According to Herbs2000.com, celery grows wild around the Eurasian plains and in parts of England and Wales along marshland and coastal areas. Although it started out as a wild plant, celery has become a staple of many household gardens. Seeds, which are easy to harvest, are most commonly used as a condiment. The key to acquiring the best seeds, however, begins with growing healthy celery plants. Make sure to discard brown or wilting celery plants to avoid spreading disease to the remainder of your crop.
Plant a packet of celery seeds according to the packet instructions. Sprinkle the area with wood ash to increase the soil's potassium level, which will transfer to the celery as it grows. The soil must be rich, moist and receive 12 hours of sunlight a day. This will ensure healthy plants from which to harvest celery seed.
Grow the celery plant past when you would harvest it for food. Wait for the seed stalks to develop at the top of the celery plant. These stalks can grow up to 3 feet tall and will have green feathery flowers at the top; this is where the seeds are. Stop watering the planting area at this point.
Allow the stalks to dry out until they become brown and brittle, and cut them off with a knife.
Snap off the dried flowers over an old bedsheet, and tap the flowers lightly with a wooden spoon to get the seeds to drop onto the bedsheet. Discard the flowers.
Use a brush to sweep the celery seeds onto a clean dustpan. Use light strokes, as the seeds are very small and can blow away easily. Pour the celery seeds into a jar for storage.