@Rockhead,
I've used Epsom Salt for years on roses, peppers and tomatoes. I think it works, especially on roses that have suffered winter damage.
There are so many myths and old wive tales that I wouldn't know where to start. The one that recently got my hackles up was on a homesteading website in which a woman (a woman mind you!) said she never works in her garden when she has her menstrual cycle because it poorly effects the plants. Although totally challenged by other posters she would not see reason. This was not the first time I've heard such a thing.
I think much of companion planting is untested science. While certain plants like to be together due to liking the same conditions, they do not help one another grow. Jewelweed does not grow near poison ivy because it is a cure. They grow together because they both like moist shade. I keep daring believers to give themselves a case of poison ivy and then clear it up with Jewelweed, so far no takers.
The whole marigold, tansy, mint (fill in the blank) keeping pests away is a myth IMHO. It does help to grow pollen laden perennials near a vegetable garden because they attract things like parasitic wasps, but plants do not keep away insects. Citronella does nothing to keep away mosquitoes.There are substances from plants that can be distilled and used as insecticides, but that is not the same thing to me.
I think organic practices are excellent, but bio-dynamic has no supporting science and is all hearsay. People totally confuse the two.