I'm going to assume you mean Verbena. I have two types; Verbena hastata, which is tall with tall seedheads, and Verbena bonariensis, which have smaller seedheads. Personally, I like using tissue boxes or large plastic pretzel containers. Just put the spent heads in, shake the box or container around, and the seed comes out of the heads. You'll get chaff out with the seed, so if you're going to trade, just make that known up front. If it's the short annual verbena, I can't help...