Avatar for Kman1983
Mar 14, 2018 8:08 AM CST
Thread OP

Hi All,

I need some help with gnats in my house plant (its a croton). I've had a the plant a very long time from when it was a foot tall to several feet tall now. I've kept up with repotting and have never really had any issues until this year when it has developed a fungus gnat problem. I noticed this a few months after the most recent re-pot so it may have originated from the new soil. I also think I may have over watered and the larger pot seems to really hold moisture for a loooong time.

In any case I tried treating it with Hydrogen peroxide mix, I removed the top layer (2 in or so) of soil and replaced with gravel. I thought my problems were gone but now I'm noticing larvae at the bottom in the drain holes. Not a lot mind you but I had zero before. The plant seems healthy all the leaves are green and normal. I'm thinking I just need to completely re-pot the plant with fresh soil? And also rinse the roots really well? The soil at the bottom of the pot is still very wet so if I do re-pot I need to consider a different drainage strategy I think.


Mar 14, 2018 10:30 AM CST
Name: Tommy
Hudson Valley of N.Y.
Buy a package of "Mosquito dunks" at the garden center. Put one quarter of one in your watering can. This will kill the larvae in the soil and stop future generations. It is all natural and safe. Use sticky traps and manually kill the adults.
Mar 14, 2018 3:31 PM CST
Name: Will Creed
Prof. plant consultant & educator
It is unlikely that your Croton needed it's most recent repotting. It should not be in a pot that takes a "loooong " time to dry out. It is during that extended time that the roots are deprived of oxygen and start to decay, further feeding the gnat larvae and ultimately killing the roots system and the plant. It is good that you removed the loose soil from the surface, but a mistake to replace it with gravel that will maintain the moisture level that the larvae are enjoying. Peroxide has no effect on the larvae and also just adds to the moisture level.

I suggest that you undo the repotting, but only if the rootball is still intact so that you can easily remove just the contaminated soil that you added and then move it back into its previous pot.

NEVER, under any circumstances, remove all or most of the soil as that will not only remove the gnat larvae but also damage most of the root system and probably kill the plant.

The only drainage strategy you need is a pot that is not too large and has a drain hole and a potting mix that incorporates lots of perlite so the potting mix is porous and dries out appropriately about once per week.
Will Creed
Horticultural Help, NYC
Contact me directly at [email protected]
I now have a book available on indoor plant care
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