Celery and Celeriac grow under similar conditions (see below). Self-blanching varieties of celery have denser foliage than other varieties. If planted in blocks at nine inch intervals, the foliage is sufficient to blanch the stalks without any additional effort. Otherwise, tie stalks to blanch the hearts.
Celery can generally be harvested by the beginning of fall and if planted in blocks (not trench), it should all be lifted and stored before the first frost. It will stay fresh for several weeks in the refrigerator. Although it can be frozen, celery becomes mushy when thawed so is only used for flavoring in recipes. Dehydrating for winter use as a flavoring to sauces, soups and other dishes is an option.
Each packet contains 0.25 gram or approximately 230 seeds.
Cultivation: Start transplants indoors from February into April. Germination is affected by the interrelation of temperature and light. The seed will germinate with soil temperatures below 50F if the temperature is held constant and the seeds are in the dark. It will germinate at 70F if it is in diffused light and germinate in temperatures up to 85F if there is a 10-degree difference between day and night temperatures.
Cover the seeds lightly with potting media, keep moist, but not wet. Germination is very slow (sometimes up to three weeks) so be patient.
Set out plants when they are three to five inches tall in late spring after all danger of frost has passed. Space them twelve inches apart in rows twelve inches apart. Mulch to help maintain moisture. They are heavy feeders and like rich, well-drained soil, loaded with organic matter.
As with many root vegetables, celeriac is at its peak in the fall. Select roots that are somewhere about the size of a medium apple. Too small and there will be little to eat once peeled. Too large, and the flesh tends to be woody and dry.
In areas with mild climates, they should be allowed to remain in the garden and harvested as needed. In areas of harsher freezing weather, they should be harvested in the fall and stored in slightly moistened sand or sawdust in the root cellar like you store carrots. The roots will keep three to four months this way. If you are raising them to save seed, they are biennials and therefore flower the second year.