Zoysia grass is a favored choice for many lawns due to its dense growth and ability to thrive in various climates. When properly maintained, it presents a lush, green appearance. However, Zoysia lawns can develop a yellow hue, indicating an underlying issue. Understanding the common reasons for yellowing and implementing targeted solutions can help resolve this problem.
Identifying the Causes of Yellow Zoysia
Yellowing in Zoysia grass can stem from several factors, each leaving distinct visual cues. Nutrient deficiencies, particularly in nitrogen and iron, often cause a generalized yellowing or interveinal chlorosis, where leaf veins remain green while the tissue between them turns yellow. Nitrogen deficiency typically results in a pale green to yellow appearance and stunted growth.
Watering practices significantly impact Zoysia grass health. Both overwatering and underwatering lead to discoloration. Overwatering can saturate soil, depriving roots of oxygen and causing root rot, which manifests as pale yellowing or browning. Conversely, underwatering or drought stress causes grass blades to become dry, brittle, and yellow as the grass attempts to conserve moisture or enters dormancy.
Pests and diseases also contribute to Zoysia grass yellowing, often in specific patterns. Chinch bugs, small insects that feed on grass sap, create irregular patches of yellow or brown turf, frequently appearing in hot, sunny areas. Grubs, the larvae of various beetles, feed on grass roots, leading to patches of yellow or brown grass that can be easily pulled up. Fungal diseases like rust produce orange-to-red powdery spots on grass blades. Other fungal issues, such as brown patch or dollar spot, cause circular patterns of yellow or brown discoloration.
Environmental stressors, including temperature extremes, can influence Zoysia’s color. Excessive heat can cause stress, leading to yellowing or browning. Cold temperatures trigger natural dormancy, where the grass turns tan or brown until warmer conditions return. Chemical exposure, such as herbicide drift or over-application of fertilizers, can also result in yellowing or “burning” of the grass. Soil compaction restricts root growth and nutrient uptake, contributing to yellowing due to poor drainage and reduced oxygen availability.
Mowing practices and underlying soil problems can also lead to yellow Zoysia. A dull mower blade tears grass blades, leaving frayed tips that turn yellow or brown. Mowing the grass too short, known as scalping, stresses the plant and can expose sensitive lower parts of the blades to excessive sun, causing yellowing. Soil pH imbalances affect nutrient availability, potentially leading to deficiencies and yellowing.
Solutions for Reviving Yellow Zoysia
Addressing nutrient imbalances begins with a soil test to identify specific deficiencies. For general yellowing, a nitrogen-rich fertilizer (e.g., 16-4-8 or 15-0-15 NPK ratio) applied at recommended rates, typically 2 to 4 pounds of nitrogen per 1,000 square feet annually, can promote greening. If iron deficiency is diagnosed, an iron supplement can quickly enhance the grass’s green color. Slow-release granular fertilizers provide a steady nutrient supply and prevent rapid growth that leads to thatch buildup.
Optimizing watering practices is important for Zoysia’s health. Zoysia grass generally requires about 1 to 1.5 inches of water per week, including rainfall, during its active growing season. Deep, infrequent watering encourages deeper root growth, making the grass more drought-tolerant. Watering early in the morning allows grass blades to dry before nightfall, reducing the risk of fungal diseases. Checking soil moisture ensures water is applied only when needed.
Managing pests and diseases involves identifying the specific problem to apply targeted treatments. For chinch bugs, insecticidal soaps or insecticides can be effective. Grubs can be controlled with beneficial nematodes or insecticides applied when larvae are young, typically in late spring or early summer. Fungal diseases like rust, brown patch, or dollar spot may require fungicides, alongside cultural practices such as improving air circulation and proper watering to reduce humidity. Removing diseased grass clippings can also prevent the spread of fungal spores.
Mitigating environmental stress involves protective measures and proper care. During extreme heat, adjusting watering schedules to provide up to 2 inches per week can help the grass cope. Zoysia’s natural dormancy in colder temperatures means yellowing in winter is expected and does not require intervention. When applying chemicals, carefully follow product labels to avoid over-application or drift, which can burn the grass. If soil compaction is an issue, core aeration can help by removing small plugs of soil, improving air, water, and nutrient penetration to the roots.
Improving mowing and soil health contributes to preventing yellowing. Zoysia grass should be mowed to a height of 1 to 2 inches, with no more than one-third of the blade removed in a single mowing session. Sharpening mower blades regularly ensures a clean cut, preventing frayed tips that turn yellow. For soil pH imbalances, a soil test will indicate whether lime is needed to raise pH or sulfur to lower it. Annual core aeration helps alleviate compaction and break down thatch, promoting soil health and root development.
Preventing Future Yellowing
Proactive measures are important for maintaining the vibrant green color of Zoysia grass and preventing future yellowing. Regular soil testing, ideally every few years, provides information about nutrient levels and pH, allowing for timely adjustments before deficiencies impact grass health. Establishing a consistent fertilization schedule based on soil test results ensures the grass receives necessary nutrients throughout its active growing season.
Proper watering habits are important. Deep, infrequent watering encourages a robust root system, making the lawn more resilient to dry periods and less susceptible to disease. Routine monitoring for pests and diseases allows for early detection and intervention, preventing small issues from escalating. Adhering to proper mowing techniques, including maintaining the correct height and using sharp blades, reduces stress on the grass. Annual core aeration also helps prevent soil compaction and thatch buildup, ensuring roots have access to air, water, and nutrients.
When to Consult a Professional
There are instances when Zoysia grass continues to exhibit persistent yellowing or other concerning symptoms despite diligent efforts. If DIY solutions do not yield noticeable improvement, or if the yellowing is widespread and spreading rapidly, professional help may be warranted. Rapidly expanding patches of discolored grass, especially if accompanied by signs of severe pest infestations or unusual disease patterns, can indicate a problem beyond typical homeowner remedies. A lawn care specialist, arborist, or local extension office can conduct a thorough diagnosis, including advanced soil analysis, to pinpoint complex issues. They can then recommend tailored treatment plans that might involve specialized products or techniques not readily available to the average homeowner.