Soil used to line the bottom of ornamental ponds or container-grow aquatic plants must be dense and heavy. Topsoils rich in clay and low in organic matter are ideal because they remain dense while submerged, and do not release floating particles into the water. Creating a pond soil mix centres upon a clean, dense topsoil that's rich in clay. The addition of a well-composted cow manure adds nutrients and an improved texture to soils used in submerged containers.
Obtain topsoil for the base of the mixture. Search your garden for a clay-based soil that has little organic matter in it. Buy topsoil in bags from a garden centre, if necessary.
Place three shovels-full of topsoil into a wheelbarrow. Remove any organic matter such as bark or leaf compost that will float in the pond once the soil is submerged.
Add one shovel-full of well-rotted cow manure to the topsoil. Mix the contents of the wheelbarrow thoroughly with the shovel so there is a consistent blend and texture.
Adding well-rotted cow manure is optional, but recommended if the soil is to sustain plant growth. Clay soils are ideal for use in ponds and submersed plant pots, and dense loams are acceptable as long as organic material is minimal or absent.
Water the pond soil mixture before placing it on the pond bottom or in containers. This will reduce settling and murking the pond water when added.
Do not use potting mixes for pond soil. These mixes contain perlite, compost, fertiliser granules and vermiculite that will not compact and will float in the pond water.
Avoid gathering topsoil from woodland areas, as it will be full of organic matter.
Avoid sandy soils, as they are not dense and can lead to cloudy pond water and plants that do not root well, causing them to float to the surface.