Is Freshwater Seaweed Safe to Use in the Vegetable Garden?

Identification

• The algae that live in lakes and rivers are typically green algae. These may be native plants, such as the Cladophora, or imported plants, such as Egeria densa. These freshwater seaweeds can quickly proliferate and create problems by forming thick, nutrient-rich mats of vegetation. This lush greenery can be an excellent fertilizer for a vegetable garden, but you must compost it first.

Safety Concerns

• Thoroughly composting freshwater seaweeds reduces the risk of any pathogens. University of Wisconsin Sea Grant Institute researchers studying Cladophora cite concerns about E coli contamination of beached seaweed mats. In addition, water quality specialist Victoria A. Harris initially raised concerns about small amounts of heavy metal contamination from Cladophora growing in Lake Michigan waters. In a 2009 study, however, researcher Mary L. Seaman endorsed using composted Cladophora on vegetable gardens, as well as flower gardens.

Home Composting

• To compost freshwater seaweed for your vegetable garden, Seaman's studies suggest a ratio of 75 percent seaweed to 25 percent wood chips works best. Using composted freshwater seaweeds provides a good source of fertilizer for your vegetable garden, while keeping the gathered seaweed out of landfills.