I've just potted up a cutting from this year's now-deceased salvia plant (planted in the ground, and claimed by frost).

I've always had problems with fungus gnats invading my potted plants in the past, and am desperate to avoid that happening again. The wider web has little to say on the subject other than chemicals...

This year, I'm using a blend of ericaceous compost, perlite, coir and worm-casts, with a mulch of tea-leaves, to simulate forest-floor leaf-litter, and hopefully keep the pH low enough to dissuade the little blighters from moving in.

But if anybody has any better ideas, I'm all ears!

Thanks in advance.

The best anti-gnat solution I've used during mushroom grows is an apple cider vinegar trap and I never had any trouble with gnats infesting my mushies:

"Make a homemade gnat trap. One easy way to rid yourself of a gnat infestation is with an easy and cheap do-it-yourself gnat trap. Find a used can or jar (Mason jars work especially well) and fill it with apple cider vinegar. Gnats are extremely attracted to the scent of vinegar. After you fill your can or jar, seal the lid and poke very small holes with a nail or screw. Leave the jar in a space gnats usually inhabit, most likely your kitchen or dining area. You can make several of these jars to leave in multiple locations, if necessary.
The gnats will fly into the jar, but will be unable to leave. Once the jar becomes full of gnats and you no longer notice any flying around, dispose of the jar and say goodbye to your gnat problem.
If you don't have apple cider vinegar on hand, any type of vinegar will do. Regular white vinegar works well, though you may want to add a couple of drops of dish soap (preferably lemon-scented) to the jar to make it more appealing to the gnats. Another alternative is to chop up a little banana or leave some banana peel in the jar.
If you don't have any lidded jars available, you can make another kind of trap by cutting off the top third of a soda bottle and placing it upside down in the rest of the bottle to form a funnel. Tape it to secure.[1]"

From here: http://www.wikihow.com/Get-Rid-of-Gnats

Hope this helps!

microwaving yer soil before potting ya plants indoors will kill off any unhatched critters. The problem is bagged soil & mulch from large scale stores can have major infestations waiting to come and eat up ya plants. I dont own a microwave so i cannot personally say this is a foolproof method.

Ive never had much luck with diatomaceous earth & and the vinegar/wine traps do work well but also buy a stack of those "yellow sticky traps". The yellow traps work amazing and have saved a many indoor salvia plants.

if you can put your plants outdoors during the growing season, nature will keep those bloodsuckers in order and if your plants are healthy enough hey will withstand any indoor attacks wih these 2 methods.

Thanks T, I was hoping you might chime in with some of your expertise...!

I haven't tried microwaving compost, but I have freeze/thawed it, and that didn't seem to help. Tried to find diatomaceous earth here, but couldn't...guess I didn't miss out on much, then. And already have plenty of sticky traps, with which to taunt myself as they change from yellow to black...

So, I'm most grateful to The Grateful One, looks like vinegar traps ahoy, then! That also indirectly explains why maybe it wasn't such a good idea in the past to add the odd splash of kombucha to the watering-can...

Iv noticed that a nice 2 or 3 inch thick layer of perlite seems to keep gnats from being able to burro into the soil to lay eggs and also seems to keep any larvae that hatch on the perlite from being close enough to the nutrients (soil and roots) to stay alive, I would use this in conjuction with a wet trap as mentioned above, even a cup plain water will do, they will fly into the cup and drown in the water.

If your a coffee drinker, one supportive tactic is this. After brewing a cup for you brew a whole pot of water through the used grounds. Pour this piss weak coffee into a deep tray or pie pan.
It wont kill them all but it helps keep the population lower. When fungus gnats smell coffee they just dive in and drown. I think theyre from seattle