Gardeners with heavy, clay, or even tainted soil might consider constructing a raised bed outlined with durable, untreated lumber. The boxed bed is then filled with a perfect, lightweight mix of topsoil, compost, and leaf mold. Other small-space gardeners who choose containers to grow their veggies and herbs can use this same mix for their pots. Any gardener who suspects the soil is contaminated should have a soil test taken prior to growing edible plants. This is best done when the soil temperature is above 50 degrees.