are delphinium perennial
Rating Newest Oldest. Best Answer: There are both annual and perennial members of this tall and showy, flower family. With many vanities in this family, Delphinium range in size from about one foot to several feet. ****Caution: All parts of Delphinium are poisonous and could be fatal. Delphiniums are beautiful perennial plants, very hardy and reliable - I've had both light blue and dark blue varieties for a number of years. If well tended and fed properly, they will grow taller and fill out each year, so you can split them and plant up the division elsewhere.