Return of the Giant Hogweed

Every summer, Giant Hogweeds crowd the stream behind the platform at Thornliebank. They gestate for weeks, then flower, and only a week later start to sag. Then they die as quickly die as quickly as they burst into life, eventually leaving only skeletal stalks behind, some of which last into the next year, and the next crop.

(Extra points for guessing the reference in the title.)