Gardener's Guide to the Raised Garden Bed
Garden Soil Types - A Quick Soil PrimerSoil is the top several inches of the earth's crust. Soil is necessary for civilization to exist, as it supports the plant life that sustains forests, plains, agriculture and other habitats. Five basic factors influence the formation of soil, the bedrock, climate, local fauna and flora, topography and the passage of time. The gardener will find three layers of soils underlying their garden, the topsoil, and subsoil and parent material. The parent material is the minerals that originally formed the soil. The subsoil is the intermediate level between topsoil and the parent material and will have some qualities of both. The topsoil is the part that concerns most gardeners.
In the Dirt
On average a soil will contain about twenty-five percent air, forty-five percent mineral matter, twenty-five percent water and about five percent organic matter. These levels can vary according to soil type, location, rainfall and other factors. The average soil will include a number of organisms that live in it. These include earthworms, grubs, fungus, bacteria and plant roots.
Topsoil is the first layer of soil, and is the major concern of the gardener. Topsoil can range from a thin layer over the underlying subsoil, or several inches. Good garden topsoil can contain between two and ten percent organic matter. A good garden soil must have the following qualities:
Good aeration, to allow root penetration and allow oxygen to penetrate the soil
Porous enough to allow drainage, but not so porous as to allow soils to dry quickly
The major effort of the gardener should be to work constantly to improve the topsoil quality and fertility. Fertile, loose topsoil will produce healthy, fast growing plants. Healthy plants will suffer less insect damage, have fewer diseases and produce top quality vegetables with maximum nutrition. Poor management of topsoil can cause them to erode away quickly, exposing the less desirable subsoil.
The gardener will encounter six basic types of soils:
Note, there are other soil types, but these are the most common.
Loam is the ideal type of soil for most types of agriculture. This soil will have about equal quantities of sand, silt and clay. It will also boast a high organic content. A good loam has all the qualities listed above, will warm quickly in the spring, be easy to cultivate and is ideal for the greatest number of plant types. The gardener constantly replenishes the organic, humus content of the soil. The gardener can use his fingers to test loam soil. The soil should be dark in color that is smooth to the feel and have a slightly gritty feel. A ball formed by pressing the soil together should crumble easily.
Clay particles are quite fine and create a tightly packed soil. Clay is high in nutrients and retains water well. It will take clay soils longer to warm in the spring and since these soils have good water retention, they tend to dry out slow. A clay soil will form a ball that does not crumble easily. Damp or wet clay soil is sticky to the touch. It is harder to cultivate, especially when wet as it has a tendency to stick to garden tools. Clay soils will grow good plants, as it is fertile. Improve using mulches, compost or green manure crops to add organic matter. Adding organic matter will also improve drainage.
Silty soils are silky to the touch and will leave a soil stain on the fingers. These soils heat up slowly in the spring. These soils are quite fertile and have excellent water retention. However, because of this trait, they compact easily and sometimes plants have a hard time extracting nutrients from the dense soil structure. Some plant roots will rot in these soils. If better drainage can be achieved, possibly by using raised beds, silt soils can make an excellent garden site. As with other soils, use compost, mulches and green manures to add organic content.
Made up of quartz, silica and other minerals, sandy soils feel gritty to the touch. Sandy soils allow water to drain away quickly and escape by evaporation. They tend to be low in fertility. It will not form a ball when rolled between the hands. Plants have difficulty using any nutrients in the soil, as they drain away quickly. These soils do warm up in the spring quickly and are easy to cultivate. Adding compost, using green manures and mulches can increase the quality of a sandy soil.
Peaty soils are dark and have a spongy, damp feel when compressed. Its high acidic content leads to slower decomposition of plant matter, leading to lower soil fertility. These soils also heat up quickly in the spring and have excellent water retention. Because they tend to stay wet, the gardener should supply some drainage like tiling it or use raised beds. Using lime or wood ashes can raise the ph level. Add compost or manure to increase soil fertility. These soils make excellent garden soils.
Quick Soil Type Test
Pour a trowel full of soil into a glass jar. Fill with water and shake well. Allow this to settle for several hours. In clay and silt soils, the water will remain cloudy. A layer of soil particles will form on the bottom of the jar. In peaty soils, several particles will float on the surface, some will sink to the bottom and the water will remain cloudy. In sandy soils, the water will be clear and a layer of sand will form at the bottom of the jar. A loam soil will leave the water mostly clear. The bottom should have several layers of soil particles on the bottom of the jar.
The ph scale indicates whether a soil is acid, neutral or alkaline. The ph range scale runs from 0 - 14, with soils below 7 classified as acidic and over 7 as alkaline. Most vegetable crops prefer a range between 5.5 and 7.0. The gardener can use a test kit from a garden supply store to test the ph. Use lime, or wood ashes to correct soil that is too acidic. Use aluminum sulfate to correct alkaline soils. Use care using these materials, as it is easy to overcorrect.