Using Pond Scum as Fertilizer

One man’s pond scum is another man’s treasure. Some biological waste from your pond can be beneficial to your backyard. The sludgy green algae, that you work so hard to prevent and get rid of, is a perfect and essential ingredient in composting. Compost is an organic, natural, and cost-efficient way to fertilize plants and soil.  So now when you are clearing out that algae, you can put it to good use. 

Spring is a perfect time to clean your pond and rid your water garden of pond scum.  It’s also an ideal time to start composting. Composting is a natural process that turns organic material into a dark rich substance that is a wonderful conditioner for your soil. This organic matter is known as the “soul of a healthy soil.” Adding compost to your yard or garden will help your plants grow bigger and better.  It also helps soil hold on to nutrients and water, benefiting your plants while reducing the risk of pollution.  

But why is algae or pond scum good for creating fertilizer?  Pond scum and algae are living organisms that are rich sources of nitrogen, an essential nutrient for the millions of decomposing bacteria at work on your compost. According to the University of Illinois Cooperative Extension, these aerobic bacteria use the nitrogen in compost ingredients, such as pond algae, to grow and reproduce. Using pond scum as fertilizer also incorporates important nutrients, such as potassium and phosphorus, into the compost. A key factor in composting pond algae successfully is making sure that you layer your compost correctly. 


How to turn pond waste into compost 

  1. Remove the algae or pond scum from your pond. The easiest way to remove pond scum is to use a fish net, swimming pool skimmer or a rake.  
  2. Let excess water drain, then place the scum in a bucket for transport. If the water is salty, rinse the scum with a garden hose before adding it to the compost pile.  
  3. Next, mix the algae thoroughly with other nitrogen-rich (green) organic materials like fresh grass clippings, horse or cow manure, coffee grounds, and vegetable scraps.  
  4. Gather a variety of carbon-rich (brown) materials such as straw, cardboard, shredded paper, dead leaves, dried grass clippings and old hay.  
  5. Spread a layer of the carbon-rich organic materials 4 to 6 inches deep on the ground in a 3-square-foot area.  Place a 3-inch layer of high-nitrogen materials, including the pond algae, over the carbon layer.  
  6. Sprinkle several handfuls of plain topsoil over the pile, which introduces beneficial soil bacteria and speeds the process of decomposition and ultimately the composting process.  
  7. Moisten the pile lightly with a garden hose and nozzle attachment.  


Build your compost pile with alternating layers of carbon and nitrogen materials until it is 3 to 4 feet tall. Use a manure fork to push the center of your pile down slightly to help channel rainwater into your compost to keep it moist.  

The pile should heat up within 24 hours. Check the moisture level of your pond algae compost every two or three days. It should feel like a moist wrung out sponge. If you squeeze a handful of the compost material and only a few drops of liquid are wrung out, then that is the correct moisture according to the University of Illinois Cooperative Extension.  

Wait for four to five weeks for your pond algae compost pile to heat up then mix the layers with a manure fork. Continue aerating the compost by turning the layers once every seven to 10 days. 

Once the compost is ready, it will appear dark brown with a crumbly texture and rich, earthy aroma. A few ways you can use the compost as pond scum fertilizer in the garden is to spread up to 3 inches of the compost over the soil just before spring planting, then dig or plow it into the soil, or spread the compost evenly over the soil as mulch. You can also make potting soil for indoor plants by mixing equal parts pond scum compost with perlite or clean, coarse sand. 

Using pond scum as compost will help you save money on fertilizer and trash removal, help the environment by limiting pollution, and give you a new project to work on while improving your backyard.