When you come in from the garden, make sure mud doesn't come in with you. This mat is made of a coir, or coconut-fiber, doormat with boot brushes on each side. There should be at least 3 inches of clearance below your door so that it can open over the mat.
Find a sturdy mat, and gather push-broom heads to run along its short sides. Have a sheet of 1-inch-thick marine-grade plywood cut to size at a lumberyard; its width should equal the mat's, and its length should equal the mat's plus the width of the broom heads. Finish the plywood with marine-grade varnish. With a drill and screws, attach the mat to the plywood from above, and attach the broom heads to the board from below.