Companion planting is the age old (literally from the start of human agriculture) practice of intentionally growing species together that provide each other mutual benefit.

The classic example most Americans learn about is the Native American’s “Three Sisters”, the growing of Maize (corn), Beans, and squash together. The corn provides a trellis for the bean vine and provides needed partial shade for the squash; the bean imbeds nitrogen into the soil and adds extra strength to the corn stalk; and the squash blocks out any weeds and keeps moisture in the soil. Nutritionally, it is also a brilliant method as eaten together they give the human body a complete protein.

This practice extends beyond just agriculture (though this is where you see it most often intentionally practiced). Looking at our native ecosystems, you see natural examples of this everywhere, where species evolved together providing mutual benefit.

Why you should care:

Knowing these companion relationships allows us to use natural systems to our advantage.

This obviously saves us time, money, headache, etc…

I have compiled a list of the most common companions below from multiple sources. It should be noted that the scientific research on these is minimal at best. Many of these tend to be Farmer’s Almanac style tips. Many also tend to be good food pairings, so there might be some overlap there.

That being said, non-practical farmers don’t tend to succeed. So if they’ve worked well enough to be used long term, there’s likely some benefit.

Hostile Pairings:

There are of course plant species that do not get along. Either due to an evolved defense / competitive advantage mechanism or simply a fluke of biology, having these species planted near each other can stunt the growth or outright kill one or both. (ex: very few species can survive near a Black Walnut Tree, as they release Juglone, a very powerful anti-plant toxin).

I have included a list of the most common known problematic pairings below. These tend to be “slightly” more researched than the companions, simply because its easier to objectively measure survived vs didn’t survived than different degrees of "thriving”. (also, toxins are pretty straight forward to test for). That being said, same Farmer’s Almanac rules apply.

Note: Some of these hostile pairing are due to known pest attraction (eg. one plant species attracts an insect that destroys another). In these cases, the solution is not to avoid planting them in the same bed, but, either choosing to only plant one of the species that year, or planting them a significant distance apart (think 100+ feet).

A good example of this are corn & tomatoes, both of which are fed upon by the Helicoverpa zea caterpillar, known commonly as both the Corn Earworm and Tomato Fruitworm. Having both plant species close together makes a very attractive target for the moths to lay their eggs, and therefore the caterpillars to eat your plants.

How To Companion & Hostile Planting:

Companion Planting Guide: Plant 1 companion for every 6ish target plants, ideally in close proximity, in the same bed

Hostile Planting Guide: For most hostile pairings, you can simply not plant in the same bed to avoid issues. Some like Dill & Carrots need to have significant separation as they cross pollinate, leading to poor crops

To save you time clicking to the guide for the most common planting…..

Tomatoes / Peppers / Eggplants

*All three are of the nightshade family, and suffer from the same diseases. Make sure you do not plant nightshades in the same soil over successive years, as their diseases live in the soil, and will infect future nightshades. (e.g. rotate your planting every year between beds).

Nightshade diseases will die in soil in 1 - 3 years if no host plants are planted. If your plants have become actively diseased, wait the maximum or replace the soil before planting nightshades in that site again.

Hostile Pairings

Companion

• The Brassica Family:

  • Broccoli, Brussels Sprouts, Cabbage, Collards, Cauliflower, Kale, Kohlrabi, Rutabaga, Turnips

• Corn

• Fennel

• Amaranth

• Basil

• Borage

• Carrots

• Garlic

• Marigolds

• Nasturtium

• Onions

• Parsley

• Spinach, Lettuce, Chard - all crowd out weeds

*Dill deserves a call-out: as a young plant it is a helpful companion, but once it flowers, it is detrimental to nightshades. Unless you have time to prune it every week (to keep it from flowering), I wouldn’t bother planting in the same bed.