Gnats in the soil

[jimmylove]

So somehow I got a fungus gnat infestation. Removed the pot from Scooby's cage, removed the plants (3 schefflera trees) from the pot, washed them and planted them outside so they can try to heal (had to cut the roots off of two of them, so its not looking good). Sucked up most of the gnats in the cage with the vacuum cleaner, slowly getting the rest of them. My question is about the soil in the pot (Miracle Grow organic from Home Depot, which I'm reading is a major source of gnats... wish I knew that in the beginning). It seems like a shame to dump all that good soil. Is there any way I can still use it? If I leave it outside in the sun for like 30 days and let it dry out, will it be safe to use again? And any advice about what to do to prevent the little buggers from coming back next time? My thinking right now is to mix sand with the new soil (1/2 and 1/2) to increase drainage, and put a 1" layer of sand on top. I've been reading that the gnats can't dig through that sand layer. I've also read that a 1/2" of diatomaceous earth on top will kill them as well. What are your thoughts?

 

[RAP66]

Common problem with cresties.... The common suggestion is to let the soil dry out more. I've also read that you can help control them with a jar of soapy water. I've never tried it so i can't sy how effective that is.

 

[Chameleonmaster]

I had a white fly problem and I tried the soapy water and it doesn't work. I think just let it sit in the sun and wait a month and see what happens.

 

[sulfurboy1o3]

Do they appear to have dark bodies and light wings?
These are probably fungus gnats. google them for photos.
do what Rap66 said and let the soil dry out.

Once you have an infestation it usually wont be long until your plants starts to look weak.
When you do resoil you next plants, use a sandy soil mix with much sand on top. cover that with rocks if you must. The sand dries out faster and makes it more uncomfortable for them to lay.

 

[sandrachameleon]

yes, let the soil dry completely out in the sun, bone dry, and you'll stop the gnat cycle. Baking in oven will do the same thing maybe faster.

next time, cover the soil with a piece of landscape cloth, and cover that with at least an inch of river rock. The flies wont be able to lay eggs in the damp soil because of the barrier. Good idea to let the soil dry out now and then anyways. If you are getting gnats, it means there is likely fungus (which the larva eat) growing on your plants roots being too wet.

 

[jimmylove]

There was definitely a white fungus in the soil. I didn't think much of it at first, until all the gnats started popping up. And the soap/water (I used apple cider vinegar) doesn't work (thats for fruitflies... these gnats aren't attracted to it).

The schefflera trees are planted outside now (I'm in Cali, so the weather is fine for them). Hopefully they recover while the soil bakes in the sun for a while. The landscape cloth for next time is definitely a good idea too.