Hundreds of online articles offer information on which crops grow well together and which crops you should avoid planting near one another. Is it a garden fad, or does companion planting really work?
This popular gardening trend has ancient roots with actual scientific backing. It may seem overwhelming due to the sheer number of possible plant combinations and all the information out there. But let the possibilities excite you!
The science-backed benefits of companion planting can revolutionize your garden. Here is the science of companion planting, its potential benefits, and how to use it in your garden.
Scientific Research
Science proves that some species are mutually beneficial when grown together.
Companion planting is intentionally growing multiple crops together to positively affect each other. For example, studies show that marigolds intercropped with kale can dramatically reduce aphid populations by attracting predatory syrphid flies and parasitic wasps
The well-researched benefits of different plant combos include the following:
- Attracting beneficial insects: Studies show that companion plants attract the natural enemies of many garden pests.
- Increasing biodiversity: Ecological science has repeatedly shown that more biodiversity creates greater resilience against insects, pathogens, and climatic threats.
- Deterring damaging pests: Monoculture means growing many of the same crop plants in one space. In contrast, research shows that polyculture (companion) plantings reduce pest pressure. More plants mean it’s harder for pests to find their hosts.
- Providing nutrients to the soil: Studies indicate that leguminous plants improve the growth of neighboring non-legumes by fixing nitrogen into nodules on their root systems. The underground nitrogen transfer depends on soil conditions like moisture and microbial activity. Still, even without that transfer, as the root systems decay after the season ends, they release nitrogen into the surrounding soil.
- Prevent diseases: Studies show that planting a specific onion type (the “potato onion”) with tomatoes can help inhibit soil-borne diseases like Verticillium wilt.
- Camouflaging the scent of a crop: The pungent smell of herbs and allium crops can mask the scent of many crops. For example, research shows French marigolds are highly effective root-knot nematode repellents above and below ground.
- Improve soil conditions: Some plants are sensitive to the soil’s pH, mineral content, or salt levels. For example, strawberries are salt-sensitive. Research shows that halophytic (salt-loving) purslane as a companion plant can improve strawberry yields and fruit quality.
History
While it seems like a popular modern buzzword, this method has been around for centuries. It likely originated 8,000-10,000 years ago with three sisters plantings.
Indigenous people discovered they could grow squash, beans, and corn together in the same space, and each crop benefitted the other two. The trio of crops was also a vital part of their nutritional diet. The strategic process happened like this:
The corn was sown and mounded up for several weeks. When the corn germinated and began growing, indigenous women would plant bean seeds at the base. The cornstalks grew tall and offered support for the beans as a trellis.
Squash or pumpkins were sown in between the rows of mounds containing corn and beans. The vines of the squash covered the ground and helped to decrease weed pressure. In addition, they shaded the ground, which helped maintain moisture in the soil.
The beans naturally fertilized the corn and squash after converting nitrogen into nitrates. These three crops grew better together and nurtured each other the way a family would, hence the nickname, the three sisters.
Companion Planting vs. Intercropping
Companion planting emphasizes intentional garden benefits, while intercropping promotes beneficial interactions between multiple crops.
While some people use these terms interchangeably, there is a slight difference. As a small-scale organic farmer, I grow intensively on small-scale garden plots, so taking advantage of every inch is very important for us.
However, everything we “intercrop” is not necessarily for an intentional garden benefit, which is usually the case for companion planting. Rather, intercropping is out of necessity to save space.
The University of Tennessee Extension makes this distinction:
- Companion planting promotes some sort of cultural benefit, such as pest control.
- Intercropping is growing two or more crops near each other to promote beneficial interactions, such as increased biodiversity.
How Companion Planting Works
As you’ve learned, companion planting has scientifically backed benefits.
Attract Beneficial Insects
Attract beneficial Braconid wasps by planting native flowers and herbs near tomato plants.
Planting tomatoes with flowering herbs is a classic example of companion planting for attracting beneficial insects. The parasitic Braconid wasp lays its eggs on the body of the tomato hornworm, one of the most damaging tomato pests.
When the eggs hatch, the wasp’s larvae consume the hornworm from the inside out, ensuring it no longer feeds on your tomato plants. Attract these parasitic wasps by planting native flowers such as asters and small-flowering herbs such as cilantro and dill.
You will have created a little ecosystem in your garden by providing the wasps with a constant supply of pollen and nectar to feed on. Instead of suffering at the hands of the hornworm or needing to use outside pest control inputs, take advantage of natural pest control created by Mother Earth!
Pro tip: This technique also applies to attracting pollinators, in general. If you are not getting high yields of a crop like cucumbers, eggplant, or tomatoes, try planting borage and other colorful flowers in clumps so bees and butterflies can easily spot them.
Repel Pets or Attract Them Elsewhere
Planting green onions and French marigolds in specific locations in the garden can deter deer, slugs, and Japanese beetles.
The pest-deterrent benefits of this method are tried-and-true in scientific studies and real-life circumstances like my farm. There is a reason I always plant a row of green onions down the center of a head lettuce bed or why I plant French marigolds near my peppers.
The scent of onions and marigolds can deter damaging deer and slugs. The marigolds might also serve as a trap crop for Japanese beetles, which notoriously destroy my zinnias.
