Nancy Garrison, Urban Horticulture Advisor and Master Gardener Program Coordinator
February, 2002

Introduction

Companion planting is the concept of placing plants together that have complementary needs. These needs relate to the health, nutrition, use of physical space of the plants as well as interactions with weeds, insects, and other organisms. The interrelationships between plants and their environment are very complex. Our knowledge based on scientific research about companion planting is not sufficient for me to begin to speak with authority on the subject. Instead, I will primarily explain the different angles to consider.

Strategies

Companion planting for better plant growth
This seems to be the angle that is most often thought of when one speaks of companion planting. It is a premise based on the observation that some plants do better when planted in close proximity, some do worse, and some combinations appear to have a neutral effect on each other. This information comes from a list that has been circulating for the last 30 years that originated from Rodale's Feb. 1972 Organic Gardening and Farming magazine – "A List of Common Garden Vegetables, Their Companions and Their Antagonists".
Some beneficials are noted for having positive effects on other plants for reasons such as:

• Attracting bees (African Blue Basil)
• Increasing oil content in certain herbs (stinging nettle)
• Concentrating certain nutrients in its body (stinging nettle)
• Encouraging health and disease resistance (Valerian)
• Soil life stimulation (stinging nettles)
• Soil regeneration (sow thistle, rye plant)

For nutrition "over time"
Crop rotation
Complementary nutritional needs
Pole beans (heavy givers) and corn (heavy feeders) planted together or crop rotation is a form of this.
Mutual Support

• Sun/shade – plant lettuce in the partial shade provided at the edge of a corn planting.
• Fast and slow maturing – radishes and broccoli
• Vertical location of plant's edible part – Corn and winter squash

Insect/"pest" control
This capitalizes on well developed aroma and essential oil accumulations and may involve repellency, trap cropping, antagonist root exudation, beneficial root exudation or attracting beneficial parasites, predators or birds that feed on what we call "pests". Some examples:

• Ants – Spearmint, tansy, pennyroyal
• Nematodes – Mexican and French marigold
• Aphids – yellow nasturtiums
• Tomato worm – borage

I think the most important strategy we can employ is to:

• Incorporate a broad spectrum of herbs that are allowed to flower.
• Plant flowers that attract beneficials by providing pollen and nectar (alternate food source).
• Eliminate any use of broad spectrum toxic pesticides.
• Become an observant participant in your garden learning to read its story and responding with compassion and good stewardship.
• Realize there is an underlying order and harmony in all beings of creation.