When more can be too much 

DATE:          4/19/01    
WRITER:     Chris Ray, Clemson Fertilizer and Seed Certification, 
                    (864)-646-2145
EDITOR:     Giles Singleton, (864) 656-3876

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When more can be too much:
Avoiding over fertilization

CLEMSON – Spring is here and everyone is eager to get busy in their gardens. Gardeners have visions of lush ornamentals laden with blooms of all shapes and colors, tremendous vegetables, delectable fruits and well-manicured lawns.
            These visions are great motivators to the home gardener; they show the rewards for all those hours of hard work. Unfortunately, at times this same motivation leads to practices that can be harmful to the environment and to our beloved plants – like over fertilizing.
           The old saying “if a pound is good then two pounds is twice as good” does not apply to fertilizing our gardens today.
           All plants have certain requirements like water, nutrients and light. These needs must be satisfied so plants can grow and develop properly.
           However, if we exceed these plants’ requirements there is a good chance that we will do more harm than good, especially where fertilizer is concerned.
           Excessive fertilization can cause unused fertilizer to leach through the soil and contaminate groundwater, and to run off the soil surface after heavy rainfall and contaminate surface water.
           Too much fertilizer -- particularly nitrates -- in groundwater can lead
to a reduction of oxygen in young children’s blood. Excess fertilizer in surface water can increase algae growth in streams and lakes. When the excess algae die, the oxygen level in the water is lowered, which in turn kills fish and other aquatic animals.
           Too much fertilizer can also lead to nutrient toxicity in plants, which can have a variety of negative effects on a plant’s growth and development An example is excessive nitrogen content, which, in flowers and fruits, leads to excessive growth of leaves and stems, as well as reduced root and reproductive growth. Other nutrient elements present in soils at toxic levels can cause a decline in plant growth or death of the plants.  
           Over-fertilization can also cause an unwanted decline in your bank account. If you apply more fertilizer than your plants can use, the excess fertilizer will likely be lost as it leaches from rainfall and irrigation; this translates to lost money.
           Because different plant species and different soil types have different fertilization requirements, the simplest and best way to determine how much fertilizer you should apply is by taking a soil sample to your county’s Clemson University Cooperative Extension office. It is a good idea to call first for instructions on how to take the sample, or go to http://hubcap.clemson.edu/~blpprt/bobweb/bobweb.html, maintained by Bob Lippert, Clemson Extension soil fertility specialist. In addition to the phone book, you can locate your county’s Extension office at: www.clemson.edu/extension.
          If you are going to be applying fertilizer, then it is important to understand how to interpret the information provided on the label of a fertilizer container.
          For example, with a complete fertilizer, one that contains nitrogen, phosphorus, and potassium, the three numbers on a bag represent the percentage of nitrogen (N), phosphorus (P), and potassium (K) contained in the bag. So if a bag of fertilizer has an analysis of 10-10-10 it would contain 10% nitrogen, 10% phosphorus, and 10% potassium.  If the same bag of fertilizer has a net weight of 50 pounds, it would contain five pounds of nitrogen, five pounds of phosphorus, and five pounds of potassium.
         For detailed information on fertilization and other cultural practices relating to specific crops, contact your county’s Clemson Extension office. They can provide advice and literature that will guide you through the growing process from planting to harvesting.
        With spring in the air and planting time rapidly approaching, remember to accurately apply the appropriate amounts of fertilizer to the plants you are growing. If you are good to your plants and give them what they need, you will be rewarded with healthy plants and abundant harvests.
        For more information on fertilizers, check out: http://fscs.clemson.edu

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      If you have gardening questions, write to PSA Media Relations, A-101 Poole Agricultural Center, Clemson University, Clemson, S.C. 29634-0129. You might also want to search our website at: www.clemson.edu/psamedia.

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