Why Pea Gravel in the Pond and Cobblestone Aren't the Best Choice
We cleanout a lot of ponds. We see a variety of material at the bottom of these ponds. We see bare liner, giant rocks, flagstone, gravel, rip rap, pea gravel and cobblestone. Did you know that it MATTERS what you have in there are how deep it is? It does!
Pea Gravel in the Pond
We often come across pea gravel. I know that it seems like a good idea, however, there are a couple of reasons why it is not a good choice. While the small size seems good for bacteria, it is so small that it is easily moved. It doesn’t stay in place and even the koi will even pick it up and move it themselves! But the worst part about pea gravel is that it makes it very hard to clean the pond. The size of it makes it impossible not to suck up with a wet vac or move it while pressure washing. It can even get sucked into a pump that is directly in the pond (rather than in a skimmer). When it gets into a pump or wet vac it can damage the equipment. We also find that people put in A LOT of it! When pea gravel is deep, it becomes a muck filled mess.
This is a close up of pea gravel fresh from a bag before it has been added to a pond.
Cobblestone
A bit of cobblestone is fine. However, filling a pond with it can be a giant pain in the neck (or ankle). First, these fist-sized rocks create large gaps when stacked together, which we refer to as muck traps. Second, walking in a pond full of cobblestones is an ankle breaking waiting to happen!
I do like to have some cobblestones around to prop up a newly installed plant or fill an odd space on the pond’s edge, but they are not ideal for use within the pond itself. Did I mention they also get covered in algae? They do.
3/4" Gravel - A very Specific Solution
When we build a pond we use 3/4″ gravel. Why SO specific?
- It’s easy to walk on.
- It won’t hurt the liner even when people or animals need to step on it.
- There is hardly ever algae on it! This size gravel makes the best nooks and crannies to support the colonization of beneficial bacteria! In my pond, algae does grow on the larger rocks but I almost never see it on the 3/4″ gravel. Of course the larger boulders have to be there for supporting the structure of the pond, but this type of gravel works well to fill in the cracks and cover up the liner.
This is photo of the gravel in my pond. If you have pea gravel or cobblestone covering the bottom of your pond, you don’t have to freak out and remove it all today. Each time you are doing pond work just have some of it replaced. And, if you are having it professionally cleaned, you might consider giving the crew a tip!
Kristi's Tips
Remember that the rock (hopefully 3/4″ round rock) does not have to be more than a couple inches deep in the pond. Just enough to protect the liner from UV rays.
3/4″ gravel is great to put around the root ball of new pond plants.
If you are getting a lot of green, pea soup water right now, you may need to change your UV bulb (if you have one).