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Every time I see mallow and oxalis growing in my greenhouse, I’m caught in a tug-of-war between annoyance and understanding.
Truth is, as a gardener, I don’t want to see these uninvited plants getting too cozy. Especially in soil that I have reserved for other plants.
But as a land steward, I’m always taken back to an interview I watched a few years back, where Farmer Jesse from No-Till Growers interviewed Helen Skiba of Artemis Flower Farm. Based in Colorado, her farm is on clay soil in a dry climate.
“My philosophy with weeds is [that] they’re there for a reason - there is a reason. With the mallow, it’s aerating my soil, it’s also a big spreader so it’s covering the soil. I can tell that the soil needs cover because of the weeds that are here. They’re broad-leaf, covering the ground kind of weeds, so that’s telling me what the soil is asking for.”
Just yesterday, I was reminded of this when I was pulling some mallow from both my greenhouse and regular in-ground rows. The taproot on the mallow of some of these plants was around 10 inches long!
It’s kind of funny, because here I am, actively working on reducing compaction in my soil, enriching the clay with organic matter, trying to protect the soil during our extra wet winters and our very dry summers.
Maybe you’re like me in this very modern way of thinking it’s all my hard work making the change.
But, it’s moments like seeing a 10 inch taproot appear out of nowhere that I’m reminded that nature is helping me too.
The soil is communicating with me about what it needs/wants through the plant and animal helpers that it calls upon. At the same time, when I notice something is lacking, the soil is communicating with me too, asking for help.
Are you willing to listen to the soil and collaborate with it?
While clearly, the soil doesn’t have a voice, but if you pay close attention, you can start to translate its signals into actions you can take to help out your garden.
Keep reading to become a soil signal interpreter.
But First: Do You Have Any of These Misconceptions About Indicator Plants?
Before you get into soil diagnostics mode, there are a few myths we should get out of the way so you can better understand the soil signals these plants are providing.
Soil Conditions Aren’t Uniform: The presence of a single wild plant doesn’t tell the full story of your whole garden.
Removal Doesn’t Bring Soil Health: Removing weeds doesn’t improve soil health on its own - you need to address the underlying conditions.
Soil Conditions Can Be Changed: Don’t despair if you learn that your soil is compacted, alkaline, or lacking a nutrient. You can take action to improve the overall quality of your soil for yoru garden.
Now you’re ready to transform weeds into wisdom about the soil in your backyard.
What Plant Characters Are a Part of Your Yard's Story Arc?
Sean of Edible Acres calls plants characters, a term that feels fitting here to help us think about weeds like characters in a book - they have personalities, motives, and they act based on cause and effect.
Like finding similar words in a thesaurus, often wild plant characters will show up in agreement of a soil signal.
Don't worry - there are solutions!
For example, both mallow and oxalis spread through my greenhouse and cover the soil to remind me that mulching is important in the greenhouse, especially in the summer with increased water evaporation.
Indicator Plant List:
Have a look through this plant list to see if you notice any familiar friends. It's a sortable list so you can rearrange the plant names by alphabetical order forwards and backwards.
Self-Heal indicating acidic soil - perfect spot to grow Creeping Raspberries and Strawberries!
What I’ve noticed in my own garden:
Acidic & Shady Soil Conditions: Wild strawberries, sorrel, cleavers and blackberries are growing in an area where food crops weren’t performing well. I realized these weeds were indicators of acidic & shady soil conditions. Instead of trying to shift things, I turned this into a solution by planting acid-loving understory berry bushes here.
Compacted Soil: Curly dock, mouse ear chickweed, creeping buttercup, dandelion, geranium show up in my garden pathways as a reminder of the compacted soil that I’m working on remedying. The more I tend to the soil, the less I notice these indicator plants showing up.
Rocky or Bare Soil: I notice hawkweed (cat’s ear) grows well in areas where the soil is still healing, and grass isn’t growing well. These areas are otherwise patchy, rocky, and dry.
