Melilotus officinalis (Yellow Sweet Clover)
| Also known as: | |
|---|---|
| Genus: | Melilotus |
| Family: | Fabaceae (Pea) |
| Life cycle: | annual, biennial |
| Origin: | Europe |
| Status: |
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| Habitat: | part shade, sun; disturbed soil; fields, prairies, roadsides, railroads, gravel pits, empty lots, shores, river banks, woodland edges |
| Bloom season: | June - September |
| Plant height: | 2 to 6 feet |
| Wetland Indicator Status: | GP: FACU MW: FACU NCNE: FACU |
| MN county distribution (click map to enlarge): |  |
| National distribution (click map to enlarge): |  |
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Detailed Information
Flower: 
![[photo of flowers]](/udata/r9ndp23q/yellow/melilotus-officinalis-yellow-sweet-clover_0621_151312.jpg)
Flowers are clustered in spike-like racemes up to 6 inches long on branching stems, arising from leaf axils, and at the top of the plant, each with 20 to 50+ flowers. Flowers are yellow, ~¼ inch (4 to 7 mm) long, pea-shaped, the upper petal (banner) flaring up, the lateral petals (wings) about as long as the banner. The calyx cupping the flower is light green with 5 narrowly triangular lobes about as long as the calyx tube. Flower stalks about as long as the calyx tube.
Leaves and stems:
![[photo of leaves]](/udata/r9ndp23q/yellow/melilotus-officinalis-yellow-sweet-clover_0713_102527.jpg)
Leaves are alternate, compound in groups of 3 on a stalk about 1 inch long. Leaflets are 3/8 to ~1½ inches (1 to 4 cm) long, up to ~½ inch (to 15 mm) wide, variably shaped from nearly diamond-shaped to oval-elliptic to lance-oblong, rounded to flattened at the tip, wedge-shaped at the base, green to blue-green or gray-green. Edges are toothed, surfaces mostly hairless. At the base of the compound leaf stalk are a pair of appendages (stipules) up to 3/8 inch (1 cm) long, lance to awl-shaped, those on the lower stem sometimes toothed at the base. Stems are usually much branched, may be ridged or grooved, are mostly hairless and green or sometimes tinged red. Plants can grow tall and spindly or shorter and bushy.
Fruit:
![[photo of developing fruit]](/udata/r9ndp23q/yellow/melilotus-officinalis-yellow-sweet-clover_0713_102311.jpg)
Fruit is an oval pod 3 to 5 mm long with a bit of the style persisting at the tip, the surface irregularly covered in elongated ridges/veins, the space between them typically longer than wide. Each pod contains 1 or 2 seeds about 2 millimeters long that ripen to yellowish brown.
Notes:
Like the closely related White Sweet Clover (Melilotus albus), Yellow Sweet Clover was brought to North America as a forage crop and quickly escaped cultivation. It is commonly found in the disturbed soils of roadsides, old fields, trail edges and empty lots, but also encroaches in high grade habitat and can have explosive growth following fire disturbance.
The most obvious difference between the two Sweet Clovers is flower color, with Yellow starting to bloom a couple weeks earlier than White, but when flowers are not present these two are very difficult to distinguish, relying on the texture of mature pods (Yellow=elongated ridges/veins vs. White=shorter ridges/veins). But I have to wonder if it really matters which one you have? Both are ubiquitous in Minnesota and equally problematic in natural areas.
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More photos
Yellow Sweet Clover plant
Yellow Sweet Clover plant
roadside Yellow Sweet Clover
an infestation of Yellow Sweet Clover
Yellow Sweet Clover plant
Yellow Sweet Clover plant
roadside Yellow Sweet Clover
an infestation of Yellow Sweet CloverPhotos by K. Chayka taken in Ramsey and Red Lake counties. Photos by Peter M. Dziuk taken in Anoka County.
Comments
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2008-06-18 22:43:22
This grows in St. Paul along the railroad tracks. I guess it must grow lots of places to be a noxious weed. However you should mention that when it is mowed it has a heavenly scent.
on: 2012-06-04 20:48:12
Bummed. I bought sweet clover to grow for my honey bees and was looking into how tall it gets and also found out it's considered an invasive species here in Minnesota! So now what do I do with 7# of sweet clover?! :( See if the place I bought it will take it back I guess...
on: 2018-08-16 05:11:49
My dad actually has a picture of me and my brother in front of our pasture out in Goodridge, MN that had become completely infested with them. They towered over us both. The smell is nostalgic. I have seen plenty of them in Red Lake Falls along the trails as well as taking over the roadside entering town.
on: 2023-06-29 23:36:00
Found a single plant in grassy/weedy area between barn and cultivated field. In bloom today. Root is one single taproot with very few hair-like small roots coming off. Easy to pull out, ground fairly dry.
on: 2024-06-13 13:57:49
This grows all along I-94, as well as other major highways in the twin cities. An important part of understanding an invasive plant is knowing why it is invasive. Like garlic mustard, white and yellw sweetclovers are biennials that are easy to pull, but they have massive, long-lasting seedbanks and are allelopathic (meaning that the create toxins which poison the soil and prevent anything else from growing). Additionally, it outcompetes many natives.
For these reasons, when found growing in healthy native communities it should be managed by hand pulling - ideally in the early spring before the second year flowers have developed, or the fall after the first-year root-crown buds have developed. You can also pull in the summer if the soil is sufficiently moist. Fall pulling will do the least damage to native neighbors, however.
In large monocrops, the best treatment is amine 2,4-D. Mecamine (2,4-D with Dicamba) is particularly effective.