The Lesson of Peat and Fungal Gnats

In the midst of a small amount of rage, and as a bit of a public service announcement, I just wanted to share my new findings on pests which threaten the indoor urban gardener. Having recently tossed a young basil plant, soon followed by a young rosemary plant which I found withering and swarming with small flying insects, I did some further research. What I found was a too common species known as the Fungal Gnat. They're slightly smaller than your typical fruit fly and particularly enjoy potted plants.

Apparently the adult fungal gnat itself is not particularly harmful to plants, but their larvae are quite destructive. The gnats lay eggs in soil, particularly soil that is moist. They can lay hundreds of eggs which hatch quickly into larvae. The larvae thrive in the moist soil and attack plants at their roots for nutrients. On top of this, fungal gnats are known to spread diseases from other plants.

I've been annoyed by the flying insects because they were sticking around even after I had tossed all of the potted plants in my apartment, and throughly washed everything down. Granted there were only a couple here or there, but realizing they were not going away I started wondering both what they are and where they might be still living. Upon reading about the larvae in moist soils, I remembered that the large bag of potting soil I had bought (which I used when I repotted both the basil and the rosemary shortly before their downfall) was still loosely sealed under my kitchen sink. In my internet research readings I had seen warnings against using topsoil containing peat, which apparently these (and other pests) are particularly fond of.

Upon inspection, the bag of soil under my sink was teeming with several of the gnats around the opening. I picked the bag up, and quickly saw that the soil mix was one of peat moss with added nutrients for plants. I ended up tossing the entire bag of soil, and vowing never to return to the tiny hardware store up the street who had convinced me to buy the mixture..

So, that is my warning for anyone attempting to grow young plants - beware of soil mixtures containing peat, don't overwater, and act quickly if you ever see gnat like insects around your plants!

I'm starting out some cilantro from seeds in a different soil mixture this week, will see if the results prove better than the first try with herbs!