Originally from the eastern Mediterranean region, sulfur cinquefoil was first reported in Washington State in 1937. It has since spread to most counties in the state including King County. It is invasive in grass fields or shrub-dominated areas. In King County, sulfur cinquefoil is most often found invading rocky or low-nutrient soils. It is found in pastures, roadsides, railroads, waste areas, and parks throughout King County. Plants are long-lived and highly persistent.
Most wildlife and livestock will avoid grazing this unpalatable plant due to its high tannin content and it will quickly become dominant in grazed areas. Even without grazing, sulfur cinquefoil out-competes forage grasses over time if unmanaged. Sulfur cinquefoil significantly reduces pasture productivity. Sulfur cinquefoil also invades Central Puget Sound prairies and out-competes native plant species.
Legal status in King County, Washington
Class B noxious weed. Property owners in King County are required to control this plant. For more information about noxious weed regulations and definitions, see Noxious weed lists and laws.
Sulfur cinquefoil has pale yellow (sulfur-colored) flowers with 5 heart-shaped petals. Stems are upright with some branching near the top, and up to 3 feet tall. There can be one to several stems per plant. There are numerous leaves on the stems, 5-7 leaflets with distinctly toothed edges. Distinguished by long, stiff hairs on stems and leaves that stick straight out from the surface. Look-alike native graceful or slender cinquefoil (Potentilla gracilis) has short hairs that lie flat on the stems and leaves and brighter yellow flowers. Sulfur cinquefoil seeds also have a net-like pattern on them, compared with the smooth seed coat of the native graceful cinquefoil.
Biology and reproduction
Sulfur cinquefoil is a perennial that spreads by seed and also reproduces vegetatively via new shoots emerging from the edges of its woody root crown. Over time, the stems sprouting from the central woody crown separate into individual plants, thereby expanding the population vegetatively. Plants can live up to 20 years in this way. The woody root crown renders mowing an ineffective control measure; the roots send up new shoots after mowing.
Sulfur cinquefoil begins growth in early spring, bolts and buds by May, and flowers from early May to July. Seed set is usually between mid-July and August and leaves often senesce in August but then green up again in the fall and continue to grow until an extended frost. Sulfur cinquefoil can self-pollinate and seedlings quickly mature into flowering plants.
Mowing is not effective. It can increase the population size by stimulating crown-sprouting and can spread the infestation if plants are already in seed. Digging is effective for small populations if the soil is moist and loose enough and if the majority of the woody root is removed. Repeated cultivation is also effective over time. Several herbicides are effective but may require repeat treatment and a suitable surfactant. See the PNW Weed Management Handbook for specific recommendations.
Additional information on sulfur cinquefoil
What to do if you find this plant in King County, Washington
Please notify us if you see sulfur cinquefoil growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. We map all known locations of regulated noxious weeds such as sulfur cinquefoil in order to help us and others locate new infestations in time to control them.
Sulfur cinquefoil photos - click thumbnail for larger image