Be wary of "free ranging" as a sole source of nutrition. Many people have the old, flawed notion that chickens can just fend for themselves. Turn them suckers loose and forget about them. To a degree this is so, but it is also lacking in a couple of crucial ways.
- forage foods are seasonal. In spring everything is green, jumping and yummy. But by summer things are picked over, dried out and toughened up.
- while chickens are out roaming, eyes are on them... Predators.
It's best to keep range foraging to a managed plot of sown plantings: deer forage, clover, vetch, greens beets, kale, etc. Rotate them around in a kind modified pasturing plan, and let them out to aimlessly roam under your supervision. Remain watchful for the preds.
Meanwhile, continue to feed them morning and evening, what they can clean up in 15 minutes. A feeding of dampened mash or grain as last meal will help them sleep, add weight and encourage them to get to roost at the end of the day.