A yard of burlap will make a number of pictures, depending on size. Buying half-yard pieces in several colors will provide variety. Not all colors will compliment all seeds. Light-colored seeds such as cucumber and pepper will not show up as well on a beige background as they would on a darker color. Mimosa and apple seeds won t stand out on brown.
Light green is a good neutral color.
A lightweight board or a discarded piece of Masonite something that won t bend is recommended for a stiff backing. Cardboard is undesirable, as it will soon buckle. If you have a friend who has a woodworking shop, you re in luck, as there are usually scrap pieces of wood lying around that are free for the asking. I suggest keeping your first picture simple in order to learn the basics. Be sure that board is clean of all dust, and cut the burlap so that it is slightly larger than the board.