If you're going to put the DE into the soil, do it when you're going to have a few dry days, and don't water that area. DE is useless in the soil once it becomes wet. Could you grow your hibiscus in a container? I once had one growing in a large clay container and it did very well for several years, until I stupidly put some native soil in it that evidently had white grub eggs, and they ate all the roots.

I wouldn't mix it in, since moisture neutralizes its effectiveness. You might try sprinkling/dusting it over the soil surface, but that might only be good for a day, since morning dew would also render it ineffective.

I've tried mixing up insecticidal soap and using it as a soil drench, but can't guarantee results.

Soil dwellers that eat away at roots here are mainly grubs, wireworms and mole crickets. It's considered best practice to figure out what pest you're dealing with before trying to treat it.

All i can say is that it was alive and blomming one week and dead the next. I pulled out the roots and they were shot full with holes. Never saw the pest that made the holes.

Will crushed egg shells mixed in the soiled make pests avoid it?

From reading a bit about wet diatomaceous earth it seems wet only hurts it effectiveness while wet so once it drys back out again it work again so surface treatments works after dew has evaporated. But that won't help my soil problem but it does make my surface treatments between my neighbor's bedbugs and me reassuringly secure.

Eggshells will have no effect at all.

Unfortunately, there are some pests, especially those in the soil, and most especially grubs, that have to be treated with chemicals. I mostly garden using permaculture methods, and hate to use chemicals, but after almost losing my confederate rose (Hibiscus mutabilis) twice to whiteflies, I finally broke down and got some Bayer systemic insecticide. Using chemicals carefully and sparingly is not a bad thing. Its just unrestrained use of them on everything that damages the environment.

I’m so glad I read this thread! I have been wanting to mix in DE with my potting soil because I read an article saying that it helps with fungus gnats and mealy bugs. I heard people also ingest the food grade DE to clean out their system for whatever reason I’m not sure I forget. But anyways, if moisture kills the effects of it, I won’t waste my money! What a bummer I was hoping it would help. Darn!