Fertilizing Ponds

If pond owners wish to maximize fish production, fertilizer must be properly applied to increase natural fish food. Properly fertilized ponds normally produce three to seven times more pounds of bream and largemouth bass than unfertilized ponds.  Fertilized ponds also have less weed problems due to the shading effect of darker water.  The application of fertilizer does not prevent fish from biting and the water is safe for livestock and for swimming. 

Before stocking fish, pond owners should decide if a fertilization program will be part of their long-term management plan.  Ponds cannot be fertilized economically if the water stays muddy, or if excessive amounts of water are flowing through the spillway during the spring and summer.  In addition, if fish are not to be routinely harvested, the owner may elect not to fertilize.

Kind and amount of fertilizer:  Fertilizers are typically labeled with percents of nitrogen (N), phosphorus (P), and potassium (K).  For example, fertilizer labeled 20-20-5 is comprised of 20% N, 20% P, and 5% K.  Phosphorus is normally the limiting nutrient in most ponds.  Owners should purchase and apply formulations that will give approximately 8 pounds of phosphorus per acre per application.  For example, 40 pounds of 20-20-5 contains 8 pounds of phosphorus (40 x 0.20). 
One of the following formulations of fertilizer may be used per acre per application:
 A.  50 pounds of 16-16-4 or 18-18-5.
 B.  40 pounds of 20-20-5.
 C.  3 to 4 quarts of liquid fertilizer: 10-34-0 or 13-38-0.
 D.  4 to 6 pounds of powdered fertilizer: 12-49-6 or 10-52-0.
 E.  25 to 40 pounds of annual time-release fertilizer: 10-5-0.

When to fertilize:  Fertilization should be initiated when water temperatures stabilize above 60° F, usually late February to early April, depending on the region of the state where the pond is located.  Fertilization should begin each year at this time in ponds with established populations as well as in new ponds that have been stocked with bream but have not yet received largemouth bass fingerlings.  Applications of fertilizer should continue throughout each spring and summer as follows:
 1. Make the first application when water temperature stabilizes above 60° F (usually February to April).
 2. Make the next two applications at two-week intervals.
 3. Make the fourth and subsequent applications when the water visibility exceeds 18 inches (usually every 3 to 5 weeks). 
 4. Discontinue fertilization when the water becomes cold (below 60° F) in October or November.
 5. Repeat the above steps each year. (Note: Some ponds cannot be effectively or economically fertilized because of excessive flow. Contact the local fisheries biologist, if in doubt.)

Most ponds in Alabama require about 10 to 12 applications of fertilizer each year; however, the time between applications may vary.  Ponds with high lime content or those that receive run-off from a heavily fertilized watershed may require less fertilizer.  Ponds that receive heavy rains or those on moderate streams may require more frequent applications to maintain a desirable plankton bloom. 

Therefore, ponds should be fertilized based on water visibility rather than a regimented time interval.  Visibility refers to a green color from plankton growth, not a muddy color from run-off.  If the green water visibility is over 18 inches, then additional fertilizer should be added.  A 12 to 18 inch green visibility is ideal.  If visibility is less than 12 inches, the pond is too dark and fertilizer should not be added until the water clears to 18 inches or better.  A simple method for checking visibility is with a Secchi disk. Attach a round white object (6 inches in diameter) to a yardstick.  Submerse the object in the pond, then read the inches on the yardstick when the object disappears to determine the visibility.

Many ponds can be fertilized properly with phosphate fertilizers only.  Ponds that have been properly fertilized two or more years with a complete fertilizer, may be fertilized adequately at about one-third the normal cost by using 40 pounds of superphosphate (18-20% phosphate) or 18 pounds of triple superphosphate (46-52% phosphate) per acre per application.  A complete fertilizer should be used for the first two applications each year.  After that only phosphate should be used for the remainder of the year.  If phosphate fertilizer does not maintain a desirable growth of plankton, then revert to the use of one of the complete fertilizers previously described.

The information above came from the Alabama Wildlife and Freshwater Fisheries Division's booklet Sportfish Management in Alabama Ponds, which is available as a PDF.

The Alabama Cooperative Extention System maintains a list of pond consultants.