I got in 18 Australorps a month ago which were already a couple of months old. Five of them were about 4 mos old. I constructed a chicken tractor and put the older ones in, which I placed in the walking rows between my vegetable plantings. I have a 30 member organic CSA for vegetables and am adding eggs once I have enough chickens of the appropriate age.
The primary reason I got the chickens, however, is weeding. I also have Tennessee Fainting goats for the same reason.
The chickens were initially a bit confused and it took them a week to eat down the grass in the tractor, so I discontinued using a feeding tray and now just throw the feed directly on the ground, along with some grit. They are doing better with it and I am able to move the tractor in about four days.
Meanwhile, the grass in the regular coop run is totally gone and I have put down pine wood chips. There is also a goose in there which has helped a lot with the grass removal. It used to be an unused dog kennel where I had to go in with a weed wacker. Now I'll never wack in there again!
Once they have finished weeding the walking path, I will still have to over it with a small rototiller as they don't dig up the roots so everything will just come back. The loosend dirt can then be thrown onto the beds with the plants to fertilize. What a system!