The Best Rocks For French Drains: What To Know

Are you preparing to install a drainage system and wondering which type of rock is best for French drains? The type of rock used in your French drain is essential because if you choose the wrong type, it can cause issues and prevent your drain from working effectively. 

So, don’t stumble over all the rock choices. Learn which are the best rocks for French drains and which are the worst ones so you can avoid potential issues and an unnecessary purchase. 

Best Rocks For French Drains

It may surprise you to learn that only two types of rocks are recommended for use in French drains, simplifying the decision-making process. Let’s dive into the two most popular rocks to use for this drainage system: 

1. River Rock

River rock tops the list of the best rocks for installing in French drains. Natural round rocks are ideal because their size and shape allows the water to drain more effectively. It’s vital to use washed rock because it has been cleaned of debris and particles, which will help prevent clogging the drainage system. River rock is also durable and can thwart off the erosion effects of water. The average cost for a ton of river rock ranges between $100 and $800, but may vary depending on your location.

Best for: Homeowners installing a French drain on a budget

2. Granite Chips

Granite chips are another top pick when it comes to the best rocks for French drains. Granite is also a hard rock that is durable and resistant to erosion. Due to the shape, size, and density of granite chips, the material allows water to flow freely, which ensures the drain works efficiently and prevents clogs. 

However, granite can be more expensive than river rock, so you will want to compare prices and determine which type of rock is best for your project and budget.

Best for: Homeowners prioritizing aesthetic appeal of French drain

Worst Rocks for French Drains

Rocks that are too small and dirty can cause issues and prevent proper drainage. So, now that you know the best rocks for French drains, let’s explore which ones you should skip.

1. Pea Gravel

For water to flow freely, there needs to be adequate spacing between the rocks. Pea gravel is not a good choice to use for a French drain because the size of the rocks are too small. It also compacts more easily, which prevents proper use of the drainage system. 

While pea gravel is eye-appealing and excellent for other landscaping projects around your home, such as walkways, you should skip using it for your French drain system. 

2. Limestone

While limestone is a durable rock, it is more susceptible to erosion than other rock types. Acidic rainwater can cause limestone to dissolve and erode faster. As it breaks down, the fine particles can wash into the drainage pipe, causing clogs and preventing it from draining properly. 

Limestone can be a great choice for other landscaping purposes, such as decorative rock gardens or pathways, but you want to avoid using it in your French drain installation.

What is the Best Size Rock to Use for French Drains?

The size of the rocks is as vital as the type of rocks for your French drain. The best size rock to use for French drains is between ¾ inch and 1½  inches. If the rocks are too small, they will not allow proper water flow, which prevents efficient drainage. Rocks should be large enough to create space between them to allow water to flow freely and prevent blockages. Consult a local French drain installer to ensure the rock type and size is a good fit for your drainage needs.