collecting american elm today. the viability stays up there if you collect it right after dropping, air dry thoroughly and refrigerate. elm is unusual because it drops in june, and the seed can germinate right away, within a week. so if there's some rain, all the seed is gone within a week. year old seed I've test still has a good germination rate. should you plant elm? I don't know, it's hard to be down on a whole genus, american elms are nice trees and can get large even in areas where there is dutch elm disease. If you don't have a tonne of elm around then the disease pressure will be very minimal. It's both things, the city here isn't planting new elms, but there are plenty of old ones and they're nice shady trees.