Square Foot Garden Planner
Square foot gardening divides a raised bed into a grid of 1-foot squares and plants each square with a set number of plants based on their spacing – one tomato, four lettuces, nine bush beans or sixteen carrots. It is an intensive, tidy way to grow a lot of food in a small space. This planner counts the squares in your bed, converts any seed-packet spacing into plants per square, and works out how much of the classic one-third blend of compost, coir or peat, and vermiculite you need to fill it.
How to use this calculator
- Choose imperial (1 ft squares) or metric (30 cm squares).
- Enter the inside length, width and soil depth of your bed. A classic square foot garden is 4 × 4 ft and 6 inches deep.
- Type the plant spacing printed on the seed packet. The planner shows how many plants fit in each square.
- Use the soil table to buy equal volumes of compost, coir or peat moss, and vermiculite.
- Sketch your grid on paper and assign a crop to each square, using the plants-per-square chart below.
How plants per square is calculated
A square is 12 inches across. Dividing 12 by the seed-packet spacing and rounding down gives the number of plants along each side; squaring that gives the plants per square. For a spacing of 12 in that is 1 plant, 6 in gives 2 × 2 = 4, 4 in gives 3 × 3 = 9, and 3 in gives 4 × 4 = 16. Crops that need more than 12 inches – such as squash or sprawling tomatoes – take one plant per square or span several squares. In metric, the same logic applies to a 30 cm square.
Plants per square at a glance
| Per square | Typical crops |
|---|---|
| 1 | Tomato (staked), pepper, eggplant, broccoli, cabbage, cauliflower, kale |
| 2 | Cucumber or pole peas on a trellis (along one edge) |
| 4 | Lettuce, chard, marigolds, basil, parsley, strawberries |
| 9 | Bush beans, beets, spinach, turnips |
| 16 | Carrots, radishes, onions, garlic (small) |
The soil mix
The method’s founder recommended filling beds with equal parts by volume of blended compost, peat moss and coarse vermiculite. Many gardeners now swap peat for coconut coir. The planner calculates the bed volume as length × width × depth and divides it by three. A 4 × 4 ft bed 6 inches deep holds 8 cubic feet, so you need about 2.7 cubic feet of each component. Using compost from several different sources gives a wider range of nutrients. Mix everything thoroughly and moisten it before planting.
Worked example
A 4 × 8 ft bed has 32 squares. If you give 4 squares to tomatoes (4 plants), 4 to peppers (4), 6 to lettuce (24), 6 to carrots (96), 4 to bush beans (36), 4 to beets (36) and 4 to herbs and flowers, you use the whole bed. At 6 inches deep it holds 16 cubic feet of mix – about 5.3 cubic feet each of compost, coir and vermiculite.
Tips for success
Keep beds no wider than 4 ft so you can reach the middle without stepping on the soil. Mark the grid with thin wooden lath or string so the squares stay visible. Put tall and trellised crops on the north side (in the Northern Hemisphere) so they do not shade shorter plants. When you harvest a square, add a trowel of compost and replant it straight away with another crop – this succession planting is where square foot gardening really pays off.
Frequently asked questions
How many plants per square foot?
Divide 12 by the seed-packet spacing in inches, round down, and square the result: 12 in spacing gives 1 plant, 6 in gives 4, 4 in gives 9 and 3 in gives 16 plants per square foot.
How deep should a square foot garden be?
The original method uses 6 inches (15 cm) of mix, which suits most vegetables. Deep-rooted crops such as carrots and potatoes do better with 12 inches, either in a deeper bed or a deeper section.
How much soil for a 4×4 square foot garden?
At 6 inches deep a 4 × 4 ft bed holds 8 cubic feet – about 2.7 cubic feet each of compost, peat or coir, and vermiculite.
Can I use regular garden soil instead of the mix?
Yes, a good loam amended with plenty of compost works well, especially in deeper beds. The light one-third mix holds water and drains well, which is why it is popular for shallow beds.
How many tomato plants fit in a square foot garden?
One staked or caged indeterminate tomato per square. Bushy determinate varieties may need two to four squares each.