I grew several plants outside this last summer Rosemary, Geranium, etc. When I brought them in for winter it seems I now have fungus gnats in all my houseplants. Please give advice. I would prefer not to use chemicals but am getting desperate.
Winter is a time that a lot of indoor plants become infested with fungus gnats. One of the primary reasons for this is that the soil stays too moist. I might suggest that you check the soil before watering to make sure the top inch is dry. The larvae of the fungus gnats live in the top half inch or so of moist soil so letting the planting medium dry out lessens the chance of infestation.
Now that there is an infestation you can try a few things including letting the soil dry out to help get the problem in check. Using yellow sticky traps in each pot will help catch some of the adults. This in not a true control but it will reduce the population of adults. Using Bti, Bacillus thurengiensis israeli, as a drench will kill the larvae. This is a biological control. It may be hard to find a product locally to use but I have seen Gnatrol sold on the internet. It has Bti as the ingredient. There are some other things that can be used to help in getting control. This UCANR publication on fungus gnats covers the options well.