Crimson clover, scientifically known as Trifolium incarnatum, is a highly valued annual plant primarily used in agriculture and gardening circles. It belongs to the legume family, which gives it the unique ability to significantly improve soil health. Gardeners and farmers commonly use this plant for its striking appearance and its practical benefits below the soil surface. This species is a familiar sight in fields and along roadsides, particularly in regions with milder winters. Crimson clover provides a multitude of benefits, making it a popular choice for sustainable farming practices and home gardening.
Identifying Characteristics and Origin
This distinctive plant is an upright annual herb that typically grows to a height between one and three feet, featuring a slightly hairy stem and trifoliate leaves with rounded tips. The most recognizable feature is its flower, which forms dense, elongated, cone-shaped heads, generally measuring two to three inches long. These flower heads display a brilliant, deep crimson or scarlet color, which is reflected in its common name and its species epithet, incarnatum. (3 sentences)
The species epithet, incarnatum, is Latin for “flesh-colored” or “blood-red.” The plant is native to Southern Europe and Western Asia Minor, where it has been cultivated for centuries. It was introduced to the United States as a cultivated crop in the mid-1800s, where it quickly became naturalized across much of North America. Crimson clover is a cool-season annual, meaning it germinates, grows, flowers, and dies within one year, with its most vigorous growth occurring during cooler periods. (4 sentences)
Role as a Cover Crop
Crimson clover’s primary function in modern agriculture is as a winter annual cover crop, which is a plant grown specifically to manage soil health rather than for harvest. Its most celebrated benefit is its capacity for nitrogen fixation, a process performed through a symbiotic relationship with Rhizobium bacteria living in nodules on its roots. These microorganisms convert atmospheric nitrogen gas (N₂) into a form plants can readily use, such as ammonia (NH₃), which is then released into the soil as the plant residue decomposes. (3 sentences)
This nitrogen contribution can range from 70 to 150 pounds per acre, depending on the growing conditions and when the crop is terminated. By fixing nitrogen, the clover acts as a natural, sustainable fertilizer for the subsequent cash crop, reducing the need for synthetic nitrogen applications. The plant’s dense, rapid growth also helps suppress the emergence of weeds by physically shading the soil and competing for resources like water and nutrients. (3 sentences)
The extensive root system of the clover helps to bind soil particles together, which is highly effective at preventing soil erosion, especially during dormant seasons or heavy rainfall. Furthermore, the plant’s beautiful, bright red flowers are a significant draw for beneficial insects, including bees and other pollinators, contributing to local biodiversity. It is also utilized as a high-protein forage crop for livestock, often providing approximately 14 to over 25 percent crude protein depending on the stage of harvest. (3 sentences)
Cultivation and Management
Crimson clover is typically sown in late summer or early fall, about six to eight weeks before the first expected frost date, to establish itself before winter. This timing allows the plant to survive the winter as a small rosette and then resume rapid growth in the spring. It grows best in well-drained, loamy soils but is notably tolerant of moderate acidity and a variety of soil textures. (3 sentences)
Planting depth is shallow, usually between one-quarter and one-half inch, and good seed-to-soil contact is necessary for successful germination, which generally occurs quickly with adequate moisture. Optimal seeding rates vary, but a common range for drilling is 15 to 18 pounds per acre, or slightly higher for broadcasting. The plant requires moderate moisture to thrive, particularly during establishment. (3 sentences)
Management involves a practice called “termination” before planting the next crop, which means killing the clover to transfer its stored nitrogen and organic matter into the soil. To maximize the nitrogen benefit for the following cash crop, the clover is often terminated by mowing, tilling, or using herbicides just after it begins to flower. This timing is when the plant has fixed its maximum amount of nitrogen. Terminating the clover before it sets seed is also important to prevent it from becoming a weed in future seasons. (4 sentences)