Black medic (Medicago lupulina) is a member of the legume family of plants, and its foliage and flowers both resemble those of clover. When growing as a lawn weed, black medic is usually first noticed when it blooms.
Black medic in bloom. Photo via Adobe Stock.
Identification
- Growth habit: short and sprawling, with trailing stems (which do not root as they creep) and a taproot; the root system has small nodules of nitrogen-fixing bacteria
- Flowers: yellow, clover-like clusters, growing out of leaf axils
- Leaves: divided into 3 leaflets, similar to clover, but with the center leaflet on a short stalk compared to the other two leaflets that connect directly to the petiole (leaf stem)
- the tip of each leaflet ends in short but distinct point
- the base of the petiole is flanked by stipules (in this case, triangular or oblong leaf-like flaps)
- alternate leaf arrangement
- Stems: hairy
- Seeds: contained in a kidney-shaped black pod
Small yellow flower clusters resemble clover. Each individual flower in the cluster is only a few millimeters across.
Flower clusters arise from the leaf axils (where leaves join the main stem), and the leaf arrangement on the stem is alternate. Leaf tips come to a single point, and the middle leaflet has a visible stalk whereas the side leaflets attach directly to the petiole (leaf stem).
The central leaflet of black medic's 3-part leaves has a noticeable stalk, whereas the side leaflets attach directly to the petiole. At the base of the petiole are stipules. The stem is hairy.
The wrinkly, kidney-shaped seed pods ripen from green to black.
Similar species
The following species with 3-part leaves may be confused with black medic at first glance.
| Common Name | Botanical Name | Traits Shared with Black Medic | Traits Different from Black Medic |
|---|---|---|---|
| Yellow Woodsorrel | Oxalis stricta and Oxalis corniculata | Clover-like foliage; yellow flowers | Leaflets lack a pointed tip, and all 3 are attached directly to the petiole; distinctly 5-petaled, open flowers; creeping rhizomes |
| Common Lespedeza | Kummerowia striata / Lespedeza striata | Tiny pointed tips on each leaflet; sprawling growth habit | Leaflet shape is more narrow, and leaves have prominent, angled, parallel paler veins; single flowers (not in clusters) are pink and white |
| White Clover | Trifolium repens | Short, wide growth habit | Leaflets are all attached directly to the petiole; leaflets often have a pale chevron marking in their center; flowers are white or slightly pinkish |
Life cycle and reproduction
Black medic is typically a summer annual: seeds germinate in spring, the plants grow and bloom in summer, and ripen seeds prior to dying by autumn. Annual plants have a one-year life cycle. Occasionally, black medic will behave as a winter annual (germinating in autumn) or as a biennial (two-year life cycle).
Black medic spreads by seed.
Conditions that favor growth
Most often noticed in lawns, black medic favors sunny, dry areas with sparse, struggling turfgrass. It more easily out-competes turf in areas of low soil nutrients, such as under-fertilized lawns with insufficient nitrogen. It can also grow in areas with little to no mulch and exposed soil, or in compacted soil like in the joints between walkway pavers.
Black medic management in lawns
General lawn care practices that discourage weeds
Maintain healthy, dense turf that can compete with weeds and prevent weed germination and establishment. Fertilize the lawn as recommended (based on season and turf type), mow high, and overseed cool-season lawns each autumn to keep the lawn dense and better able to crowd-out seedling weeds. Core-aerate to reduce soil compaction. Learn about fertilizing, mowing, overseeding, and aeration in the resource: Maintaining an Established Lawn.
Mechanical management
Remove black medic plants (including the central root system) by hand or with a manual weeding tool. Doing this when the soil is moist makes the task easier. Pulling up or digging out individual plants is a viable option at the beginning of an infestation (when the plants are not yet abundant) and for young annual bluegrass plants.
Manage Weeds Without Chemicals
Chemical management
Herbicide use should always be a last resort when managing weeds. Check for any local pesticide restrictions before buying and applying a product. For example, the Montgomery County pesticide law does not allow most synthetic pesticides (which includes herbicides) to be used on lawns. The active ingredient glyphosate is also prohibited on lawns in Baltimore City.
Learn about herbicide classifications and terminology:
Herbicide Options for Managing Common Lawn Weeds
Post-emergent herbicide
Spot-treat individual black medic plants or infested areas with a liquid broadleaf herbicide applied when the weeds are actively growing. Look for a product with one or more of the following active ingredients: 2, 4-D, MCPP (mecoprop), dicamba, or triclopyr. An application of non-selective herbicide may work, but would also damage any turfgrass exposed to the herbicide.
CAUTION: Do not spray herbicides containing dicamba over the root zone of desirable trees and shrubs. Roots or leaves may absorb this ingredient and be substantially damaged. Refer to the product label for other precautions.
Reference
Neal, J.C., Uva, R.H., et. al. (2023). Weeds of the Northeast. (Second edition.) Comstock Publishing Associates.
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