So many people recommended a book called Square Foot Gardening by Mel Bartholomew that I had to give it a read. This photo shows my attempt at a square-foot garden. It isn't quite finished because I still need to add more grid. I also made a calculation mistake and now my 4x4 isn't square exactly.
I made this bed out of a 2x6x16 that I purchased and had cut at Home Depot. That way, the wood fit in my car easily and I didn't have to get out my hand saw. My 3-foot garden took a 2x6x12.
I just put two big nails in at each corner and the bed was solid. I've seen people use corner angles, and that might be better, but nails are easier.
After I dug up the weeds where my 4x4 was going, I leveled the ground and placed my new garden frame over it. Then, I put down bark to block weeds and provide drainage. Finally, I shovelled in left-over Farmer D compost and started adding the grid.
The grid is very important because without a grid, you don't have a square-foot garden and you cannot make the best use of every inch of soil in the bed. Spacing plants and seeds properly will get you the best bang for the buck.
Finally, I added pine straw all around my beds and in between. I did this for several reasons: first, to deter pests from entering my garden bed from soil level; second, to deter more weeds; third, to keep the mud down around the beds; and finally, to keep moisture in. It was more aesthetically appealing.
A 4 foot square garden can produce enough salad greens for one adult. A three-foot square garden will feed a child. If you want vegetables, too, and some for canning, you would need to add another bed. So, for example, my husband and I want lettuce and vegetables to feed us this summer; therefore, we would need four 4-foot square beds. If we planned on having our granddaughter for the summer, I would plant two three-foot beds for her. I am planning to put cut flowers in my 4x4 and herbs in my 3x3.