Companion Planting refers to the practice of planting two or more different species of plants with the purpose of providing some benefit to one or more of the plant “companions.” The term companion planting can mean different things to different people. The term is generally applied to vegetable gardens, but it can be applied to general landscapes. Some forms of companion planting have been proven effective; others are mostly folk-lore, unsupported by science. Some of the practices that have been labeled as companion planting are shown below.
• Placing plants with similar water needs together is known as hydrozoning and is a recommended practice to produce healthy plants without wasting water.
• Using tall plants to shade shorter plants that don’t need as much sun is known as interplanting and works well in the garden. For example, lettuce can be planted in the shade of tomatoes or broccoli to extend the lettuce season.
• Flowers can be planted between vegetables to attract pollinators and other beneficial insects for crops that need them. It also adds color to the vegetable garden.
• Trap crops, such as radishes, can be used to cut down on insect damage to main crops by providing harmful insects with an alternative food source. A trap crop must be carefully managed so it doesn’t end up increasing the population of unwanted insects. This means spraying the trap crop when the pests gather there. To be effective, trap crops must be planted like a fence, not sprinkled here and there in the garden.
• Strongly scented plants scattered between vegetables can make it harder for pests to find their host plant. Basil, onion, garlic and mint can be used. Note that if you put mint in the garden, keep it in a pot to prevent it from overtaking your entire bed.
• Cover crops can replace nutrients in the soil. A cover crop is planted for the purpose of improving soil quality and nutrition, and/or for attracting beneficial insects. A cover crop, such as cowpeas, vetch, or clover that is planted in the fall and tilled under in the spring is often referred to as a “green manure” crop.
• The “Three Sister” garden is often used as an example of companion planting. Corn is planted first to provide support for pole beans and a few squash or pumpkins are planted in the area to provide shade for the roots. Beans do not provide nitrogen for the corn as it grows; bean plant roots release nitrogen as they break down at the end of the growing season.
The following companion planting practices are not supported by research:
• Placing certain vegetables near each other to improve flavor or vigor of the plant.
• Scattering marigolds throughout the garden to reduce certain root knot nematodes. To be effective, French marigolds should be planted as a solid planting for an entire season. The nematode population will increase again when susceptible crops are planted.
• Carrots “love” tomatoes and beans “dislike” fennel are not supported by science, nor are the companion planting charts found on many internet sites.
Feel free to experiment in your own garden to see what works for you.