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IntroductionGardening Equipment: Tools for getting started Soil Preparation Composting Fertilization Use of Pesticides in the home landscape Organic Gardening Irrigation |
Fertilizing Basics
Fertilizing gardens and landscapes is important to maintain healthy growth and acceptable appearance.
Under natural forest conditions, the annual decomposition of leaves, needles and twigs provide a fresh resource of minerals for
plants to use. Landscapes usually do not have this nutrient source and are in need of additional minerals since landscape debris is routinely hauled away. There is an endless supply of products available to fertilize your plants. It is important to understand basic plant nutrition and fertilizer application principles in order to meet garden fertilizer needs.
Sixteen chemical elements are known to be important to a plant's growth and survival. The first of these are carbon (C), hydrogen (H) and oxygen (O), which plants acquire in sufficient quantities from the air and water. The other 13 mineral nutrients are acquired by plant roots, which absorb soil minerals dissolved in water.
The primary macronutrients are nitrogen (N), phosphorus (P), and potassium (K). These major nutrients usually are lacking from the soil first because plants use large amounts for their growth and survival. Expectations are that some amount of these three nutrients will be needed in the garden every year. Determination of the amount to apply can be made using historical need recommendations found in many garden publications, or using the results of a soil test. Your local count extension agent can provide instructions for taking a soil sample. The secondary macronutrients are calcium (Ca), magnesium (Mg, and sulfur (S). Fertilization with these nutrients is not always needed. Micronutrients are nutrients needed needed in only very small quantities . The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). In the high pH soils of southern Idaho, levels of S, Fe, Zn and Mn are often deficient. Once needs are determined, calculating fertilizer application amounts can still be a daunting task for the novice gardener. First, nutrient content of the fertilizer must be determined. This information is found on the fertilizer package, usually in the form of three grade numbers. For example, if the fertilizer grade is listed as 10-10-5, the fertilizer contains 10% nitrogen (first number), 10 percent phosphorus (second number), and 5% potassium. If there is a fourth number, it is the percentage of sulfur.The final information that must be accounted for is the land area to be fertilized. Once all of these factors are known, standard formulas can be used to determine the amount of any fertilizer product to apply. The web publications listed below contain variations of these formulas that will aid in the final calculations. Organic materials are available that can take the place of inorganic fertilizers in the garden. Common forms include blood meal, bone meal, cottonseed meal, sewage sludge, composts, and manures. These fertilizers are usually relatively low in the percentage of nutrient content compared with conventional formulations and sometimes applications of relatively large quantities are needed. Especially when purchased pre-packaged, they can be more expensive than inorganic fertilizers. Colorado State University has published a great discussion on organic fertilizers, found at: http://cmg.colostate.edu/gardennotes/234.pdf Fertilizing in a landscape is complicated by the fact that different plants have different nutrient requirements. For instance, a lawn uses high amounts of nitrogen while trees generally need very little nitrogen, especially in the late summer and fall when applications may induce new growth which may result in winter cold injury. For a discussion of meeting fertility needs of individual vegetable crops, see the following New Mexico State University publication: http://www.cahe.nmsu.edu/pubs/_h/H-120.pdf. Managing fertility on other types of plants in Idaho is described in these University of Idaho on-line publications: Fertilizing Landscape Trees: http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS1068.pdf Growing Raspberries and Blackberries: http://www.cals.uidaho.edu/edComm/pdf/BUL/BUL0812.pdf Growing Blueberries (northern Idaho): http://www.cals.uidaho.edu/edComm/pdf/BUL/BUL0815.pdf Growing Strawberries: http://www.cals.uidaho.edu/edComm/pdf/BUL/BUL0810.pdf Backyard Grapes: http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS0790.pdf Lawns (northern Idaho): http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS0911.pdf Lawns (southern Idaho): http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS0846.pdf Beans and Peas: http://www.cals.uidaho.edu/edComm/pdf/PNW/PNW0495.pdf Potato Production in the Home Garden: http://www.cals.uidaho.edu/edComm/pdf/CIS/CIS1000.pdf By accessing the University of Idaho Resources for Idaho catalog, production and fertilization guides for many additional garden plants can be purchased. Peruse the list at: http://www.cals.uidaho.edu/edComm/catalog.asp?category1=Gardening Sometimes adding materials to the soil may be beneficial in certain geographical areas while detrimental in other areas. For example, addition of wood ashes and lime make acidic soils more alkaline (higher pH). Consequently, these may be good amendments for northern Idaho's soils, but not for southern Idaho's calcareous, alkaline (high in lime) soils. There are other excellent fertilizer guides on-line. These include: A general discussion about fertilizing a home garden is found in the bulletin, Fertilizing Gardens, published by University of Idaho. A good publication by Oregon State University that provides information on interpreting soil test results, determining fertilizer needs, and calculating application amounts, at: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19239/ec1503.pdf 
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The
required mineral nutrients are divided into two groups:
