Yellow-green stalks without string, which can be eaten raw as well as cooked. Sow directly in the garden from late March to early July. Emergence can be accelerated through germination in a greenhouse, then prick out the plants in pots or soil blocks, and allow to harden off. Transplant to soil with good water retention. Harvest before frost starts. Celery has diuretic powers, is low in calories and very rich in vitamins.