Preheat oven to 350 degrees. Remove neck and giblets from turkey cavity; set aside. Rinse turkey inside and out under cold running water; pat dry with paper towels.
Stuff cavity of bird with celery, bay leaves, and half the carrots and onions; tie legs together with kitchen twine. Rub bird with butter; sprinkle with poultry seasoning. Season with salt and pepper.
Scatter remaining onion quarters and carrot pieces on bottom of a large roasting pan; add turkey neck. Place turkey on a roasting rack in the pan. Cook, basting frequently after the first hour, until bird is golden brown, thigh juices run clear when pierced, and an instant-read thermometer inserted into the thickest part of the breast (avoiding bone) registers 170 degrees, 2 1/2 to 3 hours. (If skin is browning too quickly, tent with foil.) Let rest 30 minutes before carving.