Using Stone as a Bottom Medium for a Pond

Should I put stones in the bottom of my pond?

Yes, stones in the form of rounded river pebbles can be placed at the bottom of your pond which is used exclusively as a bottom medium. However, there are both pros and cons when using stones as the only form of bottom medium. In the article, I’ll look at them both.

First of all, exactly what kind of stones are we talking about here?

I’m assuming we’re talking about river pebbles or something similar. River pebbles, in different sizes, are available at various home improvement stores and most businesses who sell different types of stones exclusively.

Using Stone as a Bottom Medium for a Pond

I’ll first address river pebbles and their somewhat larger versions. Later in the article, I’ll talk about larger stones and rocks you shouldn’t add to your pond.

The aesthetic beauty of river pebbles

First and foremost, I’ll first mention the aesthetic beauty of having river pebbles in and around your pond. They have nice colors and give the appearance of consistency in a landscape. You really can’t find something nicer to go with than these pebbles when it comes to the overall appearance. While river pebbles aren’t exactly cheap, I wouldn’t consider them excessively expensive. You’ll pay more for them by the bag. You might find them cheaper buying directly from rock and stone distributors.

Note that sometimes after you buy a certain amount of bags, some home improvement stores offer a quantity discount which is more reasonable. The first thing you’ll notice when dumping out a forty-pound bag of river stone is that they don’t cover much space. You need a lot of bags for significant coverage. This is why I suggest either buying them in mass quantities or from a local stone distributor who only deals with large orders. Any stones added to your pond must be thoroughly washed. If exposed to salt water, other contaminants, or other nonconducive minerals to freshwater ponds, be sure they get sterilized properly.

Beneficial pond bacteria

More importantly, beneficial bacteria vital to the ecosystem of your pond grows well in river pebbles. Especially when they’re a couple of inches in depth which is my recommendation when using them. I go at least four inches with such pebbles. It seems beneficial bacteria take better to river pebbles than sand which is my primary bottom medium. Besides aesthetic beauty and the growth of beneficial bacteria, we’ve pretty much reached the end of the benefits of using river pebbles. Lastly, I’d squeeze in that most plants easily root in river pebbles without a problem.

The cons of using only river pebbles or similar stones in your pond

River pebbles aren’t particularly easy to clean when sludge at the bottom of the pond builds up. Sludge is basically organic waste that builds up over time. This includes fallen leaves, other vegetation, sticks, branches, and much more. No matter the placement of your pond or how careful you are, sludge buildup in an eventuality. Even natural ponds and lakes have sludge buildup at their bottoms.

Pond sludge buildup

I remember swimming in lakes in upstate New York during the hot summer months. I could feel the sludge with the bottoms of my feet. It’s simply a buildup of organic waste which eventually breaks down completely. When it does, new organic waste is waiting to take the place of the old. A perfect natural cycle in ponds or lakes but not particularly pleasing in a garden pond. Personally, I allow sludge to go through its natural process. If sludge becomes a problem in your pond and you feel it destroys aesthetic appeal, you can buy a vacuum engineered specifically for sludge buildup. After a few years, if I feel I’m losing any significant amount of depth due to pond sludge, I’ll invest in the vacuum.

What bottom medium I use for my ponds

Here’s what I do for my own ponds. For the most part, I use a mixture of my native sandy soil and rounded river pebbles as a bottom medium. When it comes to the area of my overflow and spillway, I use only river pebbles filling them to the water level. I do this specifically because of torrential downpours. The excess water filters through the river pebbles while small fish cannot be washed through ending up in the spillway.

Pond overflow | Natural Pond Lover
A pond overflow

This is where I find river pebbles (and flagstone) used most effectively and I highly recommend it. While on the subject, if your pond doesn’t have an overflow, you seriously need to put one in. There’s more to having a proper overflow besides just saving some fish. 

Sharp stone warning

River pebbles in both small and larger forms are not always perfectly rounded. I pick up any pebbles or stones with sharp edges in order to protect the pond liner. While not the number one cause of pond liner damage, it’s best to avoid putting anything sharp that depends on a plastic or rubber liner to hold water.

Larger decorative stone

I have nothing against using large decorative stones as long as they are clean and well-rounded. Avoid large sharp stones both in and around your pond. Sometimes, a beautiful but sharp stone placed at the shoreline ends up falling into the pond. While damage isn’t a certainty, I wouldn’t take the chance. I’ve already been through replacing a damaged pond liner once for a rather large body of water. I’d never want to do it again.

Flagstone around the overflow is also sharp by design. I always place the flagstone in such a way that it doesn’t come loose easily. It’s easy to adjust flagstone to fit together nicely.

Do not place the following stones in your pond

Any stone that spent time in salt water or any contaminated by oil, gasoline, herbicides or pesticides. Avoid painted stone and pieces of concrete. Stay away from sea shells, they often carry containments which harm fish. Crushed seashells are very sharp and pose a threat to your pond liner. When using bagged river pebbles bought from your local home improvement center, be sure to thoroughly rinse all the soot and messy particles out in a wheelbarrow or large strainer.

All stones must be clean when placed in the pond or they’ll contribute to poor water quality. Eventually, the excess particles fall to the bottom within the stones. Still, rinsing off excess sediment is the smart way to go and saves time in the long run.

Using Stone as a Bottom Medium for a Pond