I take it you've never had them run amok in your flower gardens? They'll peck & scratch the heck out of them. But certain flowers/plants can be toxic to chickens.
Here is a link to list of toxic plants, but I don't know if I agree with everything they have listed. Some things, like elderberries, are listed, but my girls eat them. I think the word "toxic" is a little overused & not explained as well as it could be. Some consider any plant that causes an unwanted body response (diarrhea, gas, etc.) as having a toxicity, but unless the reaction was extreme, it is by no means life-threatening. They have cabbage listed also, and that I do know causes a nearly life-threatening response in my gastrointestinal tract. Just ask my DH.![]()
http://www.poultryhelp.com/toxicplants.html
T.M.I. robin!!!
When you visit here I will not have any cabbage on site for fear of the bodily response...

