I started mine in the ground where it would stay for the season. I would give it some room say one plant for a 6" pot if it will stay in the pot all season. I was suprised at the root system of my plants. If your growing more than one container, try it both ways, one here, two there. Keep the late West sun off of them, it makes them wilt. Enjoy!- millie

I am zone 6 in MA. THe cilantro likes the cooler weather. Too hot and it will bolt. You should also try succession planting so you have a continuous supply.

Stargazer's method works best. Cilantro will regrow ferny and be more bitter after the first cuttings so it's best to replant every 3 weeks throughout the year. Seed is cheap and so I'd plant thick (1/8" spacing or less).

You could even plant in blotches (small circles) if you don't use much. In a 6" pot arbitrarily divide into quarters. Sow ~20-25 seeds in a 1 1/2" circle in one quadrant. Three weeks later repeat with an adjacent quadrant, etc. That pot should be good for most of the summer but since cilantro keeps growing after frost, start a second pot for fall. You could be harvesting into December.