Bur Clover (Medicago polymorpha)

Bur clover is known by a number of names, including Medicago polymorpha, burr medic, and creeping burr. This legume is a green mulch, as it can correct nitrogen problems in soil, control erosion, and increase organic matter in the soil. It is an effective forage for sheep and can be used as an emergency forage if other crops fail. Bur clover carries the risk of becoming invasive.

I. Appearance and Characteristics 

Medicago polymorpha is a plant species of the genus Medicago. It is native to the Mediterranean basin but is found throughout the world. It forms a symbiotic relationship with the bacterium Sinorhizobium medicae, which is capable of nitrogen fixation. Common names include California burclover, toothed bur clover, toothed medick and burr medic.

This weedy forb is an annual broadleaf plant. It inhabits agricultural land, roadsides and other disturbed areas. It is found in lawns as well, where its burrs are able to cling to the clothing or fur of any species that pass near it, thus facilitating geographic spread via these seed capsules. It makes a poor lawn in the late summer, when the leaves have yellowed and fruit sets into the 7 mm seed heads that are covered with hooked prickles.

Burclover is a good forage for livestock, but the fruit is prickly. All classes of livestock, except horses and mules, can feed its leaves.

New seedlings have seed leaves that are oblong. The first true leaf is rounded. Later leaves will be tripartite, with a characteristic clover-like shape, appearing alternately on the stems. Leaflets have slightly serrated edges. The tiny yellow flowers attract small butterflies and other pollinating insects.

Full grown plant stems are up to 2 feet (60 cm) long, and usually sprawl along and/or under the ground. The stems often root at the nodes; adult plants, and even young plants that have been able to grow for a few weeks undisturbed can be very difficult to pull out, leaving behind tap roots and a network of plant pieces when pulled. Mechanically removing top growth from this plant will not usually eradicate it. If not properly managed, burclover may then become invasive and displace more desirable vegetation.

Being a member of the family Fabaceae, the flowers are clover-like, lipped and clustered. Bloom takes place from March to June in the plant’s native territory. Flowers (3–6 mm long) are small, bright yellow, and cluster into flower heads of 2 to 10 flowers at the stem tips. The fruit is a pod that coils tightly 2 to 6 times and has rows of prickles on the outside edge of the pod.

The fruits are about 6–7 mm across. They start out green and relatively soft, but quickly turn brown and hard. Inside the pod are several seeds—usually yellow or tan and kidney-shaped. The burred fruiting bodies can be quite difficult to remove from softer fabrics, such as fleeces and knitted socks.

II. How to Grow and Care

Bur clover is a low-maintenance plant that thrives in a variety of soil types and environmental conditions. Special care points include ensuring adequate sunlight and periodic watering, as bur clover tolerates drought but performs best with consistent moisture. Regular monitoring for weed competition is important, as bur clover can be crowded out by more aggressive species.

Sunlight

Bur clover flourishes under full sun, thriving with an abundance of direct sunlight for robust growth and optimal health. Despite a preference for radiant conditions, it demonstrates a remarkable resilience, tolerating a spectrum from partial sun to full shade. This adaptability allows bur clover to acclimate to varied light environments, albeit with potential differences in vitality and development.

Outdoors, bur clover is best positioned in locations that receive unfiltered sunlight. The absence of a mention of indoor cultivation suggests bur clover is typically favored for outdoor planting, where it can achieve its full potential in the right light conditions.

Watering

Originating from regions with a Mediterranean climate, bur clover has adapted to survive periods of dryness, showcasing moderate drought tolerance. In its native habitat, it experiences wet winters and dry summers, requiring it to efficiently manage water retention.

Consequently, bur clover thrives in conditions where watering is consistent but not excessive, necessitating watering every week to maintain optimal hydration. This species prefers well-draining soil that allows for proper moisture balance without waterlogging the roots. As an herbaceous plant commonly grown outdoors, bur clover’s growth cycle is significantly influenced by rainfall patterns, making seasonal adjustments to watering schedules essential to mimic natural precipitation cycles.

Fertilizing

Fertilizing bur clover bolsters its vigour, particularly during its active growth in spring. Utilize balanced nutrition fertilizers (e.g., 10-10-10) biweekly, decreasing frequency in summer. Boost bur clover’s early growth with a high nitrogen formulation; however, moderation is key—over-fertilization may harm bur clover. Practice careful application, ensuring fertilizer doesn’t clump on foliage. Seasonal needs vary; minimal fertilization in winter. Accurate dosing is crucial; typically, a teaspoon per plant suffices. Assess soil quality first—bur clover thrives with targeted feeding.

Propagation

The preferred propagation method for bur clover is sowing seeds in Spring. This plant propagates easily, showing successful signs of germination with emerging seedlings. Ensure well-draining soil and consistent moisture for optimal growth.

Transplanting

For bur clover, the prime transplanting window is mid to late spring into early summer, when temperatures foster root establishment. Choose a sunny to partially shaded location, with well-draining soil. Light watering post-transplant ensures a strong start for bur clover.

III. Uses and Benefits 

• Culinary uses

The plant is edible and consumed as a vegetable in China, primarily in Jiangsu, Zhejiang and Shanghai. Its Chinese culinary names include 草頭 (Wu tsho-doe, Mandarin Pinyin cǎo tóu), 金花菜 (Wu cin-hau tse, Mandarin Pinyin jīn huā cài), 三叶菜 (sān yè cài) and 秧草 (yāng cǎo), while 南苜蓿 (nán mùxu) is its scientific name. It is also consumed in indigenous Otomanguean communities in Southern Mexico. In the Triqui language it is known as kkweej chakáj, meaning ‘edible green (of the) pig.’