Usually grown as a fresh, munching vegetable, celery is used in our house mostly as a flavourful herb. Leaves and stalks are harvested and chopped up for soups and stews, and tossed fresh into freezer bags for "fresh" herbs through the winter.
Celeriac is simply celery that has been bred to grow a large root and few leaves, making a lovely winter storage vegetable that adds celery-flavour to cooking.
Celery and celeriac are umbelliferae (botanical siblings to carrots, dill, Queen Anne’s Lace, and the like). Start seeds early indoors (approx. 10 weeks before planting out), as celery is a relatively slow germinator. Prefers cool and moist growing conditions; transplant about 2-3 weeks before last spring frost.