The normal celery, of which the leaves are used, is sown in spring in March and later again in September. I usually sow in pots and plant them out later. You can also mix the seeds with moist sand and let them start to germinate before sowing outside. In September you can sow in pots or under glass. You can actually sow through the entire summer, but the plants won't become as big as those sown in March.
Spring celery can be harvested in August-September. Autumn celery from February to April. Cut or pick leaf celery when they are about 15 cm high, but don't cut out the heart so you can harvest again.
Celery root can be pre-sown from February to April and planted out in May and June. Celery root needs longer time to grow and likes a fertile soil.
In the past, celery was grown as a vegetable for winter and early spring. It was perceived as a cleansing tonic. It is used in some weight-loss diets where it provides low-calorie fibers.
Celery is also grown for its seeds. The volatile oil is used in the perfume and pharmaceutical industries. Celery seeds, whole or ground, can be used to season dishes.
Celery plants in a cold frame. These plants were sown in the summer and had little difficulty to withstand freezing in winter.