The Square Foot Gardening method was developed by Mel Bartholomew and first described in a 1981 book by that name. The method uses densely planted raised beds and specific soil mixtures. Garden space is divided into beds that are easily accessed from every side - typically 4 feet by 4 feet - and are 6 inches deep. For vegetables such as carrots and asparagus that require more root space, 12 inches of soil are recommended. Each bed is divided into approximately one foot square units and marked out with sticks, twine, or slats. Different seeds are planted in each square. Common spacing is one plant per square for larger plants (broccoli, basil, tomato, etc.), four plants per square for medium large plants like lettuce, nine plants per square for medium-small plants like spinach, and sixteen per square for small plants such as green onions and carrots. Plants that normally take a lot of space such as squash or cucumbers, are grown vertically on trellises.
The recommended soil mixture is one-third compost, one-third peat moss, and one-third vermiculite. The compost should be a mixture of multiple different forms such as worm castings, green waste, or manure. A few handfuls of compost are added to each square with each harvest to maintain fertility. The beds are weeded and watered from the pathways, so the garden soil isn't stepped on or compacted.
This gardening method has been used successfully in every region, including in deserts, on high arid mountain plateaus, in cramped urban locations, and in areas with polluted or high salinity soils.