Plant Partnerships in Your Garden
What comes to mind when you hear the term partners? Perhaps you envision a healthy relationship between two people. Perhaps you think of successful business partners who work together. Perhaps you imagine satisfied co-workers who manage projects together. For gardeners, our attention turns to partnerships in the horticulture world. No matter which direction your mind goes, these phrases are likely to pop up: mutual support, beneficial association, and cooperative endeavor. Let’s dive in to learn more about plant partners in the vegetable garden.
A partnership is a relationship that entails cooperation between two entities with shared rights and responsibilities. Science-based data helps us understand how morphology, microbiology, and chemistry influence interactions among living things in your garden. To start with, envision your vegetable patch as a living ecosystem (Hemenway, 2009). Aim for your garden to be a thriving plant community with a variety of interrelationships that mimic nature’s rules (Cunningham, 1998). You might need to shift your view away from a neatly-engineered plot with straight rows of veggies toward a more natural-looking space with a varied collection of plants arranged to support beneficial partnerships. The goal? Purposeful plant diversity and plant companions as optimal neighbors in your vegetable garden.
You may have heard some of these phrases that refer to plant relationships. The following explanations will build greater clarity for these related techniques and principles.
Polyculture – This term suggests an agricultural system that includes a variety of unrelated plants occupying the same space (or garden), primarily to deter the spread of pests and diseases and amplify productivity (Chalker-Scott, 2015). As a gardening strategy, polyculture focuses on mutually beneficial relationships among plants, thereby increasing biodiversity to attract the “good guys” (beneficial insects) while confusing the “bad guys” (horticulture pests).
Companion planting – This term, one of the oldest gardening traditions, suggests pairing up different plants that seem to do well together, including vegetables, herbs, and flowers. The goal is to create a more productive garden based on the complementary physical characteristics of certain types of plants, such as size, growth habits, nutrient needs, and ability to resist pests. The example of “Three Sisters Gardens,” which comes from Native Americans, is probably the most well-known set of companion plants. In this case, planting corn, beans, and squash together works well. Rapidly-growing beans are nitrogen fixers, tall cornstalks support the beans that climb up them, and large, low squash plants discourage weeds and help retain soil moisture.
An issue with the companion planting approach is that it is considered an experimental field (Jeavons, 2021). Unfortunately, some recommendations for companion plants are not backed up by scientific evidence. Sure, tansy attracts ladybugs to a garden, and they dine on pesky aphids and other insect pests, but it’s best to have science-based data to explain what’s happening with those relationships. For example, Mexican marigolds are widely known as an effective deterrent for soil nematodes, so many gardeners plant their own favorite varieties of those flowers in vegetable beds. It turns out that some marigold varieties attract other pests, so this general recommendation for companion plants may not achieve desired results. Furthermore, to achieve the full benefit of nematode deterrence, marigold plants must be turned over and added into garden soil after the harvest.
Interplanting or intercropping – These terms refer to the practice of cultivating different varieties of plants in the same garden (or field), which conserves space. This method avoids the serious drawbacks of monoculture plantings that deplete soil nutrients and lure pests into their midst. Interplanting relies on particular reasons for whatever combination is chosen (Hemenway, 2009):
- Physical form and resource needs – Planting carrots next to onions and lettuce makes sense because of different root depths, leaf sizes, and requirements for sunlight.
- Growth and timing – Planting radishes, peppers, and lettuce near each other is useful because radishes grow and mature quickly, while peppers are slower to grow and ripen. The lettuce in-between them is happy for some shade.
The trouble with interplanting is that it just scratches the surface of why plant partnerships work, such as focusing on competition for sunlight. This method doesn’t go far enough to capitalize on the mutual benefits of certain plant partnerships, such as which plants repel which insect pests or help to decrease the incidence of plant diseases.
Cover crops – This well-known farming method is achieved when non-harvested crops, such as winter rye, buckwheat, or crimson clover are planted in the vegetable garden. Cool-season cover crops “cover” soil during chilly winter months. Warm-season cover crops “cover” soil before vegetable seeds are sown. They can also “cover” a fallow area of the garden. Cover crops provide many benefits, including improved soil structure and fertility, addition of organic matter, reduction of soil erosion, weed suppression, and habitat-creation for beneficial insects. Usually, cover crops are turned into the soil or mowed down before vegetables are added to those areas of the garden.
