Diatomaceous Earth as pest control for indoor plants

Factual Questions
1

I have converted a 55 gallon aquarium into an herb garden. The fungus gnats have converted it into a brothel. I want to slay the sinful creatures for they are naughty in my sight. I would prefer to effect my genocide with diatomaceous earth, but everything I’ve read says it doesn’t work when it gets wet. And of course, watering plants from time to time involves getting the soil wet. BUT…DE is basically shredded glass, eh? Seems like it would eventually dry out and resume its sharp laceratious quality.

My plan is to have about 3 inches of soil at the bottom of the rig, maybe 1/8 inch layer of DE, another inch or so of soil. That away when momma gnat burrows down to lay her eggses, she gets hacked up. And if any eggs do manage to get laid and hatch, the babby gnats will get shredded on their way to the surface.

Am I going to be wasting my time, or is my plan a cunning one?

2

In my experience, DE (diatomaceous earth) does not work. I have a 3 parts regime that does work and I’ll describe it below. Please note that this needs to be repeated every few (like 2 weeks) initially and then every month. These products are approved for organic gardening:

  1. BTI bacteria based granules or dunks or liquids. I use granules and put them in the watering can a day in advance (use chlorine free water or it will kill the BTI bacteria). Bti is EPA-registered for use in residential, commercial, and agricultural settings. Organic farming operations use Bti.
    Here is a link to Amazon but it is available at stores like Homedepot, Lowes, Walmart … https://www.amazon.com/Summit-116-12-Quick-Mosquito-8-Ounce/dp/B0001LE1VC/?th=1

Now BTI kills the larvae (the bacteria feeds on the larvae) but it is not effective on already hatched gnats.

  1. To kill the already hatched gnats, Spinosad works best. You just mix it with the water in your watering can. https://www.amazon.com/Monterey-LG6150-Garden-Spinosad-Concentrate/dp/B000BWY3OQ/

  2. Lastly you need a product that stops the gnats to fly to other plants in your house (if you have any). Yellow sticky traps work best for this and are available in most places. You can also use a bug zapper or mosquito zapper if you have one.

Good luck with your herbs.

3

I personally would favor Gnatrol (or another product that contains the BT specific for fungus gnats) over DE.

DE in my experience is messy to use and didn’t do a good job on the particular crawling bug it was supposed to kill (mealybugs).

4

It’s not shredded glass. It is a shredded rock which was, geologically, formed from the sediments of fossilised algae. Chemically, it is silica (silicium dioxide), which is used as the main resource used to make glass, but in a crystalline form (quartz).