Fireweed occurs in open woods and along streams. Fireweed is well adapted to disturbed areas such as cut-over or burned forests and swamps, avalanche areas, recently deglaciated areas, and riverbars. Additional disturbed sites are highway and railroad rights-of-way, waste places, and old fields. It is especially abundant following fire.

An erect, generally unbranching forb, growing up to 9 feet tall. It has fine roots and rhizomes. It flowers June to September, and reproduces from seeds and rhizomes.