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How to Kill Sea Grass

sea and grass image by Marzeev Andrey from

Sea grass is an aquatic plant that grows in the saline environment of the ocean as well as estuaries and shallow coastal waters. In the ocean, meadows of sea grass provide oxygen, shelter and food for marine animals. But when sea grass becomes established in a backyard pond it can take over and crowd out more desirable plants. Killing sea grass in a home backyard pond is simple.

Remove desirable vegetation and fish from your pond. Desirable vegetation and fish may be killed in the efforts to rid yourself of sea grass.

Cover your pond with light-blocking cloth such as a tarp. Sea grass is dependent on sunlight to grow. Leave the tarp in place for up to two weeks.

Remove the tarp and uproot dead sea grass plants. Use a rake or cultivator to pull up the roots of the plant along with the dead vegetation.

Apply a herbicide such as copper sulfate to your pond to treat any remaining sea grass. Sea grass is very sensitive to the changes in minerals present in water, and will die if the mineral content changes suddenly. Copper sulfate should be applied at the rate recommended on the bag; the amount may vary between brands. Copper sulfate is harmful to algae, but is harmless to most other pond plants.

Test the pH of your pond with a pH test strip before returning fish and plants to the pond. Copper sulfate is dangerous to fish if the pH of your pond is low. If your pond water pH is lower than 6.0, you can raise the pH by adding baking soda to the water.

Add your fish and plants back to the water.


In many parts of the world, sea grass is considered to be beneficial. Efforts at conserving and restoring sea grass are underway in many locations. You should not consider killing sea grass in estuaries, coves or the ocean.

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