In My League: The Double-decker Square Foot Garden Box

Root plants that need more depth

My square foot garden boxes are only six inches deep. For most plants that's enough soil as long as the plants have adequate space around them to grow. The beauty of square foot gardening is the grid system that divides your garden into one-foot squares. If you are planting carrots, which only need about one inch spacing between mature plants, you can put sixteen carrots in one square. If you are planting leaf lettuce you put four plants in a square. For a large vegetable like cabbage or cauliflower you only put one plant per square.

But what about root vegetables, like carrots, that are longer than six inches? If your soil only goes down six inches that will stunt growth. I've planted two squares of carrots in six-inch deep soil. I plan to harvest them when they are still small. We like the baby carrots we get at the store and I thought this would be like having baby carrots.

There is another way to solve this problem. You can build portable, double-decker square foot boxes. It's just like building a four-foot by four foot garden box only on a smaller scale. For a portable square, I felt like two inch by six inch lumber was too big and heavy so I used one inch by six inch lumber cut into one-foot lengths. Once you've built the portable boxes you just place them on top of individual squares in your garden, fill them with Mel's Mix (developed by Mel Bartholomew in the All New Square Foot Garden) and plant as you would in any other square. Because the double-decker boxes are portable, you just move the box to a new square when it's time to rotate crops.

Here's the square for the carrots

I made two portable squares and I'm using one for carrots and one for potatoes. The carrot square I filled with soil and planted sixteen carrots. For the potato square I actually scooped out some of the soil from the original square, planted the potato eyes and just covered them with soil. As the green plants break through the surface I will add more soil and continue to do so until the double-decker box is full. This is supposed to encourage a lot of root growth and the potatoes are part of the root system.