I only grow marigolds as a trap crop. So if they are destroyed, they have served their purpose, especially if the beetles stay away from my zinnias!
To deter pests, you can strategically grow other strong-smelling herbs and flowers around your garden plot. For instance, the strong scent of basil may help mask the scent of peppers and tomatoes, making it more challenging for pests or wildlife to find them.
Complimentary Root Systems
Pairing carrots and tomatoes as companions benefit both plants.
The effects also happen beneath the surface. We all know how important it is to keep our soil from eroding. Hosting different crops within the same garden bed provides different root system formations, helping to keep soil in its place.
Also, when you plant something like squash which needs to be spaced out quite a bit, there is lots of empty soil until the plants spread out. Try planting something in the empty space to help anchor the soil and discourage weeds while the squash grows.
Another successful yet unexpected companion duo is carrots and tomatoes. Tomatoes are sun and heat-loving, whereas carrots prefer a bit of shade. Sow carrots alongside your tomatoes to relieve them from the hot summer sun.
Carrots will also help aerate the soil and allow the deep roots of tomatoes to receive more water and nutrients, especially after they are pulled. The carrots act as sort of a natural till to the soil surrounding the tomatoes.
Enhance Soil Biodiversity
Diverse gardens support healthy ecosystems with essential soil organisms.
The more diverse your garden is aboveground, the more diverse your soil will be underground. This creates a healthy cycle of pest and food, life and death.
Earthworms, fungi, and good bacteria are extremely vital to the overall health of the fruits, vegetables, and flowers you grow. Call them the unsung heroes of the plant world.
They help aerate soil and intake nutrients, break down organic matter, and sustain plant life by providing nutrition. Healthy soil helps sustain healthy gardens and, in turn, healthy families.
Monocropping is essentially the opposite of companion and interplanting. The same crop on the same plot depletes the nutrients from the soil and repeatedly attracts the same pests.
This causes dependence on amendments, sprays, and in many cases, heavy tillage. These destroy beneficial nematodes and the structure of the soil, forcing mono-crop growers to start from scratch each season.
How to Companion Plant
Planting mutually beneficial crops doesn’t have to be complicated. Just be sure you consider each crop’s mature size and growth habits.
Start Simple
Experiment with easy companion plant combinations like dill with cucumbers to deter pests and attract pollinators.
Here are a few easy combinations you can try this season:
- Sweet alyssum alongside tomatoes keeps weed pressure down by forming a cascading carpet of flowers. The flowers then attract beneficial insects that feed on aphids.
- Dill with cucumbers will help attract pollinators which could result in higher cucumber yields.
- Sage near strawberries could help mask the sweet berry scent from critters like bunnies or birds.
Our in-depth companion planting guides are a great place to start for discovering the right partners for specific crops. You can try more complex options once you get the hang of it.
Take Notes
Keep notes when planting multiple crops together, as unexpected outcomes may arise, such as accidentally attracting Japanese beetles.
Sometimes trying a new method creates a different issue you hadn’t thought of until you try it, so taking notes is important. You could, for example, attract Japanese beetles to a crop they hadn’t been interested in before by planting marigolds nearby. Or you could mistakenly plant two crops together that surprisingly create a great outcome, and you’ll want to remember that too!
Every action has a consequence, and every change you make in your garden will have some effect, either positive or negative.
Experiment
Planting radishes with summer squash and cucumbers yielded a small win.
This spring, I planted radishes alongside our summer squash and cucumbers. We noticed the tops of the radish greens were getting chewed a bit, the squash and cucumbers less so.
The radish greens had small bite marks. Though not great for a farmers’ market display, it’s preferable to a decimated cucumber plant. I deem this a small win.
Radishes are a super quick crop, so there’s no fear of them taking too much from the soil. Their roots don’t go down far enough to disturb squash or cucumbers.
The jury is still out on whether basil and marigolds enhance the flavors of some vegetables, but if they grow well together and it works in your garden, why not give them a shot? No harm done and possibly great benefits.
Does it Work?
Use this method to maximize space and control weeds.
There has been lots of research over the years, and much of the data shows that companion planting works. Even if some evidence is anecdotal or may seem coincidental, other results are well documented. Although not conclusively, companion planting works in many circumstances.
Whether or not you believe in a flower’s ability to enhance your crops, you can take advantage of the space you have. Intercrop shorter-season crops alongside your summer squash, which allows you to get two crops out of one space.
The radishes are quick, low-maintenance, and don’t take much from the soil while keeping weed pressure down. The radishes have long since been enjoyed once the squash plants start to vine out. Everyone wins!
And, once again, the benefits of abundance in biodiversity are irrefutable. The simple thing to remember is: If you have aphids, you need ladybugs, green lacewings, and soldier beetles. If you have a hornworm issue, you need Braconid wasps. Your best bet is to grow things that attract those things.
Final Thoughts
While there is nothing 100% certain in nature, as there will always be unexpected factors playing a role in how things grow, I encourage you to give companion planting a shot. In most cases, you’ll find something that works well for you in your growing region and your specific plot.
Mother Nature built in some pretty awesome growing hacks, and we will start noticing them if we slow down and look around. I urge you to try strategically planting crops together so you don’t miss out on the potential benefits of higher yields, decreased pest pressure, and utilizing your space to the best of your ability.
