"Between winter and spring," my husband Ward likes to say, "we have a season called 'mud'." The driveway becomes a quagmire you can get the car stuck in, wheels spinning uselessly. Before we put big, flat stones in the path to our front door, in this season you could lose a shoe trying to walk across the yard. Even with those stones, and even removing footgear at the door, we bring a lot of the yard into the house....
Soil is a mixture of decomposed vegetation (humus) with mineral particles produced by ages of rock erosion: clay, silt, and sand. In a quarter-teaspoon, there are about five thousand grains of sand. The same measure holds five million particles of silt, or ninety million of clay.
When the ground has thoroughly thawed, take a small handful of your soil, put it in a jar of water and shake it well: the sand will precipitate in 40 seconds; the silt in half an hour, and the clay, 24 hours. Measuring the depth each time, and subtracting the previous level, will give you the relative proportions of these three components in your soil.
In mud season, the surface of the soil has thawed, but a frozen layer remains underneath, preventing drainage. When the saturated dirt is disturbed, clay rises to the top. Clay is sticky.
Once I tried to garden in heavy clay; the sandy extreme I have now is easier. But my soil would benefit from more clay. To improve moisture retention, I add a lot of compost. However clay also has unique chemical properties: it retains fertilizer in the soil, forms useful bonds with other structural elements of the soil, and adds minerals.
You can buy calcined montmorillonite clay, which has been fired in special kilns into a form that's hard and stable but highly porous. Usually the product is little, terra-cotta colored pieces the size of rice grains; it not only retains moisture, but because the particle size is big, also drains well (unlike raw clay). It's used to improve soil structure in compacted athletic fields, as a component of a soilless seed-starting medium, and in potting alpine plants and bonsai. I'd like to dig some in around my roses. But it doesn't have the chemical advantages of raw clay.
So I look at the mud in the driveway, and tell myself to be grateful I do have some clay.
© Copyright 2003 Catherine Holmes Clark
|For more information
Mud Season in VermontGuidelines for Hiking in Mud Season on the Vermont Living site, focuses on the problems of dirt roads.
Factors affecting metal uptake in soils A discussion by Myung Chae Jung, PhD, of the Department of Earth Resources & Environmental Geotechnics Engineering, Semyung University, Korea, gives a few examples of the chemical activity of clay in soil. (There are others, outside the scope of his paper.)
Soil and Minerals a summary of the role of clay in colloidal combination with humus.
Calcined montmorillonite clay products: