- Fertilizers are used to add nutrients to the soil. Plants require varying amounts of around 16 basic nutrients. Carbon, hydrogen and oxygen are available from the air and water. The three most important nutrients gleaned from the soil are nitrogen, phosphorous and potassium. Plants use large amounts of these three nutrients, and all fertilizers contain amounts of one or more of these nutrients. Along with magnesium, sulfur and calcium, these are called macro nutrients. Plants also need varying amounts of smaller nutrients, called micro nutrients. The most important of these are manganese, boron, chlorine, zinc, iron, copper and molybdenum.
- Fertilizers come in two basic types, organic and chemical. Organic fertilizers are entirely natural in origin, and may come from a wide varieties of sources such as various animal manures, seaweed, fish emulsions, blood and bone meals and others. These types contain nutrients in forms which are less readily available for immediate use, but tend to release their nutrients more slowly over longer periods. Organic fertilizers also tend to contain more of the other nutrients needed by plants besides the basic "big three" of nitrogen, phosphorous and potassium. Chemical fertilizers are entirely man-made. They contain nutrients in forms readily usable by plants and are quickly absorbed but do not provide sustained long-term feeding. Both types come in dry and liquid forms, in many different nutrient ratios. Fertilizers will be labeled with a series of three numbers, for example, 10-15-20. These numbers represent the relative percentages of the total of the fertilizer of the three basic nutrients, nitrogen, phosphorous and potassium, respectively. Therefore, in the previous example, the fertilizer would contain 10 percent nitrogen, 15 percent phosphorous and 20 percent potassium, the remaining portion being other nutrients (indicated on the label) or inert ingredients.
- Fertilizers high in nitrogen are good for lawns, and vegetables grown primarily for their leaves or stalks like spinach, lettuces, cabbages and others. Trees and vegetables grown primarily for their fruits or seeds benefit from higher concentrations of phosphorous and potassium. Tomatoes, for example, may produce very little fruit and an abundance of leafy growth if fertilized only with a high-nitrogen fertilizer and not enough phosphorous and potassium. Almost any garden center will carry many different types of fertilizers. Check the labels for suitability for your specific needs.
- Soil amendments are used for improving soil quality, not soil fertility. Soil quality is important because a good soil texture will improve plant growth by promoting availability of nutrients, water retention, drainage and root growth. An ideal soil has balanced qualities of high organic content, a slightly acid pH of 6.0 to 6.8, good drainage, the ability to hold some water, the ability to resist compaction and good nutrient-holding capacity. Various soil amendments are applied to soils lacking in one or more of these qualities to improve the soil.
- Many different soil amendments may be applied to soil, depending on the desired effect. Compost is most often applied to improve texture and raise organic content. Lime may be added to acidic soils to raise pH levels, and sulfur to alkaline soils to lower pH. Peat moss is a very common soil amendment as it can loosen heavy soils, such as those high in clay content, but add body to very sandy soils. It also adds organic material to the soil. Peat moss also has a unique ability to hold up to 20 times its own weight in water, which helps slow moisture loss. Wood chips, grass clippings, straw and ashes are other common organic soil amendments. Inorganic amendments are also sometimes used. Some common types are perlite and vermiculite, also widely used in seed-starting mixtures and man-made potting soils. Other inorganic soil amendments are sometimes used, but generally organic types are favored by most growers as they have more advantages. Many organic soil amendments also contain small amounts of nutrients, allowing them to act as supplemental fertilizers.
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