Substrate Choices for Ponds: Gravel, Soil, and Koi Considerations

What Goes on the Bottom of a Pond?

Pond substrate varies by design and inhabitants. Some ponds use gravel or soil, but both must be free of pollutants and fertilizers. However, koi ponds typically have no substrate, gravel, or plants—just a bare liner. This simplifies cleaning and maintains water quality for koi, which are messy and uproot plants.

Substrate Guidelines

• Wildlife/natural ponds: Soil and gravel support plants and microorganisms.
• Water garden ponds: Gravel on shelves and bottom anchors plants and aids biofiltration.
• Koi ponds: Bare liner preferred; bottom drains remove waste efficiently.

Always rinse gravel thoroughly before use. Avoid limestone or materials that alter pH. For koi, a bottom drain and external filtration are more effective than substrate-based systems.