Achenes shiny, brown to black. Pale smartweed , ladysthumb , and the foliage of swamp smartweed are killed by the first frost. Foliage turns brown to reddish and does not persist through the cold season. Rhizomes of swamp smartweed survive cold winter climates. Edges of ponds, shallow lakes, marshes, and streams, wet fields, areas subject to seasonal flooding, irrigation ditches, pastures, orchards, rice fields, grain fields, irrigated crops.
Plants typically grow in wet to moist soils, but tolerate periods of dryness.
Terrestrial plants grow best in disturbed places with fertile soils and minimal competition. Plants do not tolerate highly acidic soils. Often follows human disturbance and grows in moist urban places. Seed is dormant when shed and requires a cold, moist period to break dormancy. Seeds germinate in spring.