Common name: roundhead leek, drumstick allium, ballhead onion
Allium sphaerocephalon has tall stems, with small egg-shaped flowers that come out mid-summer. The flowers change colour from green to red as they come out. They are found at the northern end of the Laburnum Walk.
Flower photos from Garden display.
Seed pod photo from Travis Owen, Pacificbulbsociety.org
Dried flower photo by Agnieszka Kwiecień via Wikimedia Commons