Yellow sweet-clover

Yellow sweet-clover (Melilotus officinalis)

Herbaceous biennials. First-year plants do not bloom. Second-year plants grow 3-5’ high and are bush-like. Erect stems are multi branched and often hollow.

Overview

Other names for this plant include:

  • Common names: white sweetclover, yellow trefoil, yellow melilot, common melilot
  • Scientific names: Melilotus alba; M. arvensis; M. leucanthus; M. lutea; M. officinalis var. micranthus

Ecological threat:

  • Invade prairies, savannas, dunes, roadsides, and abandoned fields.
  • Fire stimulates germination of sweet clover seeds and can exacerbate invasions.

Classification in Wisconsin: Not regulated.

Identification

First year plants: Leaves are alternate, oblong, tri-lobed leaflets are finely-toothed. The terminal leaflet is on its own petiole.

Second year leaves: Alternate, with 3 finely-toothed leaflets, and clover-like but longer (1”) and thinner (1/3”) than other clovers. The middle leaflet grows on a short but distinct stalk.

Flowers: Five-parted, small, yellow, fragrant, pea-like flowers, clustered in dense racemes. Second-year plants bloom late spring through summer.

Fruits & seeds: One or two small seeds with hard seed coats produced per flower; up to 350,000 seeds per plant. Seeds remain viable in the soil for up to 30 years.

Roots: Strong taproot and extensive lateral roots.

Similar species: White sweet clover (Melilotus alba) is usually taller and has white flowers that bloom later.

Distribution

Known county distribution of yellow sweet-clover
Counties in WI where yellow sweet-clover has been reported (as of July 2011). Both vouchered and unvouchered reports included.

Do you have yellow sweet-clover in your county but it isn't shaded on the map? Send us a report.

Control

Mechanical: Hand pull small populations before seed set. Use brush-cutter for large populations. Late fall burn to stimulate germination followed by a late spring burn next season to eliminate second year plants before seed set.

Chemical: Spray seedlings with 2, 4-D (LR) in early spring.

Photos

View yellow sweet-clover pictures in our photo gallery!

Resources

Sources for content:

  • Czarapata, Elizabeth; Invasive Plants of the Upper Midwest: an illustrated guide to their identification and control. University of Wisconsin Press. 2005. Pg. 68-70
  • USDA Forest Service, Northeastern Area Forest Health Staff. Weed of the Week: Yellow Sweetclover [exit DNR].

Links for More Information

Last revised: Wednesday December 19 2012