Using Weeds to Read the Soil: Some Basic Concepts to Get Started

Weeds are becoming a more and more appreciated component of gardening. We have been reintroduced to eating the weeds, with things like dandelion leaves becoming a niche crop. Also, we are encouraging plants that, up until recently, were viewed as weeds (dynamic accumulators like comfrey and pioneering legumes) to revitalize our soils. And, many gardeners are once again celebrating weeds as a means of reading the soil.

Geoff Lawton says weeds are not the problem but rather symptoms of glitches within the soil. In other words, weeds have arrived because the soil has some sort of deficiency or condition that both allows them to thrive and prompts nature to repair systemic damage. Nature will move towards a permanent, stable system, and weeds are part of that process, especially in troubled landscapes.

With each problem, there are particular weeds that characteristically appear, and if we learn to read these weeds, we can assess unfamiliar landscapes and recognize the sources of troubles within our own systems. Then, we can begin to speed the soil’s recovery into something more stable, and in the meantime, we can cultivate appropriate plants to aid this process and provide production, as well as utilize weeds that are already present.

While each landscape, soil type, and climate has its own particular set of pioneering plants, there are some basic ideas that can help us begin to understand more how to use the weeds to read the soil. From there, we can research and make more practical and informed decisions as to how we might move our projects in positive directions.

The Root Systems

Thistle (Crispin Semmens)
Thistle (Crispin Semmens)

The root systems of weeds can tell us a great deal about soil conditions. For example, weeds that have deep taproots, such as dandelions and burdock, generally indicate soils that are compacted, preventing plants with lesser roots from taking hold. These taproots break up the soils and eventually, as they decompose, create pathways for water, nutrients, and weaker roots systems. On the other hand, weeds that have spreading, hairnet root systems or clumping grasses are likely there because soils are loose and erosive.

So, when there is an abundance of weeds, we can start by noticing their root systems as these might indicate soil conditions that we can either address with rehabilitative gardening techniques or by choosing appropriate plants to grow in the conditions. This can also lead us into identifying the weeds that are present and learning what other things they might be telling us.

The pH Balance

Just like crops, some weeds thrive in different levels of acidity and alkalinity. We wouldn’t plant blueberries in a soil that we know is alkaline because we recognize that blueberries are particular to acidic soils. Well, certain weeds—plantain, hawkweeds, sheep sorrel—could help to indicate more acidic areas, whereas others—goosefoot, true chamomile—signal the likelihood of alkaline soils.

A shrewd gardener would use these signals to help with choosing what crops he or she might try to cultivate in an area. If the soil is acidic, berries might be a great choice, but if the soil is alkaline, different cruciferous vegetables are likely a better option. Similarly, noting these bits of information can be guidance for what not to plant in an area, something that might prevent wasting time and resources.

The Soil Types/Conditions

Elastic Grass (Harry Rose)
Elastic Grass (Harry Rose)

The ability to recognize the weeds we are looking at can also give us an assessment of the type of soil it is growing in and the conditions of that soil. If it’s sandy, we might see sandbur, cornflower, or dog fennel, but a heavy clay soil is more likely to yield wild garlic, plantain, and creeping buttercup. Wet soils—cattails, sedge, marsh mallow—will have different weeds than dry soils—potato vine, Virginia pepperweed.

Again, this can aid cultivators greatly by knowing whether to plant crops that thrive in sandy soils over clays or wet soils over dry. Recognizing these needs before investing the time and money needed for a garden can mean the difference between low-maintenance success and hard-working struggle. Taking a moment to familiarize with the weeds common to a place is just a good idea.

The Nutrient Profile

When we stop looking at weeds as only pests and recognize they are plants, we realize that, like all plants, they have certain nutritional needs and outputs. The existence of certain weeds can provide clues to what the soil nutrients is like. Chicory, purslane, and lamb’s quarter (all edible) indicate rich soils, but sheep’s sorrel and broom sedge might mean the opposite. Thistle could mean deficiencies in iron and copper, or the growth of ferns and blade grasses will show up in places that have been burned, indicating a lack of available phosphorus.

Learning certain sure indicators of nutrient abundance or absence can lead growers as to which soil amendments they might need to make, as well as which crops—one’s that like similar nutrient profiles—they might want to plant. This could help in moving the soil slowly and deliberately back into a more balanced system with more biodiversity.

The Weed Community

Weed Mosaic (Paw Paw)
Weed Mosaic (Paw Paw)

In the end, it’s important to remember that no one weed necessarily provides all the information we need to assess soil, but using the community of weeds growing in an area will provide a more complete view of what the soil type and conditions are, as well as what sort of issues need to be addressed or considered in developing the land. Identifying the prominent plants in a space and where the meaning behind each weed overlaps could provide reasonably accurate results.

The unfortunate thing is that different climates and locations have different weeds and often different names for the same weeds, so this might mean buckling down for some research before being able to read the weeds well. Luckily, there are plenty of books to reference, as well as local experts and online sources. The point is that learning what weeds we are looking at and what they are saying is an effort most certainly worthwhile.

5 Books to Help Getting Started with Reading the Weeds:

Weeds and Why They Grow by Jay L. McCaman

Weeds and What They Tell Us by Ehrenfried E. Pfeiffer

Weeds: Guardians of the Soil by Joseph A. Cocannouer

Weeds: An Earth-Friendly Guide to Their Identification, Use and Control by John Walker

Insect, Disease & Weed I.D. Guide: Find-It-Fast Organic Solution for Your Garden by Deborah L. Martin

Feature Header Image: Dandelions (Chris Alban Hansen)

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6 thoughts on “Using Weeds to Read the Soil: Some Basic Concepts to Get Started

  1. I recognize all these from living up north, but here in S Fl we have few or none, and sugar sand replaces soil. Would love to import our soil from CT!!!

  2. I really appreciate weeds for being food for my animals. Stinging nettle, dandelion, plantain, lambwort, burdock, sorrel – they all are fed to my beast – ducks, geese, chicks and goat. I only object to poisonous ones but not so much that I would use chemicals on them.

  3. What about those three leaf clover weeds with the little yellow or white flowers (Oxalis)? I found them a nuisance, until my son said, “Mom you can eat them!” Sure enough, the leaves, flowers and unripe fruits are edible, with a mild lemon-sour flavor – that’s were it gets the name sour grass. Edible gardeners use it as a salad green or add them to soups, sauces or as a seasoning.

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