You don't have to fill the entire 6'x6' Keyhole composting garden with topsoil. You can create your own organic soil by using compostable yard waste and cardboard (including the box the garden comes in!). Simply alternate between layers of brown and green materials, making sure to water generously in between each layer. Top with 6-8 inches of topsoil to finish it off. Over time the collection of materials will break down to create the black gold of gardening - composted soil.