Thanks for doing the research Foxy, I knew I had read recently that Tansy can be toxic to humans but cannot remember the context.
I am a great believer in using natural substances where possible but do have concerns about depending on old texts and tales. A lot of what was used in the "ancient world" is fine but more recent (ie mediaeval onwards)ideas can be downright dangerous - using arsenic and white lead as cosmetics for instance. I also think some more recent texts can work on the basis of "if a little is good, more must be better" which is by no means always true.
The list in herbcottage is interesting but they don't give quantities to add to feed plus, according to Wiki, different compounds are at different strengths during the growth of the plant, which could affect the toxicity to hens.
The idea of a herb garden for the chooks is quite appealing, but can one really trust them to eat only what they need and not overdose? Humans (including me) can't do that but maybe hens are more intelligent!!
although it does sound like it wont work overnight so only time is going to tell .
