A trash bag holder and expanding form is made from a sheet of stiff material that has at least three panels to hold a bag in an erect condition and to expand the opening of the bag into a shape that will allow the user to fill the bag with leaves or trash without having to hold the bag. The panels are separated by parallel, vertically disposed score lines that act as fold lines or hinges between the panels of the holder. The panels are stiff in character, because the invention is intended to hold the bag upright. The holder is formed from high density corrugated polyurethylene (HDPE) board, recycled plastic corrugated board or corrugated boxboard. The panels are proportioned so that the sheet material can be folded flat with the panels lying against one another. When the invention is folded into its operational configuration, the score lines act as corners such that the form takes a tubular shape with open ends. Retainers such as slits near a top edge of the form can be used to pinch and thereby lock the upper edge of the bag in place on the form.