for photosynthesis, the process by which grass produces energy. When chlorophyll levels drop, the grass loses its vibrant green color and reveals underlying yellow pigments. Diagnosing the cause requires observing the specific patterns of discoloration, soil conditions, and the lawn’s environment.
Nutrient Deficiencies
Yellowing grass often indicates a lack of essential nutrients needed for chlorophyll production. The most common deficiency is nitrogen, a mobile nutrient. When nitrogen is scarce, the plant relocates it from older tissue to support new growth, causing a uniform, pale yellowing across the oldest blades first. This widespread appearance suggests the entire lawn is undernourished.
Deficiencies in iron or magnesium are also common. Unlike nitrogen, these nutrients are immobile. This results in interveinal chlorosis, where the veins of the younger, newest blades remain green while the tissue between them turns yellow. Iron deficiency is common in high pH soils, which bind the iron and make it unavailable to the roots.
If the yellowing is uniform and starts in old growth, a nitrogen-rich fertilizer usually corrects the problem quickly. If new growth is yellow with green veins, the lawn requires chelated iron or a magnesium supplement, formulated for absorption in alkaline soil conditions.
Improper Watering Techniques
Both too much and too little water can cause yellowing grass. Underwatering, or drought stress, causes blades to curl inward to conserve moisture. The lawn develops a dull, blue-gray tint before turning yellow, and footprints remain visible. The soil in these areas feels dry and hard.
Conversely, overwatering and poor drainage suffocate the grass roots by displacing oxygen. This lack of oxygen causes root function to decline, leading to root rot and an inability to absorb nutrients. Overwatered soil feels squishy and soggy, favoring fungal growth. To avoid both extremes, use deep, infrequent watering to encourage strong, deep root systems.
Identifying Fungal Diseases and Pests
Fungal diseases and insect pests create localized, patterned damage that manifests as yellowing. Fungal diseases thrive in high humidity and excessive leaf wetness.
Fungal Diseases
- Rust disease appears as small yellow or orange spots that rupture, leaving a powdery, rust-colored residue.
- Dollar Spot creates small, straw-colored spots, often with a darker, reddish-brown ring around the patch perimeter.
Insect Pests
Pests targeting the root system often cause yellowing patches mistaken for drought stress.
- Grubs, the larvae of beetles, feed on grass roots, causing irregularly shaped patches that can be easily lifted or rolled back like a carpet.
- Chinch bugs feed on grass blades and inject a toxin that blocks water and nutrient movement, resulting in large, dry, yellow patches that quickly turn brown.
Mowing, Soil Compaction, and Chemical Stress
Maintenance and soil structure factors can induce yellowing in the lawn.
Maintenance Issues
Cutting too much of the grass blade at once, known as scalping, shocks the plant and removes photosynthetic material. This stress exposes the pale, yellow-brown lower stems, causing temporary yellowing until the grass recovers. Never remove more than one-third of the blade height during a single mowing session.
Soil Compaction
Compaction occurs when soil particles are pressed together, reducing space for air and water. This prevents oxygen from reaching the roots and restricts their ability to absorb water and nutrients, leading to decline and chlorosis. Symptoms include water pooling on the surface and thin, sparse grass growth.
Chemical Stress
Misapplication of lawn care products causes chemical stress. Fertilizer burn, from applying too much nitrogen, draws water out of the roots, causing rapid desiccation and yellowing. Herbicide drift, the accidental application of weed killer, causes irregular patches of yellowing or bleached turf.
Next Steps: When to Call a Professional
Homeowners can correct common yellowing issues, such as nutrient deficiencies or improper watering, with minor maintenance adjustments. If the problem is widespread, persistent, or does not respond to basic corrections, seek expert help.
A professional should be consulted for severe pest infestations or persistent fungal disease outbreaks that require targeted pesticide or fungicide application. Complex structural issues, such as soil pH imbalances or severe compaction, also warrant professional intervention. Professionals perform comprehensive soil tests to identify nutritional deficits or pH levels, providing the data necessary to select correct amendments, such as specialized iron treatment or full lawn aeration.