Winter rye is aptly named. It is just so dang hardy. You can sow it in September, or even later. It will grow a little and then stand there and stay green all winter, holding your soil in place and protecting it from winter rains, compaction, and erosion. Then, in March, it will grow some more. A month before you want to plant in the bed, mow it down, pull it out and compost it, or broad fork the bed and flip the clumps up so the roots die. Winter rye is at its most nutritious (both as chicken forage and as mowing down and chopping up as soil food) at no more than 6" - 8" tall.
The beds I planted in winter rye in October have offered greens for cutting for the chickens all winter, and especially now, before much else is green. I plan to cut all the beds I have planted in rye for chicken greens over the next week or two, a different section each day. I hand harvest it so I can snip it up for them as it isn't good to give chickens long grass. Sounds labor intensive I know, but it goes quickly.