Fish heads and entrails have been used as fertilizer for centuries. Native Americans would bury a fish head in the soil, then place kernels of corn on top and cover with earth. You can take advantage of this natural fertilizer by using leftover parts from the fishmonger at the market, or by saving the bits you don't eat after a successful fishing trip.
Dig with a shovel around the edges of an existing plant's root structure, or dig six to eight inches deep when preparing to plant a new garden. The soil must be loosened to a depth of at least six inches to prevent animals from digging up your fish fertilizer.
Place fish heads and entrails in a five-gallon bucket and pour in just enough water to cover the guts.
Add a cup of Epsom salts to accelerate decomposition.
Cover the bucket tightly and store outside for 24 hours.
Pour two to three cups of the fish remains into the tilled soil, separating each scoop by about one foot in the garden.
Plant seeds directly over the fish remains or pack the soil over the fish parts in an existing garden.
Tamp down the soil with the flat side of the shovel to pack the earth tightly and discourage foraging animals from digging in your garden.