Allow your soil to dry out thoroughly. The larva can't survive but your plant will. If the adults are bad, buy some sticky fly traps or you could search for other homemade remedies to trap them.

I would also suggest either lessening how often you water or changing your soil medium if you keep seeing problems---the flies want and need moist soil to survive. Your plants want water too but they can last a while in the right potting mix without water. In other words, a dryer soil medium will stop the larva cycle and keep your plants happy too.

But can gnats hurt? I don't know for sure but I don't think so. The larva may harm new plants but established ones should be fine as with most plants. So really it comes down to whether or not you can stand the gnats?

Edit: I just read here elsewhere on Garden Web about using sand as a buffer. It stays dry so traps the larva and after about a week, no more gnats. It may be an easier fix than re-potting. I'll insert the link in post.

Hope this is of some help to you!

Here is a link that might be useful: Sand as a buffer.

This post was edited by ApacheRosePea00 on Mon, Jun 23, 14 at 14:28

You may want to question your potting medium, it could be too heavy and holding too much moisture, and there is also a chance you could be keeping it too moist. But if you have a heavy infestation, you're going to need some help other than changing cultural practices to get rid of them.
Get one of the BTi products and use it. Bacillus thuringiensis subspecies israelensis - nontoxic to mammals, birds, and fish, is specific to only mosquito larvae, and gnat larvae. Products may be Gnatrol, Knock out Gnats, others, and you can use mosquito dunks in a pinch if you don't find it in granular or liquid form. Drop a dunk in a container of water and let it sit over night, then use that water on your normal watering schedule, each time your water, for at least three weeks. It targets the larvae in the soil which must ingest it, and it takes a while to break the breeding cycle, but it does work so stay patient and consistent with the treatment.

Don't concern yourself too much with the adults you see, they live only a few days and cause no harm. The larvae in your potting soil are your target, and they do feed on fine roots. Particularly troublesome for seedlings, but they don't help the health of mature plants either. :)

One of our local television horticulturists has recommended the layer of sand too, it didn't work for me the month I brought them home in a new prayer plant from the hardware store and they went to every potted plant in my house. I watched them go in and out of the drainage holes in pot bottoms.

Thanks!! I'm going to DEFINATLEY change soils AND do the gnatrol product! I did notice when I watered the water wasn't draining out (I've only had this plant three to four weeks and have only watered twice) the bottom and it's pot has great drainage I think the soil is the biggest factor. Any ideas on soil? Ive ALWAYS loved plants but just recently decided to make it my hobbie so to speak and I want to make sure I'm doing the best for my plants. Thanks again for your help and advice. I also have a orchid I JUST got, no knats in that one but any tips on care would be greatly appreciated!!

There is a lot of myth and misinformation available about control of Fungus Gnats, and it is true the larva need a fairly moist media to grow in and allowing that to dry out is one means of control.
Perhaps the linked article might be of some help.

Here is a link that might be useful: About Fungus Gnats

Thanks!! I'm going to DEFINATLEY change soils AND do the gnatrol product

===>>> if you change the MEDIA ... then i dont know why you need to use a control....

and this can be left outdoors.. IN FULL SHADE... for the summer ... and gnats are NOT an issue.. outdoors.. usually anyway ...

it also roots.. in a glass of water... start a new one...

BTW... who diagnosed gnats???? we are taking your word.. that is the actual problem ... it probably is.. but if it isnt.. then all of the above... is useless info ...

ken in adrain mi

Lilbit, if you've just had the plant three weeks or so and have gnats, they were probably in it when you bought it. If you're planning on making a hobby of indoor plants, you'll want to inspect them very carefully before buying and bringing them home.

One of my sources for outdoor plants always seems to have the gnats in their indoor selection, I don't buy houseplants there unless I'm prepared to keep one in a separate room initially and treat.

Ken I saw the gnats flying around the plant and laying on the soil. So if I change the soil I shouldn't treat with gnatrol? I can take a clipping of my purple passion and it will root in water? Thanks EVERYONE for your help! :)