Companion Planting for Soil Health

Plant relationships have evolved together to help maintain ecosystem health, and this is especially true under the soil. We can practice companion planting to grow more resilient gardens.

At its core, companion planting is the practice of planting different plant species together for their mutual benefits. It’s all about understanding a plant’s needs and gifts so we can help them share resources and boost harvests.

*This is part of an award winning article originally published in Fall 2025
Northern Gardener Magazine*

Companion Planting Benefits

• Healthier Soil
• Suppressed Weeds
• Balanced Pests + Diseases
• Increased Beneficial Insects
• Increased Harvests

Modern companion planting focuses on planting biodiversity. Beware simple companion planting equations of A + B = C. Nature is too sophisticated and raucous a partner to play by such simple human inventions. Luckily, scientific research continues to increase and begs to be put into action in our gardens. However, each garden is made up of infinitely diverse relationships, so observation in your own space is always best.

Planting biodiversity leads to beauty above ground along with welcoming diversity below ground. Plants release different chemicals in the soil around the roots (the rhizosphere) specifically to attract different microorganisms- thus shaping their surrounding soil ecosystem. Diverse planting also grows the most beautiful gardens, so it’s a win-win.

I have you covered too, if you want to focus on flowers for companion planting.

Stronger Soil

Soil health depends on a long history combined with what’s currently growing and decomposing in any area. But when we treat it well, the health of the soil continues to improve, becoming truly resilient. One of the big players in plant health are mycorrhizae, you may have seen these fine white webbing threads under wood chips, they’re the fungal hyphae that connect plant roots to more nutrients in the soil. They form symbiotic relationships with plants, responding to their requests for specific nutrients. Mycorrhizae mine these nutrients from much further away than plant roots can, bringing the nutrients back to the plant in return for carbohydrates—thanks to plants’ ability to photosynthesize.  Knowing these yards of networked fungi are gathering nutrients under the soil is another reason to minimize soil disturbance with No Dig practices.

But fungi aren’t the only biology living in the soil. There are over 10,000 identified species including fungi, bacteria, algae, nematodes, protozoa, algae, spring tails and earth worms. They each have their own jobs to do while working together in way more eloquent way than our understanding of NPK comprehends. The soil ecosystem, teeming with around 1 billion of these microscopic organisms, is also in constant communication, releasing and absorbing chemicals and electrical impulses.

Nutrient Accumulators

Vegetables are notorious for being heavy feeders, requiring lots of nutrients from the soil. We’ve been told to add the nutrients back to our soils with bags of specific chemicals. But many plants naturally collect more than enough to share with their neighbors.

Using the nitrogen accumulating abilities of legumes like peas, beans and clovers is a good place to start. Through a symbiotic relationship between bacteria (rhizobium) and nodules in the roots they convert atmospheric nitrogen into an ammonia. The roots of legumes form special nodules that collect this converted gas. Next, nitrates are formed, which can be absorbed by plants.

Accumulating Plant Options

• Yarrow (Achillea millefolium) collects potassium, calcium, and magnesium.
• Lambsquarters (Chenopodium album) – collects potassium.
• Comfrey (Symphytum peregrinum) – collects calcium.
• Common Nettle (Urtica dioica) collects calcium

Some plants are good at gathering nutrients from deep underground. These are called ‘dynamic accumulators’ because they reach down into the subsoil and draw nutrients up into their stems and leaves. We can then ‘chop + drop’ these stems and leaves, letting them decompose on the soil’s surface, re-releasing the nutrients to other plants.

A Planting Plan

• Plant tomatoes and half runner beans along a sturdy trellis.
• Plant celery and basil alternately at the base of the beans and tomatoes.
• In front of the celery and basil, plant a thick row of carrots.
• In front of the carrots plant sweet alyssum.
• Add marigolds to the corners of the planting area.

The more we understand plant relationships, the more we can see the genius of nature on display- even without a microscope. The results show in our garden spaces buzzing with life, the beautiful harvests and resilient plants.

Hoping these ideas invite you to plant more companionably.

*Originally published as part of an article in the Fall 2025 issue of Northern Gardener Magazine. Now awarded the Gold Laurel from Garden Communicators International.

Dig In,
Michelle