Using natural organic fertilizers in the home landscape
By Dawn Pettinelli - UConn Home & Garden Education Center
Featured Article - posted Tue., May. 29, 2012
Interest in natural organic lawn and garden fertilizers has been on the rise in recent years. A visit to the local garden center, farm supply store, or even many big box retailers finds shelves stocked with greensand, bonemeal and other natural organic sources of nutrients. A fertilizer is considered organic if it was produced from once-living or live sources. Examples include cottonseed meal, manure or fish emulsion. By definition, organic amendments contain carbon compounds.
Natural amendments include greensand, rock phosphate and Epsom salts. These are naturally-occurring mined minerals, but since they do not contain carbon compounds, they are not technically organic materials. But enough with the semantics – together, these fertilizers are considered natural organics, as opposed to synthetic fertilizers which have been synthesized or chemically altered by man. One potential problem to beware of when purchasing natural organic fertilizers is that they may be labeled organic, even if some of the constituents are synthetically produced. Urea is a source of nitrogen that is synthetically manufactured, but because it contains carbon, technically it can be labeled as an organic fertilizer.
Natural organic fertilizers have advantages as well as a few disadvantages. Aside from adding nutrients, they often add organic matter to the soil. Organic matter helps soils by increasing water and nutrient retention, improving soil structure and drainage, and by providing food and energy for soil organisms. The nutrients in natural organic fertilizers are usually released slowly, so there is less chance of burning your plants. Also, since they are derived from natural sources, they often contain a wealth of trace elements. Because of their typically low nutrient content, a greater amount of a natural organic fertilizer may need to be applied per square foot of garden or lawn than the more concentrated chemical formulations.
Regardless of their source, plants require at least 16 different nutrient elements to grow and manufacture food through the process of photosynthesis. Nitrogen, phosphorus and potassium are needed in the greatest quantity, and hence considered primary nutrients. Every fertilizer product, natural organic or chemical, will have three numbers on the package which correspond to the percentage of these three nutrients, respectively, contained in that product. For example, a 10-pound bag of 10-10-10 contains 10 percent, or one pound each, of nitrogen, phosphorus and potassium. A 10-pound bag of greensand (0-0-7) contains no nitrogen, no phosphorus, and 0.7, or about three-fourths of a pound, of potassium.
In the past, if one sought to fertilize their gardens using natural organic sources, often the major nutrients were purchased separately. For instance, bloodmeal or cottonseed meal would supply nitrogen, bonemeal or rock phosphate provided phosphorus, and greensand or wood ashes contained potassium. Now, companies have formulated complete natural organic fertilizers so all three of the major plant nutrients are contained in one package. These are quite convenient for gardeners and are a suitable choice if a soil test indicates that your nutrients are at optimum levels. If a deficiency is indicated, you may have to add more of a particular nutrient in another form, plus the recommended amount of the complete natural organic fertilizer.
Two factors are important to understand when using natural organic fertilizers. The first is that the nutrients in these products are in complex organic and inorganic forms and soil microorganisms are needed to break these large molecules down into inorganic ionic forms that plants can take up. These microorganisms perform poorly under cool, wet conditions or under dry conditions. They also need food and energy to perform these tasks, and that is obtained from organic matter. Ideal concentrations of organic matter in our garden soils would typically be from 4 to 8 percent.
The second is that you can apply too many nutrients with natural organic fertilizers, just as you can with synthetic fertilizers. This causes problems for your plants, and for the environment. Composts and manures can be high in nutrients, and if they have been regularly added to your soil, you may not need to add anything more this growing season. Soil testing is an easy, inexpensive way to tell if you are applying the right amounts of nutrients.
When fertilizing, always use care. Don’t apply more than the recommended amounts, and time your applications appropriately. It is also important to maintain the soil’s pH in the desired range as soil pH plays a large role in determining how available the nutrients are to your plants. If you have questions about natural organic fertilizers, soil testing or other home and garden questions, call, toll-free, 877-486-6271, visit the website www.ladybug.uconn.edu or contact your local Cooperative Extension Center.