I'm definately no expert but I think you'll find Sunflowers have a long "tap root" so planting in a pot is not so good.Wait until all chance of frost is gone then put your seeds straight in to good rich soil.When they come up try to water around the plant not on it,and when they get bigger stake them well ,I've used bean sticks in the past.Make a little"moat "around each plant and water into it.They like lots of food if you want them to be huge.The flower heads can get very heavy so tie the plants well right up the length of the stem.Even if yours doesn't get very tall the birds will love you for the seeds. Hope anybody interested can understand this ,seems a bit garbled to me ,sorry.
