Cultivar unknown. Celery is a mainstay flavouring vegetable as well as popular snack vegetable. With regular watering and weeding, celery is fairly easy to grow. Celery seeds need warm temperatures to germinate and a long growing season, so it’s best to sow indoors to get them off to a strong, early start in March-April. They should then be transplanted outdoors after the last frost, into rich, damp soil.