How to Use Salt to Treat Pond Weeds

Updated February 21, 2017

Ponds are a tranquil and attractive addition to any landscape. Not only do they add beauty, but they also attract wildlife such as turtles, frogs and deer. Many home gardeners also raise fish (most commonly koi) in their ponds. Aquatic plants help balance the oxygen level of a pond, add visual interest, and provide a place for fish to hide. They also provide food to some animals. Unfortunately, weeds can quickly overtake a pond, crowding out desirable plants and rendering the pond unusable for animals and fish. Salt is a safe, non-toxic way to get rid of pond weeds.

Sprinkle 1 tsp rock salt around the base of each plant you want to kill near your pond. The salt will absorb the moisture from the soil that usually goes to the plant's roots, according to the University of Vermont.

Add salt to your pond water. Sprinkle it lightly over the surface. Use 35.4gr. salt for every 10 gallons of water your pond contains. If your pond is stagnant, circulate the water manually to spread the salt around.

Test the water with a salinity test kit, available at most garden centres. Note that salt levels of about 0.1 per cent will not harm fish, but will kill aggressive weeds such as water hyacinth. Low levels of salt will also control algae and kill parasites. Common pond weeds such as duckweed and cattails will not die unless your salt content is at or over 0.3 per cent. Fish will start to be harmed by salt after it reaches levels of above 0.3 per cent.

Add salt if the salinity levels are not high enough. Continue to monitor the salt levels in your pond every month.


Killing all the plants around your pond will remove the likely hiding places of frogs, lizards and turtles. It is best to leave some plants so that your pond wildlife will have shelter.


Salt will kill all plants it comes into contact with, so make sure you sprinkle it carefully. In addition, large amounts of salt can render the soil inhospitable to plant life for months or even years.

Things You'll Need

  • Rock salt
  • Salinity testing kit
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