Apium graveolens (celery and celeriac) is a member of the family Umbelliferae. Apiums produce flowers, called umbels.
Apiums have perfect flowers but, can not self-pollinate because the male anthers shed pollen before the female stigma is receptive. Therefore they cross-pollinate via insects (honeybees and other hairy insects) or by manually pollinating (hand-pollinating) the flowers in a controlled environment. Seed producers must keep in mind that varieties of the same species will cross-pollinate with other varieties of the same species.
Celery and celeriac are biennials (taking 2 seasons to produce seed). In severe climate the plants must be dug and stored in a root cellar. Celery should be trimmed back and stored in damp sawdust or sand with the tops exposed at 32 - 40 ?F with 90% humidity. In milder climates they can be overwintered in the ground. When planting apiums (or any cross pollinating crops) for seed, care must be taken to isolate same species varieties from one another, either through mechanical isolation (caging, bagging) or by distance isolation. In addition to isolating same species varieties, care must also be taken to preserve as much genetic diversity as possible by planting a minimum number of plants
Apium umbels need to be threshed first (we use a belt thresher but this can be done by hand threshing) and then the smaller chaff can be separated by using screens or an air column or simply by winnowing.