I use a layer of granite grit (used as poultry grit or roofing grit) on all my seed pots. It does help keep the gnats from the organic soil beneath, and it prevents the seeds from washing when they are watered. Richard Vista CA -----Original Message----- From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Stokman Sent: Thursday, March 24, 2011 11:21 AM To: pbs@lists.ibiblio.org Subject: [pbs] Fungus gnats I don't know if it would be possible in a large commercial operation but years ago I read that pouring a layer of sand on top of the soil in a pot would eliminate fungus gnats, reportedly because the sand cut up gnats or their larva, I'm not sure which. Can't beat that for organic, My purely anecdotal and sporadic observation is that it works, though the sand needs to be periodically replenished if the pot is watered from the top. zone 8/9, Sierra foothills