“The assemblies of the clays are like those hedge mazes and forests in which fairy-tale children become lost, like those places where the old woman is met and where treasures are won. The landscape of the clays is like the wall of the stomach, or the tree of the capillaries, or the intricate folds of the womb. It is the honeycomb of matter, whose activity is to receive, contain, enfold, and give birth.” ~ William Bryant Logan, “Dirt: The Ecstatic Skin of the Earth,” 1995
Wow! Who knew a description of clay soils could be so poetic? Then again, that’s why William Bryant Logan’s book is my favorite book about soil. Logan argues that, far from being inert, clay is a living thing and may have “spawned all the creatures now inhabiting the earth.” Indeed, the Hebrew word for “red clay” is adam, so, Logan says, “perhaps our ultimate ancestor really was (A)dam.”
Fascinating! Logan makes me feel a whole lot better about the preponderance of clay in my yard, the kind of soil local folks call “black sticky.” East Medford, where I live, is infamous for its clay soils, although when I typed in my address on SoilWeb, I learned that the majority of soil in my “map unit” (44c) is composed of between 20-27.5 percent clay when the soil is dug at least 6-12 inches from the surface. According to SoilWeb data, only 2 percent of the soils within my area are composed of 60+ percent clay. This wide variation is due to the presence of an alluvial fan, a cone-shaped deposit of sediment from an underground stream making its way to Bear Creek about 1 mile downhill from my property.
I used an adaptation of the Jar Test, recommended by the OSU Extension Service, to analyze a soil sample from a raised berm in my front yard. I dug about 8 inches down, past the bark mulch, to collect the soil sample, and then mixed 1/2 cup of the soil with 3 cups tepid water in a glass container. I stirred the mixture thoroughly and let it stand overnight, and then I measured the proportion of sand that made up the bottom layer, silt that made up the middle layer, and clay that made up the top layer.
As the picture shows, the clay layer comprised 90 percent (4 1/2 inches) of the total depth of the three layers (5 inches). The sand and silt layers comprised only 10 percent (1/2 inch) of the total depth. The sand and silt layers were about equal, measuring about 1/4 inch each. I’ll take additional samples from other parts of my yard to get an overall picture of the texture of soils on my property.
I also conducted the Hand Method with a handful of the moist, freshly dug soil from my front yard berm. I was easily able to work the soil into a ribbon that measured about 6 inches long. According to OSU soil science professor, James Cassidy, clay content equals approximately 10 percent for every inch of ribbon, which means that my soil content is at least 60 percent clay. This confirms the SoilWeb data. I think I could have worked the handful of soil into a thinner ribbon that would have measured about 8-9 inches, which would support the results of my Jar Test. Regardless, I have confirmed that I have a whole lotta clay in the soil on my property!
For a more detailed analysis of the soil in my yard, I can send samples to the OSU Crop and Soil Science Central Analytical Laboratory. The lab can analyze just the texture of my soil or conduct a comprehensive soil health assessment. The lab even provides instructions on how to read the results of your soil analysis.
In the meantime, which plants are more likely to thrive in clay-based soil? As it turns out, quite a few plants have adapted the ability to grow well with a lower amount of oxygen in the soil. Flowers that do well in clay soils include asters, goldenrod, black-eyed Susan, Russian sage, daylily, yarrow, canna, coreopsis and a variety of ornamental grasses.
The University of Minnesota Extension Service provides a comprehensive list of trees and shrubs for clay soils.
Shallow-rooted vegetables tolerate and may even benefit from the the water retention of clay soils. Such vegetables include those from the Brassica family – broccoli, Brussels sprouts, cabbage, cauliflower and kale – in addition to beans and peas. Root crops, such as potatoes and daikon radish, do a great job of breaking up clay soils. In fact, according to Master Gardener Scott Goode, planting daikon radish in clay soils will loosen the soil to as much as six feet below the surface. Daikon also releases sugars and other nutrients into the clay, which feeds microorganisms that grow in the radish plant’s extensive root system. “When left to decompose in the soil, this remarkable volume of biomass suffuses the clay with organic material. This can transform a clay soil into a rich, deep organic soil,” Goode says.
What are other ways I can improve the clay soil in my yard? Goode recommends three strategies:
- Simply keeping a clay soil well mulched will keep it from drying out and forming deep cracks. The mulch will encourage earthworms and other soil organisms to build habitat near the surface of the soil, allowing rain to soak into the soil rather than compacting the surface on impact and flowing away as runoff.
- The difficulties associated with clay soil, such as stickiness and cracking, are resolved with the addition of organic material. The fastest way to add organic material to a clay is to work humic acid into the soil. It is impossible to add too much humic acid to a soil since it will not change the pH (acidity) of the soil. Organic material can also be added with high-quality compost.
- Clay soils respond very well to lasagna style composting. If you build the pile in the fall and let it work over winter, you will usually see a noticeable difference in the spring.
Along with strategies to successfully garden in the clay soil of my yard, I have great respect for my “black sticky” and all types of soil. As environmental activist and poet Wendell Berry wrote, “Soil is the great connector of lives, the source and destination of all. It is the healer and restorer and resurrector, by which disease passes into health, age into youth, death into life. Without proper care for it we have no community, because without proper care for it we can have no life.”