Companion Planting is based on the idea that certain plants can benefit others when planted next to, or close to one another.1 The process assists other plants via nutrient uptake, pest control, pollination, and other factors necessary to increasing crop productivity.1


History

In China the mosquito fern has been used for at least one thousand years, as a companion plant for rice crops. It hosts a special cyanobacterium that fixes nitrogen from the atmosphere, and blocks out light from getting to any competing plants.2
Companion planting was practiced in various forms by the indigenous peoples of the Americas prior to the arrival of Europeans. One common system was the planting of corn (maize) and pole beans together.2 The cornstalk would serve as a trellis for the beans to climb, while the beans would fix nitrogen which also benefited the corn. The inclusion of squash with these two plants completes the Three Sisters technique, pioneered by Native American peoples.2
Companion planting was widely touted in the 1970s as part of the organic gardening movement. It is also a technique frequently used in permaculture, together with mulching, polyculture, and changing of crops.2

Examples of Companion Plants
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Fig. 1: Here is an example of Marigolds being planted with Kale, acting as a natrual pesticide.

There are hundreds of companion planting combinations to be tested in the garden.
Below are a few examples or organic crops that will show amazing results! 3
Plant
Companion(s) and Effects
Asparagus
Tomatoes, parsley, basil
Basil
Tomatoes (improves growth & flavor); said to dislike rue; repels flies & mosquitoes
Cabbage Family (broccoli, brussels sprouts, cabbage, cauliflower, kale, kohlrabi)
Potatoes, celery, dill, chamomile, sage, thyme, mint, pennyroyal, rosemary, lavender, beets, onions; aromatic plants deter cabbage worms
Garlic
Roses & raspberries (deters Japanese beetle); with herbs to enhance their production of essential oils; plant liberally throughout garden to deter pests
Marigold
The workhorse of pest deterrents; keeps soil free of nematodes; discourages many insects; plant freely throughout the garden.
Tomato
Chives, onion, parsley, asparagus, marigold, nasturtium, carrot, limas


Categories

Companion plants can benefit each other in a number of different ways, including:
  • Increased Level Interaction — Plants growing at different heights in one space, providing ground cover or working as a trellis for another plant. 3
  • Nitrogen Fixation — Plants that fix nitrogen in the ground, making it available to other plants.3
  • Pest Suppression — Repelling pest insects, weeds, nematodes, or pathogenic fungi, through chemical means.3
  • Pollinator and Predator Recruitment — Plants that produce nectar and protein-rich pollen in a vegetable garden recruit higher populations of beneficial insects that control pests.3
  • Positive Hosting — Plants attract/carry beneficial insects or other organisms which help plants, as with ladybugs or some "good nematodes".3
  • Protective Shelter — One type of plant protecting others from wind or sun.3
  • Trap Cropping — Plants that attract pests away from others. 3

How-To Tutorials

Watch a video on companion planting the sustainers of life, also known as the
Three Sisters Technique: beans, corn, and squash, following how to plant them in a raised bed!

Techniques

Companion Planting combines Mother Nature's techniques as well as your own chosen crops. A few techniques to ease the process include:
  • Mix up monocrops. If you want to grow a lot of one crop, plant several small plots in various areas of your garden and mix the crop with one other vegetable or flower. 3
  • Interplant herbs and flowers. By interplanting the two, you can attract beneficial insects and birds, which are natural predators to many pests. Flowers and herbs can also confuse pests and deter them from finding your prize crop.3
  • Provide refuge for beneficials. Create habitats in your garden for creatures that prey on those pesky ones. Such beneficials include toads, lizards, snakes, birds and various insects. These organisms need food, water, shelter and breeding grounds in order to find a happy home in your garden. Groundcovers, hedgerows, rock piles, and perennial plants provide needed shelter. Birdbaths and bird feeders also encourage necessary critters.3
  • Use organic pesticides as the last resort. Many of the OMRI approved chemicals may be safer; however, they still have some toxic residues that can harm the natural balance in your garden. They work very well at killing the pests, but they can also harm helpful insects like butterflies and bees.3
  • Know your weeds. Identify the weeds and wildflowers that pop up in your garden space and learn which ones attract native beneficial organisms.3

Interesting Facts
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Fig. 2: A diagram of a small-crop garden illustrated using the precepts of companion planting.

Did you know..
- Companion Planting is used by famers and gardeners in both industrialized and developing countries for many reasons (i.e. availability, affordability, success rates, etc.)4
- That often the companionships are one-sided (i.e. Whle carrots benefit beans, beans do not offer the same effect)3
- There is no scientific method of determining which plants will benefit others-- it is simply the word of a seasoned gardener4
- Bay leafs are an ideal way to rid your house of ladybug invasions4
- Plants are often compared to humans in the sense that they need "companions" to survive1

Quick Quiz

Questions:
  1. Give an example of three ways which plants can benefit their companions.
  2. Native Americans created the Three Sisters technique which involves which vegetables?
  3. Marigolds are commonly recognized for eliminating what from the garden?
  4. What is the definition of "Increased Level Interaction"?
  5. Why is it important to interplant herbs and flowers?

Answers
  1. Nutrient uptake, pest control and pollination.
  2. The Three Sisters technique includes beans, corn and squash.
  3. Marigolds eliminate many insects.
  4. "Increased Level Interaction" refers to plants growing at different heights in one space, providing ground cover or working as a trellis for another plant.
  5. It is important to interplants herbs and flowers as you can attract beneficial insects and birds, which are natural predators to many pests. Also, flowers and herbs can confuse pests and deter them from finding your prize crop.

Glossary


Cyanobacterium: A photosynthetic bacteria that fixes nitrogen, also known as blue-green algae.
Crop Productivity: Agricultural productivity measured as the ratio of agricultural outputs to agricultural inputs.
"Fixing Nitrogen": The process of chemically altering unusable, free atmospheric nitrogen into a form usable by organisms.
Interplant: Plant (a crop or plant) together with another crop or plant.
Monocrops: A cultivated crop that does not rotate with other crops in a particular field or area
Mulching: To apply/treat or cover with a mulch.
Nematodes: A form of nematode,which is a worm of the large phylum Nematoda, such as a roundworm or threadworm.
Nutrient Uptake: The absorption of microorganisms.
OMRI: Organice Materials Review Institute.
Permaculture: The development of agricultural ecosystems intended to be sustainable and self-sufficient.
Pollination: The process by which pollen is transferred in the reproduction of plants, thereby enabling fertilization and sexual reproduction.
Polyculture: Agriculture using multiple crops in the same space, in imitation of the diversity of natural ecosystems, and avoiding large stands of single crops, or monoculture.


References

1. Dancer V. Companion Planting - Secrets of Organic Gardening [Internet]. 2006 [cited 2012 Jun 17]. Available from: http://www.companionplanting.net/.
2. Pest control | Companion planting [Internet]. [updated 2010 Oct 27; cited 2012 Jun 17]. Available from: http://blog.notcutts.co.uk/latest-articles/2010/10/27/pest-control-companion-planting.html.
3. Carter K. Seeds Of Change [Internet]. [updated 2006 Apr; cited 2012 Jun 17]. Available from: http://www.seedsofchange.com/enewsletter.
4. Companion Planting [Internet]. [updated 2012 May 27; cited 2012 Jun 17]. Available from: http://www.ghorganics.com/page2.html.