The numbers listed fertilizers packaging have significance and provide gardeners with important information that goes to the fertilizers’ makeup percentage of each element: Nitrogen (N), Phosphorous, (P) and Potassium (K) (image courtesy: pintrest.com).
By John Green, Texas Certified Expert Gardener, Orange County, TX
Most of our spring ornamental flowers have succumbed to summer’s intense heat and elevated humidity! There are a few stragglers remaining, lingering in tucked away areas where a ‘touch of shade’ has provided them recourse from the blistering afternoon sun.
There are many types and varieties of fertilizers available for gardeners to purchase and offered in multiple forms. For us to understand why fertilizers are needed when growing plants, we first need to discuss a plant’s nutrient requirements. Plants require six macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, and potassium. The latter three nutrients come from the soil. Before purchasing fertilizers, it is important to know if the soil holds “freely” available nutrients necessary for optimal plant growth and overall health. Before purchasing or applying fertilizer formulations to an area, it is always best to begin with a soil analysis.
Soil Test
Let it be known that the very first step in any gardening endeavor begins with a soil analysis! Reach out to the local County Extension office in your area, they will provide gardeners with details on how to capture samples and where to send the samples for accurate and useful results. The soil results are needed because soil is constantly changing, and my recommendation is to have your soil tested every 3 to 4 years. Good record keeping is important for soil test results, fertilizer applications, soil amendments, and plant rotations.
Primary Macronutrients
Labeling (N-P-K)- macronutrientsare listed oneach fertilizer container label with information which specifically details the amount (percentage) of nitrogen, phosphorus, and potassium (industry standardized order) of the fertilizer formulation. Three numbers are listed in series, providing the percentages of each nutrient (N-P-K) by weight. Some ‘general purpose’ fertilizers such as 8-8-8 or 10-10-10 have equal ratios of corresponding nutrients and other special purpose fertilizers are formulated specifically for root or foliage growth.
Nitrogen- is needed for leaf growth in plants such as turfgrasses, which are all leaves that require a significant amount of nitrogen. Lawns need fertilizer formulations with larger first numbers and this is why turfgrass fertilizer formulations have elevated nitrogen levels with formulations such as 24-4-12 and 20-2-6.
Phosphorus- encourages root development that strengthens plants’ root systems, “fastening” them into the soil. This nutrient is necessary for increased inflorescence (blooming) and fruit production. Night shade plants such as tomatoes, potatoes, eggplant, peppers and root crops appreciate fertilizer formulations such as 5-10-10.
Potassium- is needed by plants to protect them against diseases and to maintain vigor by enabling them to withstand temperature extremes (up to a point) and ward off disease. Also known as potash, plants which are deficient in potassium will display underdeveloped leaves and fruit, often becoming drought intolerant. Most soil contains potassium which is why the third number in the fertilizer formulation is often the smallest.
Secondary macronutrients
There are other ‘key’ nutrients that plants require but in more limited quantities. The nutrients listed are required for plants to thrive.
Calcium (Ca)- promotes the growth of young roots and improves the overall vigor of the plant.
Magnesium (Mg)- is important for effective photosynthesis to occur. Magnesium regulates nutrient uptake from the soil, aids in the dark green color of leaves and seed formation.
Sulfur (S)- is necessary to maintain the ‘rich’ dark green color while encouraging plant growth.
Micronutrients
Nitrogen, phosphorus, and potassium are not the only nutrients plants require for survival and growth. Trace minerals are needed in the smallest of quantities but are required for overall plant health. These minerals include boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc. Gardeners need to have soil tested. The lab results provided from the soil analysis will highlight recommendations to add minerals found to be deficient.
Organic vs Synthetic Fertilizers
Organic fertilizers– (always my preference) include blood meal, cottonseed meal, feather meal, seaweed, fish emulsion, or crab meal, are always my first choice and least harmful the environment. These type fertilizers work with soil microbes which assist in breaking down fertilizers for faster nutrient uptake without adding excess salts or acid to the soil. Organic fertilizers are hugely beneficial to the soil, encouraging healthy soil microbiome through increased microbial growth.
Organic fertilizers will enrich the soil but need time to do so. Applying in the fall will allow the nutrients to be available for spring planting. For the spring, some fertilizers combine the best of both worlds with an organically based fertilizer mix which may also contain small amounts of synthetic fertilizers for immediate availability of nutrients. It is important to note that the “N-P-K” ratio listed on organic fertilizers is lower than the synthetic counterparts. The ratio label can only list nutrients which are immediately available.
Synthetic fertilizers- are derived from compounds similar to ammonium nitrate, ammonium phosphate, superphosphate, and potassium sulfate. These compounds expedite plant growth and contribute to the bloom rate in flowering plants. Unfortunately, chemical derived fertilizer formulations are high in salts which will become detrimental to the microbiome within the soil and the beneficial microorganisms suffer with populations diminish. Chemical fertilizers also tend to ‘migrate’, leaching into waterways after application. Over-application of synthetic fertilizers can “burn” plant roots and damage foliage. Synthetic fertilizers do not improve soil’s health, structure, or fertility for the long-term. Caution is needed since these type fertilizers are highly water-soluble, often polluting watersheds, rivers, and streams creating significant algae blooms which leads to numerous other environmental concerns.
So long for now fellow gardeners! Let’s go out and grow ourselves a greener, more sustainable world, one plant at a time! Gardening questions answered: jongreene57@gmail.com.
Social Media