Question
I have had spider mites...dumped everything and started over...and now I have leaf miners. They must have come in on a pot of mint that summered on a friend's deck. Meanwhile, there have been apparently harmless little black gnats flying around during both infestations. Both the mint and a basil were grown from seed.

I'm willing to start over, but I want to prevent another infestation. Is it possible that eggs came in in a sealed plastic bag of potting soil?

I doubt that there is any systemic that i could use on kitchen herbs...but do you have any advice for a clean start and future prevention? These herbs are growing on an apartment  window sill over a macadam parking lot, so for sure nothing is flying in from a neighbor's garden.

Answer
Hi Jane,

Your instinct is correct - the pests are coming in the bagged potting soil you have been using. It is logical to assume that sealed bagged potting soil would be pest-free, but it is not. The most commonly available Miracle Gro potting mixes are notorious for harboring fungus gnat larvae. I use Pro-Mix and have never had any problems with it, but it is hard to find.

For seedlings, I recommend that you use a mix of plain peat moss with perlite mixed in - a ratio of 4 or 5 to one. This is a sterile soilless mix and is particularly good for seedlings that don't require many nutrients. Make sure you get rid of any existing plants that have fungus gnats as the winged adults will lay eggs in the sterile mix that you are using and contaminate it.

I have written an article on indoor plant pests that I will email for free to you (or anyone else) who emails 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