Companion planting is an ancient agricultural practice that is based on growing different plant species near to one another to provide mutual benefits. In a nutshell, the primary goals of companion planting at home include increasing crop yields, controlling pests and diseases, and improving soil fertility.
By PENNY SWIFT
While there is anecdotal evidence and historical practices that support companion planting, the scientific research on its efficacy is a bit limited. Some plant combinations may have beneficial effects, while others may not live up to their reputation. Ultimately, do we need science or personal experience to prove whether companion planting works or not?
Does Companion Planting at Home Work?
There is absolutely no doubt that some plants grow much better when you plant them next to, or even amongst other plants. Like people, good companions have the ability to shelter one another and give support in various ways. These include sharing nutrients, chasing away bad bugs, and attracting insects that will pollinate their companions.
Even though companion planting is recognized to be one of the least understood ecological subjects, it also appears that companion plants (again like people) are often opposites. So, some plants that love the sun will provide shelter for those that don’t. Some plants with shallow roots are happy to share their environment with those that have deep-growing roots.
Similarly, some slow-growing plants do well with those that grow slowly, because their needs vary at different times. For instance, a plant that flowers early will produce pollen and nectar that might attract insects that benefit the second plant. Heavy feeders often do well with light feeders or those that need different nutrients. They often stimulate biological activity in the soil that benefits the heavy feeders.
By paying attention to the plants that do well together, as well as those that don’t like one another, you will find that you are able to grow a much wider variety of plants in your backyard. You will also find that it is a lot easier to control pests and produce disease-free crops.
In essence, companion planting is a method of planting and growing various plant species together for mutual benefit. Ultimately, if you choose the right companions, this type of planting will help you to produce a healthy, organic, and really “green” garden that will be sure to flourish.
Common Companion Planting Principles and Their Benefits
Here are a few companion planting principles and basic benefits to inspire you.
Some plant combinations repel pests or attract beneficial insects that prey on harmful ones. For example, marigolds are often planted alongside vegetables to deter pests like aphids and nematodes. At the same time, they will attract ladybugs that eat many harmful insects. Also, planting onions with carrots can deter carrot fly, and carrots can help deter onion fly, benefiting both crops. And growing aromatic herbs like thyme, rosemary, and sage near cabbage, broccoli, and cauliflower can help repel pests like cabbage moths.
Certain plants have natural properties that can help suppress diseases in nearby plants. For instance, growing basil near tomatoes is believed to reduce the incidence of tomato diseases like blight.
Some plants can improve soil fertility by fixing nitrogen or adding organic matter. Legumes, such as beans and peas, are known for their ability to fix atmospheric nitrogen into the soil, benefiting neighboring plants that require nitrogen.
Companion planting at home can make efficient use of space by combining plants with different growth habits. For example, tall plants like corn can provide support for climbing plants like beans. A good example explains why carrots love tomatoes. Carrots have a relatively shallow root system, while tomatoes have a deeper one. By planting them together, you can make efficient use of the soil depth, allowing both crops to thrive without competing for root space.
Planting certain species together can help smother weeds and reduce weed competition for crops. For example, the “three sisters” is a classic Native American planting method where corn, beans, and squash are grown together. Corn provides a trellis for beans to climb, beans fix nitrogen for the other two, and squash spreads along the ground, suppressing weeds.
A Scientific Approach to Companion Gardening
Despite its limitations, there is some scientific and quasi-scientific research that is informative. Generally, companion planting is considered to be a small-scale gardening practice – which is why companion planting at home makes such a lot of sense. It’s a practice that you and I can use in our gardens, not one that commercial growers are likely to embrace.
According to ATTRA (Appropriate Technology Transfer for Rural Areas), a national U.S. center for sustainable agriculture information, the concept embraces different strategies that increase the biodiversity of agroecosystems. They also explain that contemporary companion gardening has evolved from a combination of historical observation, horticultural science, and a few unconventional sources.
In a technical horticultural paper, Companion Planting: Basic Concepts & Resources, George Kuepper and Mardi Dodson outline the scientific foundations for companion gardening. They are trap cropping, symbiotic nitrogen fixation, biochemical pest suppression, physical spatial interactions, nurse cropping, beneficial habitats, and security through diversity.
