How to Fertilize a Pond


Fertilizing a pond increases the amount of fish. Adding the correct amount and type of fertilizer promotes the growth of small green plants called phytoplankton. Fish will eat the green plants and in turn increase in size. Typically, an unfertilized pond will yield approximately 100 pounds of fish per surface acre. A fertilized pond can yield as much as 300 to 400 pounds of fish in the same area. By following a basic process you can fertilize a fishpond.

Things You'll Need

  • Visibility stick
  • Pond fertilizer
  • Pocketknife

Check the algae bloom in the pond. Use a visibility stick that is 36-inch wooden stick (old broom handle) with a shiny tin can lid attached to the bottom. Submerse the stick into the water where the shiny lid is 18 inches below the water's surface. If the lid is visible, the pond needs to be fertilized. If the lid cannot be seen, the pond is okay.

Add 40 lbs. of 20-20-5 pond fertilizer per surface acre of the pond. Cut a slit, in the shape of the letter “H” into the flat side of the paper bag, using the pocketknife.

Peel the flaps back and lay the bag in a shallow area of the pond, open end up. The bag needs to be submerged under the water. Lay the bags at intervals around the pond for larger bodies of water. This will evenly distribute the fertilizer.

Apply the fertilizer every two weeks during the warm months, beginning in early spring once the water temperature reaches 60 degrees F. Continue throughout the summer and into early fall until the temperature drops below the 60 degree F mark.

Wait three to four days in warm weather with plenty of sunshine after each application. Test the pond for visibility again. It may take up to a week for a steady bloom of the algae to become established.

Tips & Warnings

  • Ponds that have a large water exchange, less than 30 days, may not benefit from fertilization as the water can flush out the nutrients. Check the pH level of the pond every four years. Adding lime to the water maybe be needed to effectively use the fertilizer.
  • Ponds with heavy vegetation, such as weeds should not be fertilized. The extra phytoplankton may cause the pond to lose oxygen and kill the fish.

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