Named after Timothy Hanson, an American farmer who popularized it in the 1720s, timothy grass is now widely grown as a forage and hay crop in the U.S. It's also one of the worst early-summer grass allergens, behind only orchard grass, according to Pollen Library.
Habitat: Native to Europe and Asia, and adapted to cool, humid parts of North America
Description: Perennial grass with flat leaves, grows 2 to 4 feet tall
Allergy season: June to July
Tips: As with other grasses, timothy grass pollen can be controlled by mowing the plants before they flower. The species isn't heavily grown in urban areas, but it does cross-react with pollen from other grass species.