I often toss celery to ours. We get a lot of it as grocery store "culls". The girlies really seem like it- it disappears faster than some other things.
I feed it in moderation though. It does have helpful vitamins A/C/K/B6 and potassium, riboflavin (B2), and phosphorus. But it's also on the salty side...chickens cannot handle high sodium levels.
Celery has no protein content either. So be aware it will reduce the total average protein intake for your girls when you feed it. Again....small amounts.
Thanks guys didnt see celery on the treat list and wanted to make sure it wouldnt hurt them. i get cull celery too from the local gas station so thought it would be nice.