Chickens, and many animals, are very adept at selecting the plants that carry whatever properties they need for health that day. That's why I include a mix of herbs in the daily feed during winter when they don't have access to them. Southernwood, wormwood, and tansy are all good for worming properties and one of these is always in the current mix.
Regarding mites, I've put the DE on the walls and floor of the nestboxes, and along the roosts. I make a mix of DE, LEACHED wood ashes, and soil for dustbathing. I've never had mites. I use LEACHED (ashes that have had water passed through them) because it the ashes get wet, they can burn skin and feathers. I've taken the tips off my fingers working wet unleached ashes.
Thank you @goldenoakfarm! Do you make leached ash yourself? I have never heard of that in our farming community. Although it would probably have another name (most likely Afrikaans). The chicken area is so big, that it takes a lot of DE and a lot of time.
It's not hard. I simply pile the wood ash from the wood stoves outside all winter, and then sift it in summer after it's sat in the rain for months. Then I store it in a dry place. It's not something you can buy.
My chicken pen is 800 sq. ft. and it does take a bit of time to spread it. Mostly I put it where they dust bathe the most, and in the nest boxes. I would not put the wood ash in the nest boxes, just the DE.
Thank you @goldenoakfarm!