Guide
How many lettuce and greens per square foot
Leaf lettuce, chard and bok choy take 4 plants to a square, spinach takes 9, and kale, collards and heading lettuce get a square each. How you plan to harvest matters as much as which green it is.
The counts, crop by crop
These come from the same UW-Extension course notes as our square-foot planting chart, taken at a class Mel Bartholomew taught in person. The heading lettuce figure is converted from Clemson's spacing, as explained below.
Heading or leaf lettuce: why the count changes
"How many lettuce plants per square foot" has two answers, because lettuce grows in two shapes. Clemson's lettuce factsheet spaces butterhead and crisphead lettuce 12 inches apart in the row, and 12 inches is one plant per square. Leaf lettuce goes in 6 to 10 inches apart, which converts to anywhere from 1 to 4 per square. The square foot notes use the tight end of that range.
The difference shows up at harvest. Clemson has leaf lettuce ready "as soon as plants are 5 to 6 inches tall," and picking the outer leaves of four plants keeps a square producing for weeks. A head is a single harvest, after which the square sits empty until you replant it.
Baby greens do not follow the count
The numbers above are for plants you mean to grow to full size. Greens cut young are harvested before they touch each other, so they can go in much closer. The course notes use this on purpose: set a large plant such as a cabbage in the middle of a square, then sow "a fast growing crop like radishes, scallions, or even leaf lettuce to harvest when it is young" in the corners while the centre plant is still small.
If you sow thickly and then decide to let the plants grow on, thin them to the listed count. Clemson thins leaf lettuce once the seedlings are 1 to 2 inches tall.
Spinach at 9, kale and collards at 1
Spinach is the dense one, at 9 per square, which works out to 4 inches between plants. Kale and collards sit at the other end with a full square each. Both are cabbage-family plants that get large and are picked leaf by leaf over a long season.
Chard and bok choy fall in the middle at 4. Chard is cut from the outside and keeps regrowing, much like leaf lettuce, while bok choy is usually cut whole.
Keep the squares turning over
Greens grow fast, so one planting rarely fills a square for the whole season. The course notes say to "harvest continually and when a crop in one square is gone, add some new compost and plant a new different crop in that square," and Clemson recommends several lettuce plantings each season for the same reason. Sowing intervals crop by crop are in the days to maturity chart.
Heat is what usually ends a lettuce square. In Clemson's words, "Lettuce does not tolerate hot weather. If this crop is exposed to high temperature or moisture stress, the lettuce will usually have a bitter flavor and will also bolt." Slow-bolting varieties help. In summer, a spot that misses the afternoon sun helps too, and the sunlight requirements chart gives each crop's light band.
Frequently asked
Four for leaf lettuce and one for heading types such as butterhead and crisphead. Clemson's factsheet spaces heading lettuce 12 inches apart, which is one plant per square foot, and leaf lettuce 6 to 10 inches apart.
Nine, which corresponds to 4-inch spacing. The figure comes from UW-Extension course notes taken at a square foot gardening class taught by Mel Bartholomew.
One. Kale and collards grow large and are picked leaf by leaf, so the square foot gardening notes give each plant a full square.