The depth of your raised bed depends on what you want to grow and what is underneath. If you already have decent garden soil, you can get away with a shallower bed, say 5-6 inches deep, since larger crops like tomatoes will send roots into the ground below. The same is true of root crops like carrots and beets. If you’re setting up your raised bed over a lawn or weedy area, I recommend that it be at least 10 inches deep. To avoid back-breaking bending, the bed should be about two feet high with a six-inch wide sturdy edge. That way you can sit on the side of the bed and garden in comfort.
The size and shape of the bed are dependent on the lay of your land as well as the garden design you wish to achieve. In any case, four feet is the maximum width for a comfortable reach-across bed. Mine are four, six and eight feet long. Any longer and the walk around would be too cumbersome. Leave at least two feet between beds for wheelbarrow or garden cart access.
Good soil is the single most important factor in growing a successful garden. With a raised bed you don’t have to worry about what’s underneath. Simply set up the bed, fill it with a fertile blend – I use half Pro-Mix (a peat-based soilless mix with vermiculite and perlite) and half compost. If you purchase compost, try to find an organic source. I also add rock powders – greensand and rock phosphate – to my beds as a source of trace minerals. To find out how much you will need to fill a specific bed, google “soil calculator”, and you will find an online tool to provide the answer.
An irrigation system installed at the time you assemble your raised beds will save you a world of work and give you larger and more flavorful yields. I prefer a drip system because it is water-saving and delivers moisture right where it’s needed – to the plants’ roots – thereby avoiding problems caused by wet foliage.
Check out our Raised Garden Bed Review for more information on some popular raised garden beds you can purchase.