What is Companion Planting?
Biointensive farming expert, John Jeavons, defines companion planting as “the placing together of plants having complementary physical demands.” He broadens the definition even further, saying it is “the growing together of all those elements and beings that encourage life and growth: the creation of a microcosm that includes vegetables, fruits, trees, bushes, wheat, flowers, weeds, birds, soil, microorganisms, water, nutrients, insects, toads, spiders, and chickens.”
In this article, we’ll go over the benefits of companion planting that Jeavons grouped into the following categories:
- Physical Complementarity
- Weed Control
- Insect Management
While enhanced health and growth have been documented in many crops when planted as companions, much of the scientific explanation for the “why” remains unknown. Many of the symbiotic relationships have been merely observed by the first-hand experience of farmers and researchers.
For example, green beans and strawberries thrive when grown next to one another, as do butter lettuce, and spinach. However, onions are known to inhibit the growth of peas and beans. Beets seem to be indifferent to bush beans, but definitely do NOT like pole beans. Why exactly all of these plants respond in these ways is yet to be determined, but nevertheless, it has been observed and documented.
When it comes to health, recommended biointensive spacing is also important to factor in. Even beneficial companions when planted too close to one another can fail to thrive. It’s kind of like living a little too close to your in-laws. We all need the right amount of space 😉 The goal is for the leaves of neighboring plants to just barely be touching when they’ve reached maturity, forming a canopy that covers the soil.
Many herbs have been shown to benefit the entire plant community. Whether it’s stimulating a healthy population of microorganisms in the soil, attracting beneficial insects and pollinators, combatting disease, or mining minerals with their deep root systems, they all have wonderful things to offer.
For this reason having beds of herbs growing among your vegetable crops, in hedgerows, or on the perimeters of your market garden is always a good idea. Beneficial herbs include varieties such as:
- Lemon Balm
- Stinging Nettle
Nutrient Companions In Time
Jeavons likens the practice of crop rotation to “companion planting over time.” As mentioned in my previous article on crop rotation, he identifies three groups of crops when it comes to nutrient cycling:
- Heavy Feeders
- Heavy Givers
- Light Feeders
As their name suggests, Heavy Feeders are crops that consume large quantities of available nutrients in the soil, especially nitrogen. When rotating crops on an annual basis, the plots that these crops occupied would then be planted with Heavy Givers, plants that harness nitrogen from the atmosphere and channel it to nodules in their root systems. When these root systems are broken down by microorganisms in the soil, the nitrogen is then converted into a usable form for the plants.
Following Heavy Givers, Light Feeders (typically root crops) will be the next category of plants to be planted in a rotation plan. These crops consume a minimal amount of nutrients, leaving plenty of food behind for the Heavy Feeders which will follow next, repeating the cycle.
Nutrient Companions In Space
Not only can Heavy Feeders, Heavy Givers, and Light Feeders work together as companions over time, but they can also be planted in proximity to each other in space. This can take the form of interplanting two to three crops within the same bed at the same time, such as corn, bush beans, and beets.
There are different approaches to interplanting, and it all depends on the needs of the crops you are working with, as well as your context when deciding which to experiment with.
- Completely intermingle your companion plantings throughout the entire bed.
- Alternate rows of different companion crops within the same bed
- Divide a bed into multiple sections for the different companion crops (essentially creating “mini-beds” within a bed).
Methods one and three would likely be more feasible in a home garden, while method two would most likely be used in the market garden context, where having a single row of a specific crop would be more efficiently planted and harvested for profit, such as planting basil along the edges of your tomato beds.
Full Sun/Partial Sun
Most are familiar with the fact that some plants thrive in full sun, while others only like partial sun, with many others falling at different places within the spectrum. Learning these preferences, and finding symbiotic relationships where companion plants are helping one another is the goal. For example, lettuce and carrots (which can thrive in partial sun) can often be comfortably tucked in with taller growing, trellised sun-loving plants. Crops like swiss chard and spinach will thrive in the shadows behind tall growing corn.
Shallow Roots/Deep Roots
A good example of a deep-rooted crop benefitting from proximity to a shallow-rooted crop would be beans with corn. Their root systems occupy different levels in the soil and will not compete with each other. The bean’s roots are shallower, while the roots of the corn go deeper. The beans will also be fine in the dappled shade of the corn plants
One of the best examples of strategic companion planting combining both fast and slow-maturing plants is from the French intensive farmers of the late 1800s. From about 1850 to 1910, ⅙ of the city of Paris was composed of market gardens. There are records of farmers broadcasting radishes and carrots into the same bed as companion crops. The radishes would germinate first and begin to grow, being a very fast-growing crop. As the radishes were harvested, head lettuce would be transplanted into the same bed at one-foot spacing. The lettuce would be ready for harvest just as the carrots were starting to need more space for maturity. When the lettuce came out, cauliflower transplants were put in. Finally, the carrots were harvested, and the cauliflower would finish out the cycle having the bed all to themselves.
