I don't clean the gravel, per se. I do pick up the leaves that accumulate there and toss them into the bushes - it's never more than a couple of handfuls every week or so. And no - we get very little plant matter in the pond. We have one crab apple that drops leaves on the pond, but they are super lightweight and get pushed out before they can sink. We get some leaves blown in from neighboring yards, but I've already scooped them out this year and had less than one net-full. I put off trimming the plants around the pond until spring as they help to collect the dead leaves on the edge before they can end up in the pond. And I keep my pond plants trimmed up pretty much during the season so nothing drops into the pond.