Pond Fertilization
Galen Jons, Fisheries Biologist

Most pond owners are interested in increasing the quality of fishing in their ponds. Two common ways to do this are increasing the fish population and increasing the size of the fish. One of the most cost-effective methods of doing this is fertilization.

Pond fertilization is the application of nutrients (commonly nitrogen, phosphorus and potassium) to the water to increase growth of microscopic plants and animals collectively referred to as plankton. Plankton provides food for insects, which in turn provide food for small fish and crustaceans, which in turn provide food for larger sport fish.

Following is a guide to help produce the most successful fertilization program:

First, determine if the pond is muddy. If so, then fertilization may not work, as sunlight is necessary for the microscopic plants to grow. See the page on clearing muddy ponds to fix this problem prior to fertilizing.

Second, make sure you don't have aquatic weeds present. Weeds will use up the fertilizer before the plankton can utilize it. If weeds are present, the most effective short-term control is with chemicals. Contact your local county extension agent for assistance. Once fertilization begins, the resulting plankton blooms should prevent further weed growth.

Third, if your pond contains many rough fish, you may consider renovating the pond. See the "Renovation Of Farm Ponds" handout.

Fourth, determine if your pond has a lot of water flowing through it. Although this isn't a problem in most West Texas ponds, if you're lucky enough to have a pond that usually has water flowing through it, fertilization may not work since it will likely be washed out.

Finally, if you are feeding catfish in your pond, you probably don't need to fertilize. Excess catfish feed, as well as increased catfish waste, will usually provide plenty of fertilizer in the pond.

Now you are ready to select a fertilizer. We recommend inorganic fertilizer, in either granular or liquid form. Read the following, then determine what will work best for you based on cost, availability and ease of application.

Select fertilizer formulations that are high in nitrogen and phosphorus, such as 10-34-0, 16-20-0 or 20-20-5. Phosphorus is usually the limiting nutrient, and after several applications of nitrogen, phosphorus may be all that is needed.


If using fertilizer containing ortho-phosphates, it should not be stored where it will be subjected to low temperatures, such as unheated buildings during winter. Fertilizer containing polyphosphates can, however, be stored at lower temperatures.

This fertilizer should be dissolved slowly into the water. Never just dump a bag into the pond, as most of the fertilizer will immediately go into the soil and not be available to aquatic life. The most effective method is to build platforms out of plywood to hold the fertilizer. Usually, one 4-foot-square platform is enough for a five-acre pond. The top of the platform should be about one foot below the surface of the water. Alternatively, a slit can be cut in the side of the fertilizer bag, and the bag laid in shallow water with the cut side up. Start with 100lbs. granular fertilizer per acre, and follow up with 50lb. applications as needed (see below).

Liquid fertilizer is heavier than water and must be diluted with water before application. Otherwise, it will sink to the bottom and not be available to aquatic life. Mix 1 gallon fertilizer with 10 gallons water in a mixing tank, then spray onto the surface of the water. In larger ponds, the mixture can be mixed into the water with an outboard motor. Start with 2 gallons liquid fertilizer per acre, and follow up with 1-gallon applications as needed (see below).

Begin fertilizing once the water temperature reaches 65 degrees, and continue until fall when water temperature drops to 70 degrees. A week or two following the initial fertilization, the water should take on a green color. To check for proper rate, submerge your hand into the water up to your elbow. If you can see your extended thumb, you may need to fertilize more. If you cannot see your thumb, more fertilization is not necessary. Use this method to check your pond every 2 - 4 weeks throughout the summer to determine if and when more fertilization is needed.

Record the dates that fertilizer is applied, how much is applied and the results. This will help provide a basis for subsequent fertilization programs, and help in identifying any problems that may arise.

NOTE: Once fertilization begins, it is important to keep doing it! One-time fertilization usually causes more problems than it is worth, and may lead to poor fish growth in the long term. A continuing fertilization program, however, can easily quadruple fish production in your pond.

Oxygen problems
Pondowners who fertilize need to be aware of oxygen depletion problems. The plankton blooms created by fertilizer create oxygen during the day, but use it up during the night and on cloudy days. If you have a heavy plankton bloom and have several cloudy days in a row, you may run into oxygen problems. To check this, visit your pond at daybreak and look for signs of low oxygen, such as catfish breathing air at the surface. If this occurs, you will need to aerate the pond.



Texas Parks and Wildlife Dept.
5325 N. 3rd
Abilene, TX 79603
(915) 692-0921

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