Celery seed is usually started indoors about 10 weeks before it is time to set the plants outdoors - that is, after the soil is warm and the air temperature settled. The seed is minute and finicky, and is started in much the same manner as African violet seed, in closed containers to keep seedlings moist. Soak seeds overnight to help germination. Transplant seedlings (see: Guide to Transplanting Your Seedlings) outside when they are 4-6 inches tall and night temperatures don't fall below 40F. Water plants before they are transplanted. Plant in rows 2 feet apart; with 6 - 8 inches between plants. How to Grow Organic Celery from Seed »