Some Undesirable Plants in the Washington Park Arboretum Display Beds

Equisetum arvense (commonly known as “horsetail”) is native throughout the temperate and arctic areas of the northern hemisphere – any place with wet or damp soil with some sunlight.
Colonization relies heavily on its extensive, deeply-penetrating creeping root system and to a lesser extent, on spore production. During the winter, the foliage dies to the ground.
Horsetail provides habitat and protection of wildlife creatures and excellent erosion control.
Since Horsetail does not respond to nitrogen fertilization and wants sunlight, its growth can be suppressed through the use of fertilizers and competitive cover crops. Other control options include applying inorganic mulches, weed barrier fabrics, or repetitive regularly scheduled tillage or mowing over at least a two-year period. Cutting new growth prior to it reaching eight inches is most effective.

Creeping Buttercup is a low-growing perennial that spreads by stolon (runners) as well as by seed. It blooms from March to August. A single plant can cover 40 square feet (five foot X eight foot area) in one year.
This perennial plant provides good erosion control and bright yellow flowers that are attractive to pollinating insects. However, it can crowd out smaller less robust plants.
Non-chemical control usually requires manual removal of the plants and their roots using a soil knife. Line-trimming large areas affected by Buttercup, followed by heavy mulching afterwards will yield good results for future control efforts. Regular management of the area is necessary to fully eliminate this plant.

Wood Avens is a short-lived, Eurasian perennial that can be found in any kind of shaded habitat.
Plants rely on seeds for reproduction. Flowers are replaced by spheroid bundles of seeds with hooked tips, allowing them to cling to fur, bird feathers, and clothing of humans to transport themselves.
Non-chemical control can be achieved by line trimming or mowing to cut down plants during the flowering stage to prevent seed development,

Herb Robert is both a winter and a spring annual or biennial. It is a low-growing plant that is hairy and shallowly-rooted, growing in moist forests or dry rocky outcrops. Plants have a pungent odor when crushed.
Reproduction is by seed that is ejected in response to drying of the seed capsule. Reports indicate that they may be ejected as far as 15 to 20 feet from the mother plant.
Non-chemical control can be achieved by hand pulling plants before they go to seed. Seeds can survive in the soil for a number of years, so frequent monitoring and control is needed. Mow or cut back with a line trimmer early in the season before they flower.

Native to Europe, Creeping Thistle is an aggressive perennial with a vigorous root system that continually produces new shoots, invading new areas and out-competing other vegetation types.
Creeping Thistle spreads primarily by rhizomes and seeds.
Mowing or cutting of stands prior to flowering in late June can significantly reduce the overall seed production of a population. However, Creeping Thistle will continue to flower after mowing, so repeated attempts must be made throughout mid and late summer to prevent overall seed production. Multiple years of regular cutting of emerging plant crown is usually necessary to eliminate this plant.

University of Washington Botanic Gardens