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Understanding Fertilizers for Your Yard and Gardens

University of Minnesota Extension, Stearns County News
February 8, 2017        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton, & Morrison Counties


Understanding Fertilizers for Your Yard and Gardens
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (02/08/17) — All plants need nutrition, so understanding fertilizers whether organic or synthetic are important to good plant health, growth and production.  Plants need varying levels of primary, secondary, and even micro nutrients for growth and production of proteins and carbohydrates. An added bonus to using organic fertilizer such as manure is the improved soil structure; which is the space provided in the soil for root growth, and water and air movement.

The primary or macronutrients are those needed in the largest amount and include nitrogen (N), phosphorus (P), and potassium (K). Fertilizer bags are labeled with an analysis of the composition of N, P, K. For example a 10-6-4 fertilizer contains 10% nitrogen, 6% phosphorus, and 4% potassium of the overall net weight. Therefore a 50-pound bag would contain 5-pounds nitrogen, 3-pounds phosphorus, and 2-pounds potassium. The other weight is just filler.

Secondary nutrients needed by plants include: calcium, magnesium, and sulfur. The micronutrients some even considered trace elements, which are needed in very small amounts, are boron, copper, chlorine, iron, manganese, molybdenum, and zinc.

Nitrogen is necessary in plants to create amino acids which is a key component in forming proteins, nucleic acid (DNA and RNA) and chlorophyll.  Chlorophyll is what gives the plant its green color and is necessary for the plant to photosynthesize where they take in water, carbon dioxide and sunlight, and make oxygen and carbohydrates. Plants are able to photosynthesize at higher rates if there is ample supply of nitrogen and in turn will have lush growth and be a healthy dark green in color.

Phosphorus is an important factor in the plant’s complex energy transformation and regulates protein synthesis therefore it is vital in cell division and plant growth. Phosphorus is also critical in promoting root growth, winter hardiness, stalk and stem strength, and flower and seed development. Inadequate phosphorus is hard to identify but will result in stunted plant growth and may result in purpling of the leaves and stems.

Potassium is the final macronutrient which relates to water, nutrient, and carbohydrate movement in plants. Potassium is tied to enzyme activation in the plant that impacts protein, starch, and adenosine triphosphate (ATP) production. ATP regulates photosynthesis, and the opening and closing of the stomata which regulated water vapor, oxygen, and carbon dioxide exchange. Potassium contributes to increase root growth and increases drought resistance. Deficiency of potassium also results in stunted plant growth and reduced yield.

It is impossible to determine nutrient levels simply by looking at the soil, therefore a soil test should be completed to give an analysis of the nutrient content. Soil tests can be done at the University of Minnesota Soil Testing Lab, information available at or there are a few private testing laboratories throughout Minnesota.

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