Browning ornamental grass is a common symptom with various causes, ranging from natural, expected cycles to environmental stress or the presence of pests and diseases. To address the discoloration effectively, accurately diagnose the underlying issue. Evaluating the pattern of browning and the time of year it occurs helps narrow down the potential culprits and determine the appropriate action.
Is the Browning Expected? (Natural Cycles and Dormancy)
Browning is often part of a natural process called senescence, which is the aging and die-back of foliage. This mechanism allows the plant to recycle nutrients, particularly nitrogen, from the aging leaves back into the crown and roots for storage. The degradation of chlorophyll, the green pigment, reveals the underlying straw or tan colors of the leaf tissue.
Warm-season grasses, like switchgrass or fountain grass, naturally turn brown in late fall or early winter, signaling the onset of dormancy. This temporary state conserves energy in the root system and crown to prepare for spring growth.
Cool-season grasses, such as feather reed grass, may also brown out during intense mid-summer heat and drought, recovering once cooler temperatures and moisture return. Browning during predictable periods of climatic stress is typically not a cause for alarm, but a signal that the plant is preparing for rest.
Environmental and Cultural Stress (Water, Soil, and Placement Issues)
When browning happens outside of the expected dormancy period, it frequently points to issues with water management, soil conditions, or improper site placement. The most common cultural issue is water stress, which can result from either too little or too much moisture.
Underwatering, or drought stress, causes the grass blades to wilt, curl, and then turn brown as the plant attempts to conserve its remaining moisture. Conversely, overwatering or poor soil drainage can also lead to browning, often starting as yellowing before progressing to brown.
Excess water saturates the soil, displacing the oxygen needed by the roots, which can lead to root rot. Roots damaged by rot cannot efficiently absorb nutrients or water, causing the foliage to die back. Checking the soil moisture several inches down helps determine if the problem is a thirsty plant or a drowning one.
Chemical imbalances or improper placement also contribute significantly to browning. Excessive fertilization, known as fertilizer burn, introduces a high concentration of salts to the soil that draws water out of the root cells, leading to brown leaf tips and edges. Placing a sun-loving grass in deep shade or a shade-tolerant grass in intense sun can cause stress. Full sun exposure can scorch the tips of some grasses, while insufficient light can lead to premature leaf senescence. Transplant shock, a temporary wilting and browning immediately after moving a plant, is another common environmental stressor.
Biological Threats (Pests and Diseases)
Browning can also be the result of biological agents, specifically fungal diseases and insect pests, often encouraged by poor cultural practices. Fungal diseases thrive in conditions of high humidity and poor air circulation, often exacerbated by overwatering.
Rust, a common fungal infection, appears as small, raised spots or blisters on the blades that are typically yellow, orange, or reddish-brown, eventually causing the leaf to turn entirely brown or black. Leaf spot diseases are another fungal threat that produce distinct lesions on the foliage, causing the entire blade to die back. These diseases are best managed by improving air flow and watering the soil directly, avoiding wetting the foliage.
Pests like spider mites and aphids cause browning by physically feeding on the plant’s tissues. Spider mites suck the juices from the grass blades, leading to a stippled appearance that turns bronze or brown, often accompanied by fine webbing. Aphids are visible on the underside of leaves and stems, and their feeding also causes a loss of chlorophyll and eventual browning. Managing these pests often involves simple treatments like a strong jet of water or the application of an insecticidal soap.