Wet Soil: In an area of woodland that is moist most of the year, marsh hedgenettle and violets grow in abundance. Our native Cluster Rose grows well here, too.
High Nutrients: There’s an area in my yard where the previous owner piled horse manure. This spot is full of crane’s bill geranium, chickweed, purple dead nettle, which show up as a reminder of this wealth of nitrogen.
Burn Spots: In areas where the previous owners had burned debris, I’ve noticed an interesting succession of plants. First, thistle and St. John’s wort dominated these spots, but after a couple of years they disappeared completely and these areas have been replaced with clover and other non-invasive forbs.
Tons of Crane's Bill Geranium in my yard, on top of an old horse manure pile
How Can You Resolve These Soil Issues Sustainably?
Here are some simple (and regenerative!) remedies for restoring your soil's health based on the indicator plant species you've observed.
Yellow Wood Sorrel indicates dry soil, which I'm working on remedying with manure and straw mulch
Tips for Understanding Indicator Plants in Your Garden
Keep a Garden Journal: Notice the presence of indicator plants throughout the year, create a map and notice patterns. This will provide a deeper level of insight compared to a one-time survey.
Cross-reference with a soil test: You can send your soil to a professional lab or see if your local extension office can test your soil for you. You can get more immediate results for pH, nitrogen, potassium, and phosphors levels with some at home tests. For example, this pack of 10 pH, NPK test kit or try a digital soil test kit. soil pH meter.
A word of caution: don't over-adjust: It’s important to understand the fine balance between amending the soil properly and overloading the soil in excess and creating other problems. Follow directions on the soil amendments that you purchase, and err on the side of moderation rather than trying to over-compensate.
Take an Ecosystem Approach to Soil Health
It’s important not to see a single isolated plant as an over-arching indicator of your entire garden. Instead, we need to view soil health with an understanding that our backyard gardens are ecosystems, with different elements from bacteria and fungi to trees and animals all interplay with each other.
With this perspective, we can see how all of these characters come together to tell a story of our soil’s healths and needs.
Here’s how you can apply an ecosystem approach to soil health:
Biodiversity is Top Priority: Instead of monocropping, biodiversity within the soil support proper nutrient cycling and can boost organic matter.
No-Till Methods Improve Soil Health: Remember that the soil is alive with a whole world of bacteria, fungi, and invertebrates that contribute to soil health. Tilling is kind of like Godzilla walking across your town - the environment would get totally torn up. Instead, no-till methods help keep the soil microbiome intact, giving it an opportunity to grow and expand with the effect of healthier soil along the way.
Organic Matter: Organic matter offers a solution to many soil issues. It can improve soil structure, add nutrients, and support moisture retention. Start looking for ways to incorporate compost, mulch, and cover crops in your garden to help boost your soil health.
Climate Resilience with Indicator Plants
Something interesting to think about it how the wild plants that grow in your lawn and garden can support you to create adjustments that will help your yard to be more resilient to climate change.
For example, learning that your soil is dry and remedying it can help your garden to survive periods of drought, or improving soil drainage can help your yard to withstand heavy rain events (Enhancing climate change resilience in agricultural crops, 2023).
Here's another way to think about it. In the white paper “The Concept and Future Prospects of Soil Health,” authors from Cornell University and the Technical University of Munich share a different perspective to soil health.
They explore how the notion of “soil security relates to the need for access to soil ecosystem services to be on the same level as other human rights…similar to water and air.”
This means that soil security is interconnected with food security. As it happens, soil security is also intertwined with carbon sequestration. As a result, we can see tending to the soil as necessary in the fight for a sustainable future and habitable planet.
The authors go on to make the connection between regenerative practices and soil health - like organic inputs, organic matter, no-till practices, cover crops, and plant diversity. These sustainable practices contribute to the health of not just the soil, but to the entire ecosystem as well.
When you pay attention to indicator plants, you can not only improve soil health but also fortify your gardens against the increasing threats posed by climate change.
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