As warm temperatures rapidly approach, it is time to think about the nutrient needs of both your turf and your garden. Most homeowners will just apply the most readily available fertilizer on the store shelf or gladly pay a lawn maintenance company to do it for him or her. However, simply adding fertilizer to the soil to allow for optimum plant growth does not always guarantee success. The reason is that the 17 known essential elements, also referred to as minerals or nutrients in the gardening world, do not react all in the same way, not in the soil nor in the plant itself. Some move readily in the soil and within the plant. Some do not. In addition, each nutrient has its particular function in the plant and those nutrients interact with each other. When one or more is deficient (or less commonly, in toxic amounts), the plant suffers.
The list of essential plant nutrients includes carbon and oxygen, obtained from the air and hydrogen obtained from water; the air and water can be in the atmosphere or below ground around the soil particles. The rest are obtained from the soil. The three primary macronutrients (ones listed on the numerical part of a bag of fertilizer such as 10-10-10) are nitrogen (N), phosphorus (P), and potassium (K). The three secondary macronutrients are calcium (Ca), sulfur (S), and magnesium (Mg) and the last tertiary macronutrient is silicon (Si). The micronutrients include boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), selenium (Se) and sodium (Na). All of these essential nutrients play some role in the metabolism of plants. Metabolism is the set of life-sustaining chemical reactions of living organisms. Simply put, the essential nutrients are needed to keep living things alive.
Can you determine if a nutrient is lacking by looking at a plant? Yes, but it is not easy. Nutrient deficiencies can mimic other problems such as a reaction to toxic chemicals in the air or ground or an initial reaction to a disease or insect problem. To complicate matters further, a nutrient present at a low level in the plant may cause symptoms that look exactly the same when that same nutrient is present at a toxic level. Or the lack of one nutrient in the plant tissue may look like a toxic level of another.
So, where does one begin? Know what the plant looks like when it is healthy. Next, look for signs of insects and disease. Look around at the environment to see if any herbicides are being applied. Check the root system for damaging nematode activity or possible damage from poor drainage. Look closely at the leaves and determine which look healthy and which ones don’t. Disease and insects normally affect the whole plant. However, nutrients either move or they don’t. In the horticulture world, they are defined as immobile or mobile. So, when looking at a plant with a nutrient deficiency, one part of the plant appears healthy and one part doesn’t. Nutrient deficiencies often first manifest themselves with a mild yellowing of the leaf tissue (chlorosis). If the yellowing appears in the older leaves, with younger leaves looking the proper green, the nutrient is mobile. When in deficient amount, the plant moves the nutrient up to the new leaves. Mobile nutrients include nitrogen, phosphorus and potassium. If you see yellowing in only the new leaves, the problem may be a deficient amount of an immobile nutrient such as calcium, iron, manganese, zinc, copper and boron. For example, calcium stays in the older leaves causing devastating effects on new shoot and bud development.
Keep in mind that even if a nutrient deficiency is correctly diagnosed, the solution may not be simply adding fertilizer. The problem may be the soil pH (acidity or alkalinity), which affects the uptakes of nutrients into the plant. The nutrient may be in the soil but the plant can’t absorb it. Adding more of the nutrient won’t help until the pH is adjusted. In addition to soil pH, soil temperature and soil moisture also affect nutrient uptake. Nutrients are in adequate quantities but simply can’t move into the plant. And sometimes, a limited availability of one nutrient in the soil may cause a deficiency of another nutrient simply by affecting the plant’s ability to transport the second nutrient. So, it is actually two nutrients now deficient inside the plant but actually only one deficient in the soil. Yikes! Makes you want to throw up your arms in defeat!
This is the major reason that it is encouraged to have the soil tested before any application of fertilizer. A soil test will indicate the amount and type of nutrient present, the soil type/organic matter content and the pH of the soil. It will also tell you specifically what nutrients to apply, in what quantities and how to adjust the pH if necessary. Once medium or high fertility levels are established, lawn and ornamental areas need to be sampled every two to three years. Vegetable gardens should be sampled every 1 to 2 years. Results will take 7 to 10 days from the time the county extension lab receives the samples to the time you get test results back. Contact our local county extension office at (912) 554-7577 for soil sampling bags as well as a bulletin explaining the proper technique. Whether you then chose to add an inorganic fertilizer combo of fast/slow release nutrients or organic matter is up to you. Mineral (nutrient, element) uptake by the plant roots functions in the same way whether the source of minerals is from one or the other. If deficiency is affecting plant health, I recommend inorganic fertilizer because it provides a more rapid supply of nutrition. Otherwise, I usually recommend a combination of both. The function of organic matter in the soil is to slowly supply inorganic elements for the plant and at the same time to improve the structure of the soil in an optimum condition for plant growth and nutrient availability. Organic matter must first undergo decomposition into the basic inorganic elements by soil microbes (dependent on soil moisture and temperature. It also takes a lot more organic matter to change soil fertility than a concentrated inorganic fertilizer source of nutrients. If a soil test shows nutrients in sufficient amounts, I still recommend the addition of organic matter to any gardening project because it improves soil structure and quality as it aids in moisture retention and benefits the soil microbial world.
Finally, another method of determining what nutrients are in the plant is through a foliar analysis. This test provides data on the amount of nutrients actually taken up by the plant. Leaf analysis can be helpful in detecting nutrient deficiencies before they affect plant health and yield. In severe deficiency cases, it is recommended that both tests be performed. Results will help the grower to obtain maximum high yield in agricultural production and in fruit and nut orchards. My husband, a certified arborist, uses both to assess tree health. I’ll be using it for the first time in the hydroponic operation using a test of the nutrient tank solution in conjunction with a foliar analysis of the plants being grown.