Companion planting means "growing two or more plant species in close proximity so that some cultural benefit is obtained," according to the Ohio State Cooperative Extension. The benefits of companion planning include insect control, better yield, or improved flavor. Follow traditional companion planting groupings--like the Native American interplanting of corn, squash, and beans--and carefully observe the results in your own garden to develop the best companion plantings for your location.
Three Sisters Experiment
Native Americans across North America grew the Three Sisters of corn, beans and squash in beautifully designed round and oval garden plots. According to the National Sustainable Agriculture Information Service, interplanting these three native North American crops produces high yields with minimal negative impact on the soil and environment, which allowed indigenous peoples and early European colonists to thrive here. Planting a Three Sisters garden plot and comparing it to separate single-crop plantings of corn, beans and squash is a great way to experiment and learn about companion planting.
Choose heirloom varieties of corn with tall, strong stalks, native climbing beans like Scarlet Runner or Rattlesnake, and a type of winter squash well adapted to your area. Interplant one bed with the three plants, and plant three small separate beds, one of each type. Carefully record the growing results including measurements of plant growth and date and weights of produce to determine if the companion planting improved yields.
Companion planting can act as a natural pesticide in one of two ways: Either one plant chemically repels bugs which would otherwise flock to eat its neighbor, or one plant serves as a sacrifice plant, attracting bugs to eat it instead of its more valuable neighboring crop. According to the North Dakota Cass County Cooperative Extension, sage will deter carrot flies from carrots, nasturtium and rosemary will keep beetles off of beans, and chives will keep aphids off of celery. Trap-cropping, or planting a sacrifice plant to keep bugs off another plant, include using collards or Chinese mustard to keep diamond-back moths or flea beetles from eating cabbage.
Shade and Sun
Physical-spacial interactions are a natural companion planting trick: Short plants that thrive in the shade can be interplanted with taller plants which need full sun. According to the National Sustainable Agriculture Information Service, physical-spacial interplanting can increase yields from the same amount of space. For example, lettuce can be grown between tomato rows or under asparagus plants once they've leafed out. The lettuce will remain cooler in the taller plant's shade, helping it to thrive, while shallow-rooted lettuce will help keep out weeds which could steal the taller plant's water and nutrients.
Cool weather crops like brussels sprouts can also be planted in the shade between rows of heat-loving plants like peppers and eggplants; when night temperatures drop below 40 degrees and peppers and eggplant production comes to a halt, remove the plants and the brussels sprouts will leap to production in the full sun of cooler autumn days.