Did you know that Petunias repel asparagus beetle or that Marigolds planted among potatoes discourage Colorado Potato beetles? Are you aware that cabbage planted near lettuce has an adverse effect on the growth and flavor? In this article I would like to talk about one of my favorite topics, companion planting. Companion planting can be defined as the practice of planting two or more plant species close together to gain benefits either on growth, flavor or pest control. I would like to talk about the many benefits of companion planting in more detail.

  • Trap cropping: when a neighboring crop is selected to attract the pests and distract from the main crop. An example of this is planting collards to attract the diamond back moth from cabbage or planting dill with tomatoes because tomato horn worms prefer dill.
  • Nitrogen fixation: planting legumes such as beans and peas have a relationship with bacteria in the soil called Rhizobium. Legumes can convert it to a form that plants can use.
  • Biochemical Pest Suppression: Some plants can exude chemicals from roots or aerial parts that suppress or repel pest and protect the neighboring plants. An example of this is African Marigold release thiopene which acts as a nematode repellent.
  • Physical Spatial Interactions: Tall growing sun loving plants can share space with lower growing shade tolerate plants. This results in higher yields and has pest control benefits. One of the oldest examples of this is Three Sisters (corn, beans, and squash). Corn is planted for the pole beans to climb and provides a high canopy of foliage that can confuse squash borer and reduce damage. Beans are nitrogen fixing and corn requires a lot of nitrogen. Squash has broad spreading leaves that provide a living mulch and reduce weeds and hold moisture.
  • Beneficial Habitats: provide a desirable environment for beneficial insects such as lady beetles, lacewings, hover flies, mantids, non-insects such as spiders and predatory mites. Plants in the Umbel family (carrots, parsley, dill) are known for this as well as sweet alyssum.
  • Security through Diversity: More mixing of various crops and varieties equals a degree of security to the grower.

Some good examples of Companions are the following:

Broccoli: mint, dill, rosemary; aromatic herbs help repel pest
Cabbage: mint, onion, oregano, dill, sage, clover, chamomile, nasturtium; Chamomile improves the growth and flavor and Nasturtiums offer caterpillars an alternate food source
Carrots: English peas, lettuce, onion family, tomato; maximize space, provide shade and nitrogen fixer
Peppers: tomato, beans, onion, geranium, petunia; Geranium repels Japanese beetles and petunias repel a variety of insects
Spinach: strawberry, cauliflower, eggplant, radish; radish repels leaf miners
Tomato: asparagus, carrot, parsley, basil, marigold, garlic; garlic repels red spider mites

Ashley Stonecipher
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