What color is your garden soil? Does it make a difference?
Yes! Some of the factors that alter the color of soil include:
- Mineral content.
- Degree of weathering.
- Presence of organic matter and humus.
All of these considerations are very important to the health of your garden plants.
Dark Brown to Black Soils
This color range is associated with rich soils, and with good reason. Rich dark brown or black soils typically contain ample amounts of humus and organic matter. The darker the color, the more decomposed the organic matter is—in other words, a greater percentage of organic matter has finished the process of breaking down into humus.
Also, very dark soils generally contain sodium, as sodium causes organic matter and humus to disperse more evenly throughout the soil.
But truly black soils can also indicate trouble in the form of complete saturation and high levels of anaerobic bacteria. Fortunately, there is no mistaking this type of black with the rich black of healthy soils. Unhealthy black soils look and smell disgusting—they are basically vats of anaerobic rot in the making.
Red, Orange, Yellow, and Tan Soils
Reddish and red-brown soils typically indicate high levels of hematite, an iron oxide. The depth of the red is a good indicator of the efficiency with which the soil drains. Bright reds indicate excellent drainage and infrequent saturation. Pale reds suggest that nutrients have been leached out of the soil due to a lack of organic matter.
Orange soils are seen when iron has been precipitated out of water. Thus, an orange color suggests that the soil is periodically waterlogged. Or if your soil was previously some other color and has suddenly turned orange for the first time, it could indicate that the problem is with excess iron in your water supply.
Yellow soils indicate the presence of goetithe, another iron oxide mineral. As with red soils, the brighter the color the better the drainage. As also mentioned with reds, pale yellow soils have been leached and would benefit from the addition of some organic matter to retain nutrients.
Note that intermediate tan colors are formed when organic matter is added to soils containing iron oxide.
Gray to Blue-Gray and Green-Gray Soils
What happens if a red or yellow soil is submerged for an extended period of time? The aerobic bacteria normally present in the soil eventually run out of oxygen and go dormant, leaving the field open for anaerobic bacteria. Anaerobic bacteria use up a great deal of iron in their metabolism process, altering ferric iron to ferrous iron in the process. Ferrous iron has no color; thus as the anaerobic bacteria feast and multiply, the color disappears from the soil. Meanwhile, with water displacing the oxygen in the soil, the iron compounds that form the mineral element of the soil stop oxidizing and producing rust colors.
Grayish soils, therefore, are found in areas with high levels of both moisture and iron. If a gray soil has a bluish or greenish cast, that may indicate the presence of sulfur. A mottled gray, as opposed to a uniform gray or blue-gray, suggests that the soil is waterlogged at times and fairly dry at other times.
But in any case, gray soils are definitely a cause for concern, as they indicate a poor drainage situation and frequent saturation.
A layer of white between the topsoil and the subsoil usually contains a high percentage of sand. Leaching is the cause of the color (or lack thereof). Plenty of organic matter will be needed to correct this situation.
White coloring in the subsoil is typically due to the presence of calcium carbonate. However, white soil containing calcium carbonate may be seen at the surface of the ground if exposed by erosion. This type of soil typically occurs only in desert areas, as regular rains prevent calcium from accumulating.
Using This Information
Soil color can be a useful tool for evaluating a potential garden site. If you have a healthy dark brown or black soil, great! However, a bright red, yellow, or tan soil will work, as well.
Avoid pale and gray soils whenever possible, as these signal serious drainage problems that will have to be overcome. Likewise, white soils will require a great deal of effort to improve. If you don’t have much choice on soil quality, you may want to consider gardening with raised beds and purchasing a good mixture of soil and peat moss to be amended with homemade compost as necessary.
When gardening on red, yellow, and tan soils, you should not have too much trouble with drainage. However, you will want to raise the levels of organic matter in your soil. This can be done with a combination of mulch, compost, and patience.