Raised Bed Planting Density Calculator

Square foot gardening (SFG), popularised by Mel Bartholomew, divides the bed into 1-foot squares and plants one type of crop per square at a density based on the plant's mature width. Large plants like broccoli and tomatoes get one plant per square foot. Medium plants like lettuce get four per square. Small plants like radishes get sixteen per square. This system maximises yield while minimising weeding.

Most vegetables need at least 6 to 8 inches of root depth. Shallow-rooted crops like lettuce, radishes, and herbs grow well in 6-inch beds. Deep-rooted vegetables like tomatoes, carrots, and parsnips need 12 to 18 inches. The USDA recommends 12 inches as a general-purpose depth. Fill with a high-quality mix: compost, topsoil, and coarse material for drainage.

1 plant per square foot: broccoli, cabbage, pepper, tomato, eggplant. 4 per square: lettuce (large), chard, parsley. 9 per square: spinach, beets, beans, turnips. 16 per square: radishes, carrots, onions, garlic. These spacings are adapted from USDA Cooperative Extension square foot gardening guides.

Soil volume (cubic feet) = Length x Width x Depth (all in feet). A 4x8 foot bed, 12 inches (1 foot) deep requires 4 x 8 x 1 = 32 cubic feet of soil mix. Bags of potting mix are typically 1 to 2 cubic feet. A cubic yard of bulk mix (27 cubic feet) fills a standard 4x8-foot bed to 12 inches depth.

USDA and extension research suggest 100 to 200 square feet of growing space per person for year-round vegetable production in most US climates. Three to four 4x8 beds (96 to 128 sq ft) can supply significant vegetables for a 2-person household through the growing season. Add cold frames or row covers to extend the season and increase yield.