Many crops are significantly slowed down in their ability to mature in health due to competition from native weeds. One strategy to mitigate this is by interplanting crops that naturally form a canopy to smother weeds, like squash. This can be done in a crop rotation approach, where a crop sensitive to weeds is planted after a weed-smothering crop in a rotation plan. Or it can happen simultaneously with interplanting. The Three Sisters Guild is a good example of this.
The Three Sisters Guild
The Three Sisters Guild is a Native American strategy, using the symbiotic triad of corn, pole beans, and squash. When these three crops are grown together, they can maximize yields in a given space with each crop contributing to the mutually beneficial relationship.
When planting this triad, begin with the corn. Once the corn stalks are about six inches tall, pole beans can be planted around the base of the stalks, and simultaneously the squash can be planted to fill out the remaining bed space. As these crops grow, multiple functions take place:
- The broad leaves of the rambling squash form a natural ground cover that cools the soil, preserves moisture, and shades out the weeds.
- The beans provide nitrogen for themselves, the corn, and the squash.
- The corn provides a trellis for the vining beans to climb.
- Unique sugars from the roots of the corn feed bacteria that convert the nitrogen nodules on the roots of the beans into a usable form for all three plants.
When planting herbs or flowers that repel pest insects, Jeavons stresses two main factors to keep in mind:
- Plant the repelling herbs or flowers well in advance of the crops they will eventually be protecting. The aromas and essential oils need to be matured and present so the insect pest already understands that space to be an “unpleasant” place to propagate.
- Plant a variety of herbs and flowers, at least five. Having multiple species has been shown to greatly enhance this strategy’s effectiveness.
Here is a list of some varieties known to help repel certain insects:
- Marigold – repels white flies
- Spearmint, Tansy, and Pennyroyal – repels ants
- Mexican Marigolds – repels nematodes and root pests
- Garlic, Stinging Nettle, Spearmint – repels aphids
- Borage – repels tomato hornworm
Taking the time to plant herbs and flowers as peripheral companion crops to attract beneficial pollinators is always worth the effort. Bees are attracted by many herbs and flowers such as
- Lemon Balm
- Pot Marjoram
- Sweet Basil
- Summer Savory
A beneficial plant I’ve personally experienced very good results from is Buckwheat. When sown next to your tomatoes, it can greatly reduce aphid pressure. The beautiful white blossoms of the buckwheat attract parasitic wasps: tiny harmless little flies. Harmless to humans, that is. They lay their eggs INSIDE of the aphids as their host, killing them in the process. This greatly knocks down aphid populations before they have a chance to get established and become a problem.
Discoveries of companion planting relationships are continually evolving. There are many charts published online to refer to when determining which crops are beneficial companions, and which are antagonists.
While it’s a fascinating field of study, it can also be overwhelming to try and incorporate it into your crop system when growing food for profit. The home garden is a much lower-risk context to experiment with intercropping and new potential benefits of different crop pairings.
Hopefully, this article has provided you with some good food for thought, and perhaps new ideas for how to utilize the strengths and weaknesses of different crops in order to benefit each other. If you have successfully incorporated intercropping different crops in the same bed in a profitable market garden context, I’d love to hear about your experiences! Sharing this information as a resource to help other farmers is what we’re all about!
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This topic interests me, but there are some major issues with intercropping at scale. One, the market gardens of Paris used tons and tons of horse Manure; super expensive, and then there is the fallout with area organizations about runoff (take what Singing Frogs Farm in CA has had to go through…). Another problem is harvesting. So challenging and much slower to harvest through and between other crops. Let’s not forget about zones! Where we are in Maine, it’s a very short growing season. Having mature plantings of herbs prior to transplants going in at the beginning of the season just ain’t happen’. Perhaps the biggest issue is air flow. One could be inviting botrytis, fusarium wilt, powdery mildew, and a whole host of diseases if crops aren’t able to get the maximum amount of airflow due to proximity to other plants. So, so many things to consider, and most businesses would never have the resources to experiment with these options at scale. Still an extremely valuable approach, but on our farm, we focus on growing these crops nearby one another in separate beds or along hedgerows. At least they’re in the same growing area. I hope to learn more about intercropping for the future of our farm. There are some terrific ways to grow, and no one farm can do it all. Thanks for writing this article!
Absolutely a fascinating topic, however, the anecdotal ‘evidence’ available seems to far outweigh the availability of actual science on the topic. My favorite so far is that mint repels cabbage moths – which I observed landing on said mint or seeking refuge in it when I chase them like a crazy man.
On the other side, I fully concur about buckwheat. We have seen the parasitic wasp activity rise drastically with buckwheat present.