Jewish law requires the ritual washing of the hands before eating bread. This washing is accompanied by a blessing. But why do we wash before eating the green vegetable and why in this case is no blessing recited?    

Fruits or vegetables dipped in water can acquire ritual impurity (Lev. 11:34). Washing before eating vegetables which have come into contact with water is a hold-over from Talmudic times. In that period many Rabbis attempted to eat all their foods in a state of ritual purity – trying to experience in their daily eating the sense of sacredness associated with the Temple. To emphasize that this is only a pious custom, and not even a rabbinic requirement, no blessing is recited.     

Except for the seder night the custom has fallen into general disuse, even among the strictly observant. But on seder night we wash at the beginning of the evening to create the spirit of a sacred gathering conducted in purity and devotion.

haggadah Section: Urchatz
Source: A Different Night