Is there an ideal size for a raised bed?
Several factors dictate size, including soil conditions, space limitations, and considerations of physical comfort.
Length and Width. When figuring the dimensions of the raised bed frame, first consider a garden’s space constraints (don’t forget to leave room to walk around the bed). Second, assess your reach. It is vital to be able to reach the center of the bed from either side to avoid stepping on the bed, which compresses the soil. For most people, this means limiting the width to about 4 feet. If your bed is only accessible from one side, limit the width to a maximum of 3 feet. Length is limited only by the size of your garden and by building materials.
Height. Most raised beds range from 6 to 12 inches, with some as high as 36 inches. In general, the worse the underlying soil, the deeper you will want a bed to maximize the amount of good soil available to plants. And, more depth means more room for roots to grow. Deeper beds hold more soil and, thus, more moisture, reducing watering needs. Remember that the taller the sides, the more pressure the weight of the soil places on them. You may need to compensate with thicker wood or cross supports to prevent the wood from bowing.
For more of Art’s kitchen garden tips, see Ask the Expert: How to Create a Beautiful Edible Garden.
What is the best material for raised beds?
Raised beds are traditionally made using naturally rot-resistant cedar. But, honestly you can build the bed wall with almost any material that will contain the soil, including stone, woven willow, and concrete. For vegetable and herb gardens it is important to avoid using pressure-treated lumber, which can leach heavy metals into the soil. Untreated, naturally rot-resistant lumber is the gold standard of building materials.