What is companion planting?
Companion planting is a gardening practice that places distinct species together that naturally benefit each other in various ways. For example, beans transform nitrogen into a form other plants can use as natural fertilizer. Some plants attract pests, drawing them away from other plants (called "trap cropping"). You could also use taller plants like indeterminate tomatoes to provide afternoon shade to heat-sensitive plants like lettuce. Another example is to grow pollinator-friendly flowers among the vegetables to improve pollination and attract beneficial insects. However, some companion planting literature suggests that one plant "likes" another; those claims generally haven't been backed up by research, but if you can logically correlate what one plant benefits from the other, you are on the right track.
Three Sisters
A traditional and proven companion planting method is "three sisters". The "three sisters" method incorporates dry pole beans, dry corn, and winter squash/pumpkins. All three of these crops are native to the Americas, and this garden combination is most commonly associated with the Iroquois/Haudenosaunee Native Americans, but it is known to have been practiced by many nations, going back to at least the 1300s. Not only is this practice a wonderful way to see nature working in harmony, it can be a valuable teaching tool, introducing children to ideas about nature, history, and food all in the garden—plus, all the seeds are large and easy for kids to work with. It's a true connection to nature and history to know this practice goes many generations back, and that the success of this traditional planting method came from careful observation and experimentation with native plants – no lab coat was needed to prove success.
Here is how the three "sisters" work together: Tall corn stalks provide something on which the pole beans can climb. Climbing pole beans in turn create usable nitrogen, feeding the corn and squash. The squash, which would have traditionally been vining, winter squash (including pumpkins) ramble along the ground, shading the earth with their huge leaves, acting as a water conserving, living mulch that stifles weeds by starving them for sunlight.
How to Sow a Three Sisters Garden
Corn, beans, and squash are all sensitive to frost and transplanting, so they do best if they are sown directly into the garden after your average last frost date. There are lots of variations on this planting style, so don't be afraid to experiment. Amend your soil with organic material as needed and create a mound of soil 4′ across and about 8″ high. Create a wide depression in the mound, that can catch water more easily. Mounded soil warms more quickly in spring, hastening germination, and it also drains better. 1 to 2 weeks after your average last frost date, sow a group of two corn seeds 10"–12" apart and 1" –1 ½" deep in a circle in the center. Two or three weeks later when corn is 4"–6" high, sow bean seeds 6" apart and 1" deep in a circle around each corn stalk. Squash is sown at the same time as the beans. Evenly space three 1" holes for squash seeds about 6" from the edge of the mound placing 2–3 seeds in each hole (more compact squash can be sown more closely for six total plants). Starting the corn first allows it to get going before the beans need to climb and gives corn time to grow before the vigorous squash might shade it and stifle its growth. Remember to thin extra seedlings by clipping just below the soil surface (1" deep for corn) once they have a couple of sets of leaves. Water and watch the three sisters create a happy family!
"Three Sisters" Adaptions
While this traditional "three sisters" works perfectly, there are some adaptions that will also work harmoniously together. First, you can use sweet corn, but just be cautious not to step on a squash at harvest time, because unlike dry corn that is harvested at the end of the season, sweet corn is harvested during the season, while squash is still growing. You can also use tall sunflowers in place of corn, which will not only be quite beautiful but will bring in the bees that are necessary to pollinate the squash. Even though dry beans were traditionally used, you can also grow fresh beans, again being mindful of stepping on squash while harvesting (growing a stand-out variety like purple 'Trionfo' will make finding beans easier, too). If your garden space is limited, grow bush-type squash like a summer squash, or a compact winter squash like an acorn-type so they don't ramble too far, but may just politely overhang your raised bed, also making frequent harvests of fresh beans or sweet corn easier.