The best solution I found last year was mosquito dunks soaked in your water. These contain a natural bacterial larveacide (bt). There is another product called "Mosquito Bits" that is the same stuff only ground so you can sprinkle it on the top of the soil.

It is slow going & will take several weeks for bt to work so if you already have a heavy infestation. You'll need to control the adults too. Yellow stick traps and some sprays are effective on the adults if you manage to spray directly on the gnat.

I also found that when the infestation got horribly bad (hundreds of larvae came up to the surface of the cups whenever I watered) that it saved a few of the seedlings if I repotted them, washing all the dirt away carefully before putting them in fresh soil. Transplant shock may kill some but the gnats will kill them all.

There is also a product called 'Gnatrol' that will kill the fungus gnat larvae, and with continued use will kill them all.
I use the mosquito dunks in water to water all my house plants. No gnats!
Ed

I also use mosquito dunks to water my house plants. I break a dunk in half and keep it in my watering pitcher. It takes a long time for it to completely dissolve.

For the adult gnats I found the yellow fly catcher tape to be very effective. It's messy and it's kinda gross...but it works.

I also keep a bottle of Schultz Houseplant and Garden Insect Spray on hand. It's organic and safe for inside use.
Good luck!

Kathy

Thank you all for the help. I tried to buy some mosquito dunks today at the local garden center but no luck. Is this something I need to order on-line? Does it look like little pills or what? I will also try to find the other things mentioned but today, no luck except did get some yellow sticky traps which I will put up immediately. But will keep trying. Thanks again. Makes me feel so bad as my babies had such a good start this year.

I bought my mosquito dunks at Lowes. They look sorta like a small donut. It says -
Summit Mosquito Dunks
6-Pack Mosquito DUNKS
Item #: 92460 Model: MODU1
$9.47
I'll post a link for you.
Kathy

Here is a link that might be useful: mosquito dunk at Lowes

Kathy, thank you so much for the info on where to purchase mosquito dunks. I have looked at several garden centers and no luck. I live about an hour from the nearest Lowe's store so will get as soon as a chance. Meanwhile, guess I will just lose lots of my babies. But, next year will be prepared. Thanks again. Libby

Libby,
You should call the Lowe's before going. As I recall, the dunks are not available in all states.
Ed

Libby, You could also try Ebay. I've seen them for sale there. It might be more convenient.
Kathy