Improve Soil Health with Nitrogen-Fixing & Groundcover Plants
Companion planting can improve your garden soil’s overall health, nutrient availability, soil structure, and moisture.
Leguminous plants fix nitrogen (N) into the soil through a symbiotic relationship with Rhizobium bacteria. Inside nodules on the legume’s roots live these bacteria. They convert atmospheric nitrogen gas into ammonia, which plants in the soil can take up.
Certain crops can benefit from legumes’ nitrogen-fixing abilities. For example, beans can help fix N into the soil, which benefits heavy-feeding crops like corn. The corn then provides a place for the beans to grow vertically on its stalk.
Radishes can be grown to aerate compacted soils. These deep-rooted vegetables can act like a broad fork, loosening the soil and creating pore spaces for proper air and water movement.
Keeping the soil covered by plants year-round helps to hold soil in place to prevent topsoil loss and allows for proper air and water circulation within the soil. Soil will not be lost to wind or water if held in place by plant roots.
The soil will also be kept cooler and more consistently moist if shaded by plant leaves. Vining plants like squash and pumpkins help shade the soil, especially in times of drought. For more information on improving soil health, see HGIC 4 Ways to Improve Your Garden’s Soil Health.
Marigolds (Tagetes sp.) are being grown as companion plants with different varieties of eggplants (Solanum melongena).
Julia Nichols, ©2025, Clemson Extension
Maximize Garden Space with Companion Planting Techniques
Companion planting helps gardeners and growers utilize all their available growing space by maximizing the number of plants in one area, which is ideal for growers with smaller growing spaces.
For example, instead of just growing carrots in a raised bed setting. Plant carrots and radishes together. This utilizes all the growing space with more to harvest. The radishes will be harvested first, and their leaves will help keep the soil covered and cool for germinating and growing carrots.
Radishes can even be planted successively to get a few harvests before the carrots are ready. The radishes help aerate the soil at a shallow level, while the carrots do the same at lower soil levels.
Growing herbs with a compact growth habit around your vegetable plants is a great way to use the entirety of your growing space. Basil, chives, parsley, oregano, sage, dill, and cilantro generally don’t require much space to grow, so they can be placed around the edges of beds or vegetable plants.
Control Pests Naturally by Attracting Beneficial Insects
The best way to keep insect pests at bay is to attract their predators to your garden space. Certain plants and flowers attract ladybugs, lacewings, and parasitic wasps. These insects help keep pest insect populations (aphids, whiteflies, caterpillars) low in your garden. For more information, see HGIC 1721, Incorporating Beneficials into the Gardener’s Toolkit.
Some examples: marigolds repel nematodes in the soil; onions can deter carrot flies, while carrots help improve the growth of onions; basil repels tomato pests, and although it has not been proven, many gardeners believe planting basil and tomatoes together improves their flavor.
For more information, see HGIC Can Plants Repel Problematic Insects?
Basil plants (Ocimum basilicum) are being grown alongside determinate tomatoes (Solanum lycopersicum) to repel pests.
Julia Nichols, ©2025, Clemson Extension
Suppress Weeds with Dense Companion Plant Growth
Companion plants can create a more dense and hardy plant community, which can outcompete weeds for resources like water, sunlight, and nutrients.
Thick foliage and lush growth habits can shade the soil, preventing germination of weed seeds. Create a physical barrier inhibiting weed germination with borage and marigolds. They are known for their thick foliage that can act as a ground cover and suppress weeds and their seeds. Both are excellent companion plants for tomatoes and peppers, too.
Boost Harvest and Pollination with Flowering Companions
More pollinators mean increased pollination, which can improve crop yields. Many vegetable crops are not self-fertile. They rely on pollinators to grow their fruit. Melons, berries, zucchini, and winter squash are some examples.
Adding pollen-rich flowers to your growing space, alongside your vegetables, is the best way to attract pollinators. Calendula, zinnia, borage, and cosmos are all excellent choices for this. For more information, see HGIC 1727, Pollinator Gardening.
Avoid Common Companion Planting Mistakes
Plants have ‘friends’ that can be planted beside each other for beneficial reasons. They also have ‘foes’ that should avoid sharing the same space.
Some plants can compete for the same resources and attract the same pests. For example, kale, cabbage, and cauliflower should be planted away from each other. They all attract cabbage moths and can create a cabbage moth caterpillar infestation.
Dill can stunt the growth of carrots, and the two can cross-pollinate since they are in the same family, producing inferior hybrid plants if you plan to save the seeds for future plantings.
Corn and tomatoes both attract corn earworms. Planting near each other can make it easier for the pest to spread and infest these crops.
