The elm’s graceful vase-shape made it a popular shade tree for city streets. Although elms have been hit hard by Dutch elm disease over the last century, says Dr. Levetin, "it is still an important tree is many parts of the country, [so] we still see a lot of elm pollen in the air."
When does it peak? February to April (white elm or American elm), some species flower in the fall
Where does it grow? Eastern and Central United States