Companion planting involves arranging plants in a garden or farm in such a way that they enhance the growth and quality of nearby crops, provide maximum ground cover, and improve the soil. Companion plants can also be employed to help control insect populations. Varieties of plants may be mixed together with or without the use of distinct rows and often add to the beauty of the garden.
Companion planting has a long history, and the techniques used by gardeners have evolved over time from a combination of observation and horticultural science. Some of the principles include:
Trap cropping: the use of a neighboring crop that is more attractive to pests to distract them from the main crop.
Nitrogen fixation: the planting of legumes such as peas, beans, and clover, which have the ability to fix atmospheric nitrogen for their own use and for the benefit of neighboring plants
Pest suppression: some plants exude chemicals that suppress or repel pests and protect neighboring plants
Physical-spatial interactions: tall-growing, sun-loving plants create the ideal space for a neighboring low-growing, shade-tolerant species, resulting in higher total yields
Nurse cropping: tall or dense-canopied plants protect other species that require shade or a windbreak
Beneficial habitats: companion plants attract and support beneficial insects (especially species that are predatory or parasitic to crop-destroying insects), which help control pest populations in neighboring plants
Security through diversity: mixing various crops and varieties provides security to the grower in the event one crop is reduced or lost.
A familiar historical example of companion planting comes from the Native Americans who developed a way to grow a balanced diet on a single plot of land. The “three sisters” they planted together were corn, beans, and squash. Each of these crops is compatible with the others in some way — tall corn stalks support the climbing beans, beans supply their own nitrogen so do not compete with the corn for nutrients, and squash provides a dense ground cover that keeps out weeds which otherwise would compete with the corn and beans.
We employ the principles of companion planting in our test garden at Serosun as a way to demonstrate sustainable gardening practices, to increase the overall productivity of the garden, and to add variety to our harvest.