What companion planting is teaching me about choosing plants with a purpose
I just finished putting together our Re-Fresh cover crop termination guide, and after spending so much time thinking about how to end a cover crop, one idea kept coming back to me:
Before you plant something, it helps to know how you plan to finish it.
Every plant we intentionally put into the garden comes with a next step. Will it die with frost? Will we cut it? Leave the roots? Incorporate the top growth? Could we let it grow too long and end up with seed and volunteers next season?
Cover crops are planted for a purpose, but they also need a plan.
And lately, I’ve been thinking that maybe we should look at more of our garden this way.
Plants Have Relationships
I love Indian paintbrush.
Its vibrant reds and oranges stand out against the muted colors of our desert landscape, and I point it out to my family almost every time I see it.
But what fascinates me most about Indian paintbrush isn’t its color. It’s what is happening underground.
Indian paintbrush is a unique plant because while it can make its own food through photosynthesis, its roots can also connect with the roots of neighboring plants and take in water and nutrients from them.
What looks like one beautiful wildflower growing on its own may actually be participating in a relationship we can’t see.
That fact has always stuck with me.
Plants don’t necessarily operate as little islands.
Sometimes what is growing beside them matters.
The Marigolds I Never Forgot
Years ago, while traveling in Europe, someone told me that after a strawberry field was removed, they would sometimes rotate marigolds into the field.
I remember thinking, marigolds?
That seemed like something you planted around a flower bed, not something a grower would intentionally plant across a field.
But there was a reason. The marigolds weren't being grown for their flowers. They were being used as part of managing the soil and certain pest problems before another crop was planted.
That trip was also important to me for another reason.
It was the year I came home wanting to figure out how to bring cover crops out of the field and into the backyard garden.
I was beginning to look at agriculture differently. I wasn't only paying attention to what farmers were growing to harvest. I was paying attention to what they planted between crops, alongside crops, and sometimes simply because that plant had a job to do.
So the marigolds stuck with me.
A plant can earn its place because of what it contributes to the system, even when it isn't the crop we're trying to harvest.
That idea eventually became a big part of Re-Fresh.
This year, I planted marigolds alongside my tomatoes.
Like a lot of gardeners, I had heard that marigolds and tomatoes were good companions. But if I’m truthful, I planted them because I had heard they were beneficial. I didn’t spend much time asking exactly why.
Now I am.
What are those marigolds actually doing?
Which benefits have research behind them? Which depend on a particular pest or the way the plants are being used? And which pieces of companion-planting advice have simply been passed from gardener to gardener?
Those questions have become much more interesting to me than a list telling me which plants are supposedly “friends.”
Then Buckwheat and Dahlias Popped Up
Recently, we’ve been seeing posts about dahlia growers using buckwheat as part of their approach to wireworms.
Of course, that caught my attention.
There is research looking at buckwheat and wireworm management, and studies have found reduced wireworm damage in certain cropping systems involving buckwheat. But the relationship is more complicated than simply saying buckwheat repels wireworms or draws them away from another plant.
And that distinction matters.
It would be easy to see a post about buckwheat and wireworms and think:
I have wireworms. I should plant buckwheat with my dahlias.
But after spending so much time working on our termination guide, my next thought is:
And then what?
Buckwheat grows quickly. It flowers quickly. And if we allow it to mature and produce viable seed, we may end up with volunteers that we'll need to manage later.
That doesn’t make buckwheat a bad choice.
It means we need a plan.
Why are we planting it?
What do we expect it to accomplish?
How are we going to manage it while it grows?
And when its job is finished, what are we going to do with it?
Not Every Neighbor Is a Good Neighbor
There is another side to plant relationships too.
Sometimes having certain plants growing near one another can create an unwanted opportunity.
Pear trees are a good example. Some pear rust diseases rely on another plant, such as certain junipers or cedars, to complete their life cycle. When both hosts are present in an area, the disease has what it needs to keep moving through that cycle.
Neither plant is doing anything wrong. It is simply another reminder that what grows around a plant can matter.
Sometimes that relationship can be useful.
Sometimes it can be harmful.
Sometimes it may make very little difference at all.
Which makes me wonder if we’ve been asking the wrong question about companion planting.
Maybe Companion Planting Is the Wrong Question
The more I learn about this, the less interested I am in memorizing lists of “good” and “bad” companion plants.
I’m much more interested in asking:
What does this plant contribute?
One plant might provide flowers that support pollinators and beneficial insects.
Another might fix nitrogen.
Another may produce a lot of biomass.
Another may cover bare soil.
Another may have a root system that explores a different part of the soil.
And sometimes a plant may have a very specific relationship with a pest, disease, soil organism or another plant.
Those functions aren't interchangeable, and neither is the research behind them.
That means we should be careful with sweeping statements like “this plant repels pests” or “these two plants grow better together.”
Sometimes there is good research behind a relationship.
Sometimes the research applies only to a very specific situation.
And sometimes we may simply be repeating garden wisdom without knowing where it came from.
I don't think that means we should stop experimenting. Curiosity is one of my favorite parts of gardening.
But I do think we should understand why we're planting something.
Plant With a Purpose
And that brings me right back to cover crops.
When we build a cover crop mix, we aren't simply trying to fill an empty space with green plants. Different species are selected because they bring different characteristics to the mix.
But choosing the plant is only half of the decision.
We also need to know how we're going to manage it.
Maybe that's a good approach for the rest of the garden too.
Before adding a plant because someone says it's a “good companion,” ask what you want it to accomplish.
Find out what you can about why the relationship works.
Think about how you're going to manage it.
And have a plan for what happens when its job is finished.
I’ll probably always point out Indian paintbrush when I see it. I love the vibrant color against our desert landscape, but I love the story happening underneath it even more.
It reminds me that there is often more going on in a community of plants than we can see.
Maybe the lesson isn't simply that plants need good companions.
Maybe it's that every plant we add changes the community in some way.
So don't just ask what a plant produces.
Ask what it contributes. And have a plan for it.
Farm Wisdom
Every plant needs a purpose and a plan.
Before you plant it, ask what you want it to do. And before it grows, know what you're going to do when its job is finished.