Helianthus annuus. Plant these and stand back! In a fertile garden these will grow to 12 feet and you'll need a saw to cut down the stalks in the fall. I cut down the mature heads and lay them out in an open area for natural flat birdfeeders. These will reseed in the garden, but can be started indoors for earlier blooms. The birdies will drop seed in the strangest places, including your neighbour's yard. Makes an excellent temporary fence or windbreak.