Dreading the ocean of oxalis taking over your lettuce bed? How about that crabgrass creeping through the potato patch? You should really get out there and pull those invaders, but before you do, give yourself a break and dive into the weird world of weed analysis.
What grows on its own is a surprisingly reliable indicator of everything from soil pH to moisture content to the deficit of particular minerals in your soil. By learning to read these natural indicators, you’ll have a better idea of what crops will thrive on your plot of land (those that will grow like a weed!) and what sorts of remedies are required to make struggling crops healthier and more productive.
If your weeds are trying to tell you that your pH is very low (acidic), you may need to add lime to boost your soil into the range preferred by most vegetables — or you could plant blueberries, which require acidic soil to thrive. If your weeds indicate heavy, poorly drained clay, you may need to invest in building raised beds and importing free-draining topsoil — or you could plant a bog garden. For a deeper dive into the subject, check out Ehrenfried Pfeiffer’s Weeds and What They Tell Us, a classic text on biodynamic agriculture.
- Clover High in magnesium, low in nitrogen
- Sedge Poor drainage
- Garlic mustard Fertile, alkaline soil (high pH)
- Plantain High in nitrogen, rich in organic matter
- Sorrel Acidic soil (low pH), low in calcium and nitrogen
- Dandelion High in potassium, low in calcium
- Chicory Alkaline soil (high pH)
- Crabgrass High in potassium, low in calcium
- Pennyroyal Excessively wet
- Thistle Low in copper and iron
- Mullein Low fertility, excessively dry
- Horsetail Low in calcium, poorly drained
- Bindweed Compacted clay soil
- Oxalis Fertile, acidic soil (low pH), low in calcium
- Yellow dock Compacted clay soil
- Knapweed High in potassium, low in phosphorus
- Moss Low fertility, excessively wet, very shady
- Yarrow Low in potassium, sandy and dry
- Bracken Fern Acidic (low pH), low in phosphorus
- Pigweed Low in manganese and phosphorus
Correction: A previous version of this article incorrectly stated that Oxalis is an indicator of high pH. We apologize for the error.