Question
Hello Will!

I have noticed over the past several weeks little black bugs on the dirt of a houseplant of mine.  The bugs can fly as they do this when I am watering them.  They do not seem to be eating the plant as there are no visible holes in the leaves, stem, etc.

The plants that I have seen most affected I have been told are called "a wandering Jew" plant.  

I got the stems from a friend and grew roots by placing them in a cup of water.  I then after they had roots put them in new fresh miracle grow dirt I purchased from Walmart.  

How do I get rid of the bugs?  Also, what caused them?

Answer
Hi Fred,

The bugs are fungus gnats. The gnat larvae (eggs) were in the soil that you used. I have received numerous complaints about this problem from people who use Miracle-gro potting soil.

The gnat larvae thrive in moist decaying organic material, such as potting soil. As they mature, they develop wings and then fly off from the surface of the soil. The flying adults live for about a week before they die on their own. The key to eradicating these critters is to treat the larvae in the soil, not the annoying adults in the air.

Most of the larvae live in the top 2 inches of the soil. So, first remove and discard all surface soil that is not in direct contact with the roots. That will eliminate a good portion of the larvae. Then allow the top quarter of the soil to dry out before watering. This drying out process will deprive most of the remaining larvae of the moisture they need to survive. The reduced watering will also help the roots of your plant grow stronger. If necessary, you can spread a thin layer of sharp sand over the surface of the soil. The sharp edges of the sand particles will carve up any larvae that try to move to the surface.

I have written an article on indoor plant pests, including fungus gnats, that I will email for free to you (or anyone else) who sends a request to me at [email protected].

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

Visit my website at: A link to HorticulturalHelp.com