That is such a coincidence that you're from Comfrey and you commented on planting comfrey for your chickens. A few days ago I e-mailed a bird farm and asked if they know of any plants other than clover that chickens like to eat. Just today I received a response and they said that chickens like to eat comfrey. I had never heard of it so i googled it and it returned the plant and the city (population 367)!
Thanks for the suggestion of millet and wheat.
I'm not sure what species of clover my chickens love, but it doesn't have the round flower like many species do. Rather the leaves of the clover are very small and there is usually only a few roots that support many (hundreds) of clover leafs. Once the weather warms up, I'll take a picture and ask for help identifying it.
My chickens love worms, so when I'm digging up the yard, they just go through the dirt and eat all of the worms in sight; it's pretty entertaining.