Famous Ideal Raised Garden Bed Depth References . A depth of 12 inches leaves plenty of room for soil so plant roots can grow freely. This article will take a look at some factors to consider when making your decision. How To Build a Simple Raised Bed Plant? Engineering Discoveries from www.pinterest.com Web when it comes to achieving gardening excellence, the optimal raised bed depth is your first step toward liberation from mediocre harvests. Raised beds can be any size, but depending on where you place one, depth is important. Before determining the ideal depth, let’s step back and review what strictly raised.