We have recently been using a product from GROW STONE called GNAT NIX. So far we are quite impressed with it. Its basically a top dressing that looks like sand and appears to be larger chunks of Grow Stone, that has been broken down into a smaller finer product. We had used sand in the past to try and block out Fungus Gnats from getting into our soil, but it would tend to end up recirculating into the soil and not really stay on top of the soil. The Gnat Nix seems to hold its position a little better, and really gets into the Nooks and Cranny’s in order to help keep out those little flying pests. If you mess a little up during your watering time, just let it dry for a couple of hours and its easily raked back into place. All that is required is a 3/4″ – 1″ layer, and your good to go. We found this product to be a great alternative to Chemical Pesticides in your garden and Easy to Use!
Here is a video from the company that explains the product a little better.
Our suggestion is to pick some up and see if it works as well for you, as it does for us.