Yellow Sweetclover

Melilotus officinalis

Yellow Sweetclover (Melilotus officinalis) is a tall, sweet-smelling biennial from Europe and Asia, planted across the Plains for hay, pasture and soil building, with slender spikes of tiny yellow pea flowers. It blooms from June into September along roads, in pastures and on other open ground in the Black Hills. White Sweetclover (Melilotus albus), the same plant in almost every way except its white flowers, is covered here too.

Free photos from other sources

Yellow Sweetclover: Bright yellow pea flowers hanging along a slender spike — Melilotus officinalis. sophia_herrmeyer, CC BY 4.0, resized. Get it at the source

Yellow Sweetclover: Spike of small yellow pea flowers, the older ones fading pale — Melilotus officinalis. Jack Wander, CC0 1.0. Get it at the source

Yellow Sweetclover: Three toothed leaflets on a branching stem beside flower spikes — Melilotus officinalis. Jack Wander, CC0 1.0. Get it at the source

Yellow Sweetclover: Many yellow spikes rising from roadside grass — Melilotus officinalis. David LaMagna, CC BY 4.0, resized. Get it at the source

Yellow Sweetclover: A dense yellow stand filling an opening below pines — Melilotus officinalis. Jack Wander, CC0 1.0. Get it at the source

Yellow Sweetclover: White Sweetclover: long spikes of small white pea flowers above narrow toothed leaflets — White Sweetclover (Melilotus albus). Jason Leduc, CC0 1.0. Get it at the source

Yellow Sweetclover: White Sweetclover: a branch with several slender white flower spikes against a dark board — White Sweetclover (Melilotus albus). Jo Roberts, CC BY 4.0, resized. Get it at the source

Yellow Sweetclover: White Sweetclover: tall, airy white plants along a highway shoulder — White Sweetclover (Melilotus albus). Senna Bryce Robeson, CC BY 4.0, resized. Get it at the source

Quick facts
Family	Fabaceae · Pea
Status	Introduced biennial
Blooms	June through September, a few into October; White Sweetclover from July
Height	60–180 cm (2–6 ft)
Where	Roadsides, ditches, pastures, old fields, prairie dog towns, burns and other disturbed open ground
Also called	Yellow Melilot, Ribbed Melilot, Field Melilot, Sweet Clover, waȟpé swúla (Lakota)
Synonym	Trifolium officinale, Melilotus arvensis
Toxicity	Mold turns the plant's coumarin into dicoumarol, a blood thinner, and cattle that eat moldy sweetclover hay can bleed internally, abort or die; livestock eating mostly sweetclover can also bloat.
Traditional use	Gilmore (1919) wrote that the Dakota likened its smell to sweetgrass and hung bunches in their houses for the fragrance.
Note	This page also covers White Sweetclover (Melilotus albus, written Melilotus alba on older lists). USDA PLANTS lumps both under Melilotus officinalis.

Roots, seeds & germination

Root: A deep, semi-woody taproot with nitrogen-fixing nodules, measured over 1.2 m (4 ft) deep in the first year. Late in the first summer it stores food and forms crown buds that send up the flowering stems the next spring, and after flowering in the second year the whole plant dies.

Seed: Each small pod, 3–5 mm long, holds one seed about 2 mm long. A large yellow plant can make up to about 100,000 seeds, and many have a hard coat that lets them last for decades in the soil. Seeds travel in water, mud and hay and on animals and vehicles, one reason sweetclover follows roads.

Germination: Soft-coated seeds sprout readily, while hard seeds wait until the coat is scratched, heated or cracked by freezing and thawing. Most seedlings come up in spring, and fire often sets off a burst of seedlings from the seed bank.

How do you identify Yellow Sweetclover?

Crush a leaf or flower spike: sweetclover smells sweet, like fresh hay or vanilla. Dozens of tiny pea flowers, each 4–7 mm (¼ in), hang along slender spikes 5–15 cm (2–6 in) long on a tall, airy, much-branched plant, and the three narrow leaflets are toothed along most of the edge. White Sweetclover has white flowers, starts blooming a week or more later and is often taller, and its side petals are clearly shorter than the top petal. Alfalfa has larger flowers in short, rounded clusters, leaflets toothed only near the tip and coiled pods, and Black Medic is low and sprawling, with tiny yellow flowers in round heads.

When does it bloom?

June through September, a few into October; White Sweetclover from July.

Where does it grow?

Open, disturbed ground: road shoulders and ditches, railroad beds, pastures and hay meadows, old fields, mine spoil, prairie dog towns, burned areas and stream banks, often on limy or clay soils. A study at Wind Cave National Park found sweetclover tied to roads and trails, with yellow common in prairie dog towns and white on low, recently burned ground. The 1986 plant survey of Jewel Cave National Monument lists both, NPSpecies lists both at Wind Cave, Jewel Cave, Mount Rushmore and Devils Tower, and Black Hills herbarium specimens go back to 1908.