This is the perfect time of year while you are outside mowing the lawn, and picking weeds to think of your chickens, save the clipping, and weeds throw it into the run and they will have a party, it will also keep them busy for a few hours. Their are actually benefits with dome of the weeds for chickens.
I fertilize the front lawn of my house so it looks nice, and parts of the back yard, but the section where I sometimes let my chickens out supervised, is where I do not fertilize. And the reason for that is they love the grass and weeds, so I let them out while we clean the coop and they love it, chickweed is their favorite. Chickweed was originally so named because chickens loved them so much. Chickweed is also a natural pain reliever. And they go crazy for it, it is actually funny see.
Certain weeds like pennycress and alfalfa contain the compounds that make your egg yolks bright orange, and some Clover is one of the most nutritiously complete weeds you could feed your chickens. Yarrow is common almost everywhere and while the chickens probably won't eat it, it has lots of antibacterial properties and hanging yarrow in the coop can help clear their respiratory systems. I cleaned the weeds out of the garden yesterday and dumped an entire bucket of grass and weeds in their run, and it was a sight to see, each chicken picked the weed of choice, ran in circles so no one could get it, and found a spot and enjoyed it. As an added bonus, most weeds are extremely nutritious and contain tons of vitamins, minerals and other nutrients. Winter weeds are especially good healthy treats when grass and other greens are scarce. There are long lists of toxic plants and weeds to avoid, but for the most part, chickens will know what they can eat and what they can't. Most of the common yard weeds are fine, except for the Buttercup (Ranunculus spp). It causes mouth and stomach irritation and can be toxic in large enough amounts, so avoid letting your chickens near any wild buttercup.