Sforno on Genesis 2:6/ספורנו על בראשית ב׳:ו׳

1ואד יעלה מן הארץ, on the day they were completed, i.e. at the end of the sixth “day” a vapour rose from the earth equivalent to beneficial dew which irrigated the earth and enabled it to bring forth further vegetation without the help of rain or man’s labour.