Garden Guy: Soil amendments, part 1
My last two articles have been about bed preparation. Proper soil preparation provides the right soil structure (soil texture) and soil chemistry (soil fertility) for the plants grown in it to thrive. Texture and fertility can differ among plants.
Good garden soil contains 30 to 50% sand, 30 to 50% silt, 20 to 30% clay, and 5 to 10% organic matter. The balance is pore space for water and air. Mineral is composed of sand, silt, and clay. One teaspoon of healthy soil contains a billion invisible bacteria, several yards of invisible fungal hyphae, several thousand protozoa, arthropods, and a few dozen nematodes (collectively soil critters).
Good soil structure with the proper balance of organic matter provides drought protection by holding moisture. It helps sandy soil hold more moisture by reducing pore space and improves aeration in soils with too much silt and clay by providing more pore space. It stops erosion by binding soil particles together.
Good soil has humus, the end product of composting organic matter, which provides and holds nutrients readily available for use by plants. As weather gets warmer and more nutrients are needed because of plant growth, soil critters work harder to make more humus.
The characteristics of most of our local soils are that they are clay, which generally means that they do not drain well and are lacking in organic matter. This means that they do not have much fertility. Vegetables require lots of organic matter and prefer a loamy soil. Xeric plants largely need very lean soil with little organic matter and lots of grit. Others need more balance between loamy and lean.
Most plants prefer a slightly acid to neutral pH (7) while others grow better in alkaline soil. Both texture and fertility can be changed with the proper amendments although significant long-term changes in pH requires ongoing attention and can be costly in time, labor, and money.
To learn the composition of your soil, you should have a soil test done. To find out all you need to know about soil testing, Google “soil testing” and you will find abundant information. There is a soil testing lab in Amarillo that can help you out.
Organic material feeds the soil and encourages microorganisms (soil critters) in the soil to flourish. The work of these critters produces nutrients and change the chemical structure such that some present but unavailable elements are allowed to be taken up by plants. In addition to improving both sandy and clay soils, organic matter also lowers the pH in alkaline soils and raises it in acidic soils moving the pH toward neutral.
When you know the makeup of your soil and what kind of gardens and plants you intend to have, you are ready to determine the amendments that will be appropriate for each distinct area. This necessitates that your plans should group plants with like needs together so that the soil is appropriate for all that are growing there. Next week I will discuss these amendments.
This article originally appeared on Amarillo Globe-News: Garden Guy: Soil amendments, part 1
