Q. What is the best type of rock to line a French drain?
A: Your landscape supply store will likely have a few varieties of stone sold as “drainage rock,” but some of these selections are decorative in nature and more expensive than what you’ll need for a buried trench. For the best drainage, look for coarse washed rock (gravel) that is screened, with a stone size of 1/2 to 3/4 inch. Smaller rock with fine particles could clog the holes of the drain pipe. Pea stone works, but the smooth stones settle together and don’t move as much water as coarse rock. The more rock and larger the trench, the more water the drain can handle and the longer it will perform correctly.