Types of Soil

Plants animals and humans share a common need for food, water, air and sunlight to grow and stay healthy.

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In the plant world, soil serves as the primary transfer medium.

It's no understatement to suggest that healthy soil represents the foundation for a healthy garden. Given that fact, organic gardeners commonly take notice of two types of soil information, soil types and soil properties, to insure their soil is at its medium best.

Most beginner's guides to soil remind us that soil consists of both organic and inorganic (living and non-living) elements. Bacteria, viruses, yeast and other living organisms constitute the living part of the soil. There may be more of these organisms in your soil than you think. One estimate suggests that as many as 3,000,000 to 500,000,000 bacteria could exist in an area the size of a paper clip.

While plant growth can be harmed by bacteria or any other living organism, the vast majority of these organisms, at least under optimum soil conditions, benefit plant growth by breaking down nutrients making them amenable food forms for plants. Organic gardening builds on the idea that healthy gardens, those requiring the least amount of chemical nutrients, start with high levels of organic materials. Composting and the addition of nature produced nutrients serve as the primary tools for organic gardeners looking to improve on their soil's fertility.

Soils can further be differentiated based on the characteristics of their non-living elements. Most inorganic soil substances are mineral based, important because they help determine soil density. Depending on which reference one reads, two or three main soil types are commonly discussed.

• Clay Soil - small sized non-living particles creating highly dense soil
• Silt - medium sized non-living particles creating to medium density soil
• Sandy Soil - large sized non-living particles creating low density soil

Organic gardeners take note of their soil types primarily because each type differs in its ability to transfer food and water to the plant's root system. For example, the relatively high density of clay soil creates it own dilemmas for gardeners. In times of drought, clay soil's ability to retain water might be beneficial. However, on other water abundant occasions, plant roots unaccustomed to water, might have a difficult time staying healthy. Plants, like humans can drown. Additionally, because of its density, clay soil retains nutrients better than its counterparts, a good characteristic if plants are hungry, a less than perfect characteristic in instances of nutrient over exposure.

The exact opposite set of circumstances applies to soil at the other end of the spectrum, sandy soil. The relatively large size of its non-living particles means that both water and nutrients drain away more quickly from plants. Good for plants during the rainy season and perhaps harmful to plants during drought occasions.

Since most plants thrive best in an environment that balances water and nutrient retention, most, if not all organic gardening specialists recommend mixing humus (decayed organic matter such as tree bark or peat moss) or compost into the soil. Soil mixing creates loam, the goldilocks category of soil, not too dense, not too porous. Having the ability to balance plant water and nutrient requirements, loam's the organic gardener's number one choice as a growing medium for plants.

Soil tests also provide gardeners with two additional soil facts or properties, pH level and nutrient content. The pH scale, is a chemical scale that measures the relative acidity or alkalinity of the soil. The scale is set between 0-14 with 0 meaning totally acidic (sour soil) to 14 meaning totally alkaline (sweet soil). A 7 means the soil is neutral. Of course the majority of soil falls somewhere in between. Knowing your soil's pH level helps during the garden planning period because different types of flowers and vegetables are suited to different types of soil. For example, many garden references place common garden vegetables in the 6-7.5 pH level.

Adequate pH level does not automatically ensure healthy plant growth in your garden. Because plants require proper nutrition to thrive, soil nutrient levels are also important. Although there are 16 nutrients that plants need, nitrogen, phosphorus and potassium commonly receive the most attention. A good rule of thumb for remembering the value of each nutrient says that nitrogen helps leaves and stems, phosphorus contributes to root development and potassium encourages more productive plant flowering.

Organic remedies for nutrient deficient soils abound. Soils with a low pH level (acidic between 0-6.9) can be treated with lime. Sulfur can be added to soils that are too alkaline (between 7.1-14). The necessary amount to apply depends on both your soil type and pH level. Organic fertilizers, including compost and manure, can be applied to the soil during the off season to help build back some of the nutrients lost during the growing season.

Gardeners should take note that organic choices such as these are time sensitive. It takes at least three weeks before applied organic material such as compost and manure disperse their nutrients throughout the soil.

© 2000-2006. Patricia A. Michaels