Datura Belle Blanche (megahuge blooms 8" across) This one is perennial from zone 6-9
Soaking the seeds overnight in hand-hot water is often beneficial. Sow the seeds in a good soil mix, and barely cover them with soil. Mist the soil heavily, and cover the container with a clear plastic dome. (A sheet of clear plastic will work, but an actual dome is better. Place the seed tray in good light, and if bottom heat is available it will be helpful. Check often, to be certain that your soil doesn't dry out. If there's condensation on your dome, it's plenty wet, Don't water again until this clears up, because too wet seeds can rot or develope fungal diseases.