How Plants Influence Their Environment and Each Other
Remember that any plant cultivated in an outdoor environment will adapt to and change its surroundings. A plant will enact various survival strategies, and some of those actions may benefit its next-door neighbors. When two different types of plants benefit from this interaction in their local community, it’s called a plant association (Chalker-Scott, 2015)
Think of your vegetable garden as a well-balanced system with a multitude of connections. For best results, strive for beneficial associations through intentional planning. To determine which plants will be good neighbors, consider the following aspects of gardening.
All plants need nitrogen, which helps them develop leafy green growth. Some plants are nitrogen generators, and they are true heroes in the vegetable garden. Legumes, or members of the Fabaceae family, have the capacity for nitrogen fixation. They take nitrogen from the air and transform it into a form that plants can readily use. If you have beans and peas in your garden, those crops are adding nitrogen to the soil and sharing it with other crops. For optimal support, plant these helpful partners in close proximity to other vegetable crops and leave them in place after harvesting for added benefit to the soil.
To assist beans and peas in sharing nitrogen with their neighbors, the following are great partners to place in alternating rows (Walliser, 2020):
- Garden beans (green or yellow) and potatoes
- Fava beans and sweet corn
- Cowpeas and peppers
- Peas and lettuces
- Edamame and fall greens
Heavy or compacted soil is far from ideal for vegetable gardening. Fortunately, some plants help loosen soil, while adding nutrients and organic matter as they decay. As a cover crop, buckwheat is particularly effective for this purpose. Two other plants are excellent “bio-drillers” that handily break up heavy soil and open up channels for water and air circulation: turnips and forage radishes. Look for special varieties of these two vegetables with elongated taproots that can grow several feet down into the ground. They are champions for improving soil structure (Walliser, 2020), and in doing so, these bio-drillers create a beneficial partnership with the soil.
Every gardener feels the pain of all those unwanted green things that appear just about everywhere. Alas, no matter how hard we try to get rid of them, they return in full glory. One approach is to grow “living mulches” between and around the crops in your vegetable patch. These plants will block light from reaching the ground and help prevent weeds from sprouting. They also increase mycorrhiza in the soil, a beneficial fungus that supports plant health. You can plant living mulches between rows of veggies, around the base of crops (especially taller plants), or as walking paths in the garden. Great choices for this purpose are common thyme, white clover, and alfalfa, which tolerate foot traffic. A word of caution: if these plants get too thick, they will compete with crops for nutrients. You can cut back living mulches periodically, so they don’t grow out of control. Here are a few recommended living mulch companions (Walliser, 2020):
- Crimson clover and Cole crops
- Red clover and winter squash
- White clover and strawberries or blueberries
- White clover and tomatoes or peppers
Although most of us are quite familiar with the negative impact of insects on developing produce, let’s not forget about predatory species that consume other insects or parasitic creatures that feed and disable other insects. Be sure to include nectar-rich plants that attract beneficial insects to your garden, so they can do their good work of dining on unwanted critters. By partnering a plant prone to pests with a plant that lures in the predators of that pest, you’ll score a big win. The following pairings are well-suited to this relationship:
- Lettuce and greens with dill or fennel that offer desirable nectar to ladybugs, soldier beetles, damsel bugs, and parasitic wasps who zoom in to help control the aphid population
- Carrot-family herbs (dill, cilantro, fennel, anise) and mint-family herbs (sage, marjoram, oregano, rosemary, thyme, lemon balm) with vegetables that tend to have caterpillar problems. These herbs attract parasitic wasps that can take down pesky problem critters, such as unwelcome tomato hornworms.
- Cole crops, such as broccoli, cabbage, and cauliflower with lacy phacelia to control cabbage aphids. The lovely flowers of this plant attract bees and other pollinators, some of which are predatory insects that gobble up aphids.
A garden free of pests is impossible, but certain plant partnerships lend a hand in bolstering pest control. Insects find host plants through visual and chemical cues, so mixing up these cues with other plants can confuse potential pests. In “trap cropping,” vegetable crops are planted with companion plants that are purposefully “sacrificed” to insect pests, in order to save desired produce. In some instances, the trap crop can be located on the edge of the garden to keep pests away. This works well for potato beetles, squash bugs, and cabbage worms. In other cases, especially if pests are not highly mobile, the trap crop should be interplanted with the vegetable crop. This strategy is more effective for aphids, mites, and whiteflies. The following combinations have a good track record of success.
