How to Compost Seaweed in a Plastic Bag

Rinse seaweed in cool water, washing away loose sand, most exterior salt and bugs.

Lay your seaweed on a surface to dry overnight. The surface can be a driveway, plastic-lined picnic table or any other surface that does not hold moisture.

Chop or cut the dry seaweed into fine pieces by using a small hatchet or sharp shears.

Mix the seaweed pieces with twigs, leaves, grass cuttings and any other organic debris you raked from your yard. Place the mixture in a large, plastic trash bag.

Add soil and high-nitrogen fertilizer to the seaweed and organic debris in the plastic bag. Keep the proportions to about 1/4 cup of fertilizer for every 4 cups of soil. You do not have to mix the fertilizer with water.

Mix the plastic bag's seaweed, organic debris, soil and fertilizer thoroughly with a trowel.

Seal the plastic bag with a twist tie or rubber band, or by tying a knot in its open end. Poke about one dozen holes in the bag with an ice pick or the tip of a sharp knife.

Place the bag in a warm place where it will not be disturbed. Check the seaweed's condition about every two weeks. The seaweed is ready for use as compost when it is black and crumbles easily between your fingers. It may be ready for use in as little as two weeks or as long as six to eight weeks in a cool area.

Combine the seaweed mixture with topsoil as soon as the mixture is ready for use. Spread it throughout your garden or wherever your soil needs enrichment.