The March/April issue of Chickens (Hobby Farms) has an article on safetly free ranging your chickens in your yard. A sidebar has a list of toxic plants. Most of these make sense...
Buckeye
Buttercup
Clover I knew I read years ago about White Sweet Clover (Melilotus alba, the tall shrubby clover, not the one in the lawn (Trifolium repens.) I get conflicting information, but one source ("Identifying and Harvesting Edible and Medicinal Plants (in Wild and Not So Wild Places)" by Steve Brill mentioned dicoumarin, a compound that is formed when coumarin, the vanilla scent present in M. alba, ferments. Googling "dicoumarin" I found a link to a UCLA web page that mentions dicoumarin (no mention of fermentation) and states that it is present in M. alba and caused scores of cattle deaths. I don't know how to print the link, but it was 3rd on the search results. Again, it did not mention fermentation, but it did confirm some of what I remember reading years ago.
Fireweed I'm curious how this got on the list? Fireweed is highly edible and sought after. But even our local wild edible guru, Arthur Lee Jacobsen, admits it can be "acrid" at times but that cooking alleviates it if it is a problem.
Foxglove
Ground Ivy I'm assuming this refers to Creeping Charlie, Glechoma (or Nepeta) hederacea, a mint relative.
Hemlock
Hemp
Hyacinth
Hydrangea
Japanese Yew
Jimson Weed
Kentucky Coffee Tree
Lantana
Larkspur
Lily-of-the-Valley
Lupine Carla Emery's chickens love the seeds, though, and she counted it as a protein source.
Milkweed
Purple Mint ?????
Nicker Tree
Nightshade
Ohio Buckeye
Oleander
Philodendron
Rhododendron
Rhubarb I also know of chickens who will eat this to the ground. Mine never touched it.
Saint-John's-wort
Sudan Grass
Tulip
But clover??? That's safe for human consumption, unlike all of the others. I've read several posts where members recommend giving clover to their chickens, and my front lawn is full of it during the summer. Can anyone clarify this for me?