Flexible rubber pond liners shielded below and above by a protective underlay liner can with stand the weight of rocks and safeguard the pond liner from possible damage.  However, whether or not to add rocks or pebbles to create a natural pond effect is a much-debated subject discussed by many pond experts. And, the final verdict? There isn’t one. With all the pros and cons to each argument, it comes down to what the pond owner is prepared to do to maintain a healthy pond.

If you are going to add rocks to your pond consider adding a bottom drain at the deepest part of your pond. In addition there are a few other considerations to take into account before going ahead with this pond additions:

• Use large, smooth rocks placed just one layer deep and if you have included a bottom drain, keep a wide area around it free of rocks. Debris won’t get trapped as easily between smooth surfaces plus there is less risk of damage to the pond liner.
• Invest in a pond vacuum cleaner to clean the rock surfaces of debris.

Advantages of adding rocks to bottom of pond

• Hides the pond liner creating a more natural-looking garden water feature
• They provide a surface for aquatic plants to more readily anchor themselves and establish a root system.
• Rocks create a larger surface area on which beneficial bacteria can grow and filter pond water. Ponds need bacteria to break down organic sludge.

Disadvantages of rocks positioned on pond liner

• If a collection of rocks or pebbles are added to the bottom of a pond, they will provide an ideal habitat for sludge and fallen leaves to gather. Once debris has fallen between rocks, it becomes very difficult to remove them. A pond that is free of rocks or pebbles can be easily cleaned using a skimmer or pond vacuum.
• String algae will readily attach itself to the rocks, making it physically more difficult to remove them.
• Colourful pond fish are more readily noticed against the back drop of a black pond liner and less so against rocks.

If you have fish and want to line your pond with gravel, rock or pebbles then the best advice is to be careful about how much you feed your fish.  If there is no excess food left in the water, there is less chance of inorganic matter accumulating at the bottom of your pond risking a change in water quality. Fish keep algae levels under control.

There are pros and cons to both sides of the discussion regarding adding rocks to the bottom of a pond. Both sides will have equally convincing reason fore or against. You need to decide which argument makes the most sense to your pond and how you manage its maintenance through the seasons.