According to Preserving Foods by Oxmoor House, "Discard woody stems. Was, sort according to size, cut into lengths to fit container, or cut into 2" lengths. Blanch (small stalks, 2 min; med. stalks, 3 min.; large stalks, 4 min), cool, and pack into containers, leave no headspace. Alternate tips and stem ends in containers. Seal, label, and freeze."
I would do it like that but I would freeze in freezer zip-top storage bags.