I have grown these as annuals here in zone 5. They love full sun, deep loamy garden soil and plenty of water. They grow very well in pots; their root systems are thick and large. The bigger the pot the bigger the plant will get. They germinate quickly and transplant easily as long as they are small. They are easy to collect the seeds from and they can sow themselves. Good Luck!
As I remember, they germinate best when just pushed into the soil to make contact and not buried in the soil.They need light to germinate. Also, you can pinch off a lot of the leaves in the long stem so that the flowers are more easily seen. Wait until the flowers appear and then pinch off the leaves that are hiding the flowers. It makes them a lot prettier.
These are one of my favorites.