Place ham in a very large stock pot; cover with cold water. Bring to a boil. Reduce heat, and simmer 20 minutes. Drain; cool ham slightly. Remove skin and fat from ham, and discard.
Combine spinach, greens, celery, onion, and chives. Cover with boiling water; let stand 5 to 10 minutes. Drain well, and rinse in cold water. Drain well. Add celery seeds, pepper, and hot sauce to spinach mixture, mixing well. Set aside.
Starting at butt end of ham, make a row of lengthwise slits, 2 inches long, completely through ham. Repeat rows over entire top of ham, making sure slits do not cut into other slits. Pack spinach mixture into slits. Place excess spinach mixture on top of ham.
Wrap stuffed ham in cheesecloth; tie ends with string. Place ham in a large stock pot; cover with water. Bring water to a boil. Reduce heat, and simmer 2 1/2 to 3 hours.
Remove stock pot from heat; set aside. Allow ham to cool 2 hours in cooking liquid. Remove ham, and discard liquid. Allow ham to cool to room temperature. Chill overnight. Remove cheesecloth
Transfer ham to a serving platter. Cut diagonally across the grain into thin slices to serve.
Note: Leftover ham maybe refrigerated for later use.