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Companion Planting

July 2, 2010

Companion planting is an important strategy of organic gardening.  The use of companion plants is essentially encouraging a polyculture in your garden, growing different types of crops together.  This plant diversity in the garden provides some security for the home gardener.  Growing a variety of crops as well as various cultivars means that the gardener will always have a harvest.  If one crop is blighted with disease or insect damage, other crops will continue to grow and thrive. 

Companion planting builds on this idea of diversity by planting different vegetables, flowers and herbs in close proximity to one another based on their shared benefits.  In this way, the plants are helping each other grow while making the most efficient use of space.  There are five main ways in which plants may help each other.  These are described below.       

Physical spatial companions

These are companions that are planted near each other based on their growth characteristics and needs.  For example, tall plants can provide shade to low growing plants which act as living mulch, reducing weeds and shading the soil.

  • Plant tall growing, sun-loving plants with low growing, shade-tolerant species
    • Corn with squash
    • Pole beans on a trellis or tall flowers with lettuce
    • Corn with peas
    • Tomatoes with leafy greens
  • Plant deep root plants with shallow root plants
    • Cucumber and spinach
    • Parsnip and onion

Nitrogen fixers

This strategy takes advantage of the ability of peas and beans to convert atmospheric nitrogen into a form that is usable to plants.  This reduces the need for any organic or synthetic nitrogen amendments. 

  • Plant members of the Fabaceae family, pea, beans and clover, near plants with high nutrient needs.
    • Peas or beans with corn
    • Peas grow well with most vegetables excluding the Onion Family and potatoes.
    • Beans grow well with most vegetables excluding the Onion Family, sunflowers and fennel.  Pole beans are best planted with tall growing vegetables such as corn or grown on a trellis near companion vegetables.  

Onion Family members grow well with leafy greens.

Pest repellents

Some plants secrete compounds that repel specific pests that live in and around the soil while others let off pungent scents through their leaves and flowers.  These scents can confuse pests and often repel specific insects.   

  • Nasturtiums, false indigo, elderberry, marigolds, Artemisia, yarrow and basil all have this affect in gardens.
  • Liliaceae, the Onion Family, give off scents which confuse insects.
  • Mints seem to repel insects.
  • Low growing thyme or lavender may deter slugs.
  • Tansy and pennyroyal repel ants.
  • Thyme and chamomile may repel cabbage moths.
  • Potatoes and beans confuse each other’s insect pests.

 

Beneficial habitats

This form of companion planting involves the use of flowers and other plants to attract beneficial insects.  These plants provide a desirable environment for beneficial insects and arthropods.  Beneficial insects include pollinators, predators and parasites.  Pollinators are important for fruit and seed set while predators and parasites feast on pest insects.     

  • Apiaceae, the Carrot Family, are good insectary plants.  They attract predatory wasps and flies.
  • Asteraceae, the Sunflower Family, including daisy, coneflower, black-eyed Susan, and sunflowers attract beneficial insects.
 

This nasturtium leaf covered in aphids can be removed from the garden.

Trap crops

Trap crops are plants whose scents attract insects, luring them away from other crops.  Insects will feed on and lay their eggs on trap crops.  These crops can then be destroyed before eggs hatch. 

  • Radishes draw flea beetles away from other plants, especially other members of the Cabbage Family.
  • Collards can attract the diamond back moth away from cabbage.
  • Nasturtiums and mustard contain mustard oil which attracts pests.  Nasturtiums can be used as a trap crop for aphids.

 

Please note:  Much information about companion planting comes from gardening folklore; few companion planting interactions have actually been researched.  Try these suggestions in your garden and see how they work for you!

Top Ten Companion Plants

A table of companion plants

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