I bought two packets of Delphinium seeds a while back; dwarf ones and tall ones. I never got many plants out of them but I did get a few. They flowered and I kept the seeds, planting them the following year, and after a couple of years of this I have a reasonable display. I have tried to keep the dwarf ones at the front and the tall ones at the back, but I'm not sure that there's much difference between them any more.
Slugs and snails love Delphiniums. If you are not careful, they will eat the emerging shoots in Springtime before you ever see them, so you have to put down slug pellets before you would think you have to.