This is when a companion plant is selected to attract pests that a neighboring crop. For example, collards (a type of Brassica that is related to cabbage, broccoli, and Brussels sprouts), are planted alongside cabbages to attract the diamondback moth away from the cabbage crop.
Symbiotic Nitrogen Fixation
This approach involves planting legumes (including peas, beans, and clover) that absorb nitrogen from the atmosphere for their own use, and then transfer nitrogen into the soil. Similarly, forage legumes are often seeded with grasses to reduce the need for nitrogen fertilizer. Also, beans are sometimes planted with corn.
Biochemical Pest Suppression
When chemicals seep out of the roots or stems of certain plants they can repel or suppress pests that would normally attack nearby plants, including tomatoes, sugar beets, and soybeans. The best-known example is the marigold (Tagetes spp), which releases thiophene, a proven nematode repellent, into the soil.
Physical Spatial Interactions
Many tall-growing plants that thrive in the sun grow happily with plants that prefer to be in the shade. A good example is corn grown with low-growing squash or pumpkin.
Here, tall plants with thick foliage protect more vulnerable species by shading them or shielding them from the wind. Although similar in concept to physical spatial interaction, nurse cropping is often used to protect certain crops. So, for instance, oats will be sown so that alfalfa can establish itself in the shadow of the oats.
This encompasses habitats or environments that are provided by companion plants for the benefit of insects that are beneficial (rather than harmful) to plants.
According to ATTRA, predators include ladybird beetles, lacewings, hoverflies, mantids, robber flies, and non-insects including spiders and predatory mites. Parasites include a wide range of fly and wasp species including tachinid flies and ichneumonid wasps.
Security Through Diversity
This is a more general approach that involves mixing crop varieties to at least ensure a yield from some of them. A fascinating example is the simple mixing of cultivars by University of California researchers who have shown that broccoli can reduce aphid infestation in certain crops.
Companion Planting Chart for Home and Market Gardening
ATTRA has compiled this simple chart from traditional literature the researchers have found on companion planting at home. It is designed to inspire you and me!
|Asparagus||Tomatoes, parsley, basil|
|Beans||Most vegetables and herbs||Onions, garlic, gladiolus|
|Beans (bush)||Irish potato, cucumbers, corn, strawberries, celery, summer savory||Onions|
|Beans (pole)||Corn, summer savory, radish||Onions, beets, kohlrabi,sunflowers|
|Beets||Cabbage and onion families, lettuce||Pole beans|
|Cabbage family||Aromatic herbs, celery, beets, onion family, chamomile, chard, spinach||Dill, strawberries, pole beans, tomatoes|
|Carrots||English pea, lettuce, rosemary, onion family, sage, tomatoes||Dill|
|Celery||Onion and cabbage families, tomatoes, bush beans, nasturtiums|
|Corn||Irish potato, beans, English peas, sunflowers, radish||Tomatoes|
|Cucumbers||Beans, marigolds||Irish potatoes, aromatic herbs|
|Eggplant (aubergine)||Beans, marigolds|
|Lettuce||Carrots, radishes, strawberries, cucumber|
|Onions family||Beets, carrots, lettuce, cabbage family, summer savory||Beans, English peas|
|Pea (English)||Carrots, radishes, turnips, cucumbers, corn, beans||Onion family, gladiolus, Irish potatoes|
|Potato (Irish)||Beans, corn, cabbage family, marigolds, horseradish||Pumpkins, squash, tomatoes, cucumbers, sunflowers|
|Pumpkins||Corn, marigolds||Irish potato|
|Radishes||English peas, nasturtium, lettuce, cucumbers||Hyssop|
|Spinach||Strawberry, Faba bean|
|Squash||nasturtium, corn, marigolds||Irish potatoes|
|Tomatoes||Onion family, nasturtium, marigolds, asparagus, carrots, parsley, cucumber||Irish potatoes, fennel, cabbage family|
|Turnips||English peas||Irish potatoes|
Promoting Good Relationships
Ultimately, successful companion planting relies on good relationships, often between pairs. Usually, one plant has the ability to do one thing, while the other offers something else. But sometimes it seems that certain plants simply do well together – like cheerful children who have special playmates. For example, parsley and asparagus generally both thrive when planted together. Tomatoes and basil also do well together, even if basil does not impart any flavor at all to the fruit of its tomato plant companions as some insist they do!
Fascinated? Why not give it a try and let us know how well companion planting at home works for you?