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Will a top layer of aromatic cedar mulch, which repels fungus gnats but has fungicidal properties, hurt mycorrhizae or other beneficial soil organisms?
I use a fir bark mulch in the containers on my balcony in Brooklyn, NY. We've had a rainy Spring/Summer here, so the mulch is a little fungy, which I want (right?). But Brooklyn is lousy with fungus gnats from the rain. Plus, I'm brewing a fungal tea, which basically seems to act like a neon "All-You-Can-Eat" sign for the gnats.
Breaking the local breeding cycle on my balcony isn't working because there are plenty more gnats around. I've tried intensive BTi. I keep mosquito dunks (in stretched and tied nylon knee socks) in my dechlorinated watering cans. No help. Nematodes (ScanMask Steinernema feltiae) seem to work for a few days, then not.
I think I don't want a physical barrier like a layer of sand under the fir mulch because I want the mulch to communicate with the soil, right? So that leaves repellents.
I can't stand citronella. On the other hand, I love cedar. I've had some short-term success controlling the gnats by painting GoGnats (33% cedar oil, plus water and a surfactant (sodium lauryl sulfide)) onto the outside of the containers, but the cedar oil evaporates after a few days or gets rained away, and after several applications the surfactant is building up and making my balcony slippery after it rains. Also, I'm concerned about the effects if the surfactant gets into the soil, and it's labor-intensive to paint it on. Plus, I'd like to have the repellent on the entire top surface itself, instead of just around the area.
I'm thinking about using hamster chips. Thanks for any thoughts.
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