Clover (Trifolium species) is prized in lawns and gardens for its low maintenance and ability to enrich the soil. Homeowners often use white clover (Trifolium repens) or micro-clover as a ground cover or mixed with turfgrass. As legumes, these plants form a symbiotic relationship with Rhizobium bacteria, converting atmospheric nitrogen into a usable form. This natural process reduces the need for synthetic fertilizers. When clover patches begin to yellow, wilt, or disappear, it signals a problem requiring diagnosis, differentiating between physical stress, biological attacks, and chemical exposure.
Environmental Stressors
The most frequent reasons for clover decline are non-biological, stemming from issues with water, light, or soil structure. Clover is generally drought-tolerant, but prolonged lack of water causes wilting and rapid browning. This leaves the plant’s stolons exposed to direct sunlight, which increases ground temperature and causes further damage.
Conversely, overwatering or poor drainage leads to damaging conditions like root rot. Saturated soil deprives roots of necessary oxygen, which is especially problematic for red clover (Trifolium pratense) due to its low tolerance for waterlogging. Signs include yellowing leaves and lack of vigor, which requires inspecting soil moisture to differentiate from drought stress.
Clover is a cool-season plant that prefers temperatures between 50 and 85 degrees Fahrenheit and is sensitive to extreme heat. Summer heat stress suppresses growth and increases moisture loss, compounding drought effects. While clover tolerates light shade, it will not thrive in dense shade, often leading to thinning stands and die-off if planted under thick canopies.
Physical soil conditions also play a role, as heavily compacted soil restricts the ability of clover’s roots to grow and spread. Dense soil limits water infiltration and oxygen exchange, creating an anaerobic environment. This prevents the plant from absorbing necessary nutrients and moisture, resulting in stunted growth and an unhealthy appearance.
Pests and Pathogens
Clover is susceptible to biological threats, including fungal diseases and insect pests that cause significant damage. Fungal pathogens often thrive in cool, damp conditions and are a common cause of widespread decline. For example, Sclerotinia Crown and Stem Rot, caused by Sclerotinia trifoliorum, creates tiny brown spots that merge into a mass of rotting plant material.
Another common fungal issue is Rust, caused by species in the Uromyces genus, which presents as orange or reddish pustules, particularly on the underside of leaves. These pustules reduce the leaf’s ability to photosynthesize, weakening the plant and causing leaves to yellow and wither prematurely. Powdery mildew is also visible as a fine, white or gray dusting on the upper leaf surface, which causes infected leaves to turn yellow and wilt.
Insect pests can directly attack the plant structure, causing visible damage or slow decline. The Sitona weevil is identified by the semi-circular sections it removes from the edges of the clover leaves. Pests like the Clover Root Weevil attack the root system, reducing the plant’s ability to absorb water and nutrients. This results in overall wilting and stunting often mistaken for simple drought stress.
Soil Chemistry Imbalances
Clover’s nitrogen-fixing ability means it has specific soil chemistry requirements that differ from turfgrass. The plant performs best in a slightly acidic to neutral soil pH, ideally ranging from 6.0 to 7.0. A low pH significantly inhibits growth, reduces essential nutrient availability, and hinders the survival of the Rhizobium bacteria necessary for nitrogen fixation.
While clover fixes its own nitrogen, it requires sufficient levels of other macronutrients, particularly phosphorus (P) and potassium (K). Phosphorus deficiencies lead to stunted growth and poor root development, while low potassium affects the plant’s overall health and stress resistance. Soil testing is the only way to accurately determine these imbalances and guide the application of lime or specialized fertilizers.
Paradoxically, excessive nitrogen is also a problem, especially when high-nitrogen fertilizers intended for grass are applied. High nitrogen levels actively suppress clover, a nitrogen-fixing legume, giving grass a competitive advantage. This nitrogen can also cause “fertilizer burn,” manifesting as yellowing or browning of leaves and stems due to high salt concentration drawing moisture out of the plant cells.
Accidental Herbicide Exposure
A common and often sudden cause of clover death is accidental exposure to lawn weed killers. Clover is a broadleaf plant, and nearly all herbicides designed to eliminate weeds like dandelions are formulated to target broadleaf species. Therefore, applying a broadleaf herbicide will severely injure or kill the clover alongside the intended weeds.
Exposure often occurs through wind drift, where the herbicide mist travels from a treated area onto the clover patch, or from residual chemicals left inside equipment. The symptoms of this chemical damage are highly distinct and typically appear as severe distortion of the plant tissue. Affected clover shows twisted stems, curled or cupped leaves, and an abnormal growth pattern, leading to sudden, widespread decline.
Herbicides containing synthetic auxins, such as 2,4-D, are notorious for causing these visual cues. They mimic plant growth hormones but force uncontrolled, chaotic growth that quickly kills the plant. Since clover is killed by the same products used to control other broadleaf weeds, care must be taken to only use selective herbicides that spare legumes or rely on non-chemical weed control methods.