Home > Seed Tips > Soil


What type of soil does your garden have? Grab and handful of moist soil-does it stick together in a muddy ball? Does it slide through your fingers? Good soil should form a loose, crumbly ball in your hand. Check the soil in several spots in your garden; soil type can vary from area to area. In areas with new houses, rich topsoil may have been removed during construction, leaving only the hardpan underneath.

        Soil is composed of organic and inorganic materials. The organic materials create spaces that allow air and water to penetrate to the plant roots.

Soil Types

There are three main soil types:

1. Clay  "(Heavy Soil")
        Clay soil is approximately 60 percent clay, 20 percent silt and 20 percent sand. If clay soil is squeezed when wet it will squish through your fingers. Clay is composed of microscopic mineral particles that fit together closely and do not allow much room for air and water. Clay soils can contain the highest density of minerals. They drain very slowly, are easily compacted and are the last to warm in spring. Clay soil will typically absorb water at a rate of inch per hour. There are a few plants that prefer a clay soil but if you prefer to grow a wider variety of plants you can amend the soil with some of the organic materials listed below. These materials should be well incorporated into the soil, not just placed on the surface.

2. Sandy
        Sandy soil is defined as soil that is 60 percent sand, 20 percent silt and 20 percent clay. Sandy soil will crumble and fall apart if squeezed when moist. Sand is composed of large, round rock particles with spaces between particles, therefore there is more room for air and water. It drains well and warms quickly, however the nutrient density is low due to leaching. Plants planted in sandy soil need more water than those in other soils. Sandy soil can be amended with some of the organic amendments listed below. These materials should be well incorporated into the soil, not just placed on the surface. Sandy soil absorbs water at a rate of 2 inches per hour

3. Loam
        Loam is the ideal soil for the garden. If squeezed when wet, loam will form a rough, crumbly ball in your hand. It is between 8 and 25% clay mixed with sand and organic materials. It drains slowly enough for nutrient absorption and fast enough for air to penetrate for root growth. If your soil is loam consider yourself lucky and care for it well with infrequent organic amendments. Loamy soil absorbs water at a rate of 2 inches per hour.

Soil Additives

There are two types of soil additives: organic and inorganic.

1. Organic Additives
        Because all organic matter is constantly decaying, all types of soils can benefit from an occasional application of organic matter. These include ground bark, peat moss, sawdust, wood shavings, manure, compost and plant remains. Add 25 to 50 percent of soil volume and mix in thoroughly. Humus is the final result of organic matter decay.

        The result of composting is humus. It improves drainage and aeration, as well as improving water retention in sandy soil. Homemade humus is the best amendment you can give your soil. After any application of homemade compost, be sure to give your soil a little extra nitrogen to compensate for nitrogen loss during the decomposition process. Most commercially sold organic amendments are nitrogen fortified so microorganisms don't steal nitrogen from the plants during the decomposing process. To do this, add 1 pound of ammonium sulfate for every 1 inch layer of organic matter over 100 square feet. Excessive use of organic materials can result in overly acid soil.

2. Inorganic Additives
        Perlite, pumice, vermiculite are common inorganic additives. They are used to increase drainage of clay soils and increase water retention of sandy soils by creating pockets in the soil.

Chemical Additives
        Chemical fertilizers are a temporary solution to a long-term problem. Before applying heavy doses of chemical fertilizer, try to amend your soil for the long term with organic additives, compost and humus. Lime and gypsum are two commonly used chemical additives. Lime raises the pH of overly acid soils. Both lime and gypsum can improve drainage of clay soils. Apply gypsum in high alkaline, high sodium soils; add lime in acid soils. Lime adds calcium, gypsum adds calcium and sulfur.

Soil pH

        The pH range for best plant growth is between 5.5 and 7.5. Acid soil has a pH 6.9 or lower and alkaline soil has a pH 7.1 or higher. Neutral soils are pH 7. The pH affects the solubility, and therefore the availability of minerals in the soil. There are home tests to determine soil pH but a professional soil test will not only tell you the pH rating of your soil but will also tell you the exact amendments you need to apply. Acid soils are usually deficient in phosphorous and alkaline soils usually lack manganese, boron and phosphorus.