C'mon, surely someone here has an answer. Is it alright to add Foxglove, etc to our compost piles? My guess is yes, since it would break down, just like weeds do. However, I've heard that you should never add Walnut leaves to compost because the tannic acid (or whatever it is that prevents things from growing) doesn't break down.
All greenwaste from your garden, including plants listed as poisonous are fine unless the toxin is considered persistent in soils. The microbes that decompose organic matter don't have the organs that digitalis affects. I've always thought our compost piles had heart but I've never seen a compost pile die from heart failure...lol.
Creosote bush and other plants rich in essential or non-volatile oils might pose a problem if they comprise a large percentage of the organic matter in a pile.
Yes it is true that earthworms have several hearts but they are not affected by digitalis in that their hearts pump through a different mechanism than ours.