- Cowpeas for southern stink bugs – Stink bugs feed on tomatoes, beans, and peaches, but if cowpeas are planted a few feet away, you can collect and dispose of them before they get to those veggies.
- Blue Hubbard squash for squash bugs and vine borers – These destructive insects prefer blue Hubbard squash over other squash, as well as pumpkins and melons. By planting a blue Hubbard squash on the periphery of your garden 3-4 weeks ahead of the other crops, you will lure squash bugs and vine borers away from other squash varieties, pumpkins, and melons.
- Radishes for flea beetles – Adult flea beetles are notorious for wreaking havoc on many crops by chewing on the leaves, and their larvae nibble away on roots underground. It turns out that their preferred veggie is radishes. By interplanting radish seeds ahead of when the other crops will mature, you can save most of your peppers, tomatoes, potatoes, and Cole crops.
In some pairings, one type of plant will “mask” the chemicals that attract insect pests to a particular crop, thereby limiting damage to that host vegetable. Studies have shown that these combinations work well to reduce pest problems in a vegetable patch (Walliser, 2020).
- Zucchini or summer squash and nasturtiums to deter squash bugs –Look for bush-type nasturtiums if your space is limited, and try the vining type of nasturtiums that will surround squash plants if you have ample garden area. Colorful nasturtium flowers are edible, an added bonus, and they attract beneficial pollinators.
- Peppers and allium plants to alleviate problems with green peach aphids (which carry plant viruses) – Onions, scallions, and garlic have the power to keep highly destructive aphids off your prized pepper plants.
- Tomatoes and basil to keep thrips away – The scent of basil masks the scent of tomato plants, discouraging thrips from landing on tomatoes and bringing unwelcome diseases.
- Collards and calendula to prevent aphid infestation – Aphids love collards (and most Cole crops), but calendula is an effective deterrent that can save your crop from devastation.
Potatoes and catmint to deter Colorado potato beetles – When planted right in your potato bed, the fragrance of catmint helps to drive away potato beetles from feeding on those plants.
Another pest management strategy reflects the “resource concentration hypothesis,” which suggests that insect pests have a tougher time locating preferred host plants when there is greater diversity in a garden bed. In other words, if you embrace polyculture in your vegetable garden, the insect pests may have trouble figuring out where they want to hang out and cause damage.
Summing It Up
Truth be told, I got quite excited when researching this topic because my vegetable garden has struggled with many of these issues. As a proponent of organic farming, I refrain from use of toxic chemical controls on vegetables for human consumption. Now, I have high hopes that effective plant partnerships will minimize or help to resolve the contentious problems that interfere with a bountiful harvest of healthy produce. I’ve redesigned my garden plot with an eye for mixing things up and the inclusion of more carefully-selected flowers and herbs. I’ve decided to be comfortable with a slightly untamed look that more closely represents nature. I’m looking forward to observing my garden as it is transformed into a diverse, self-sustaining system. And I’m delighted at the notion of plant partnerships that can take on some of the work required to maintain a thriving community of edible crops.
Resources in Print (recommended books on this topic)
Chalker-Scott, Linda. (2015). How Plants Work. Portland, OR: Timber Press.
Cunningham, Sally Jean. (1998). Great Garden Companions. Emmaus, PA: Rodale Press.
Gillman, Jeff and Maynard, Meleah. (2012). Decoding Gardening Advice. Portland, OR: Timber Press.
Hemenway, Toby. (2009). Gaia’s Garden. White River Junction, VT: Chelsea Green Publishing.
Jeavons, John. (2012). How to Grow More Vegetables. Berkeley, CA: Ten Speed Press.
Walliser, Jessica. (2020). Plant Partners. North Adams, MA: Storey Publishing.
Guidance from the University of Minnesota Extension Service
Recommendations from the University of Massachusetts at Amherst
Suggestions from the Penn State Master Gardener Program in Susquehanna County
Which vegetables grow well together and which pairings don’t do so well together