Well I did go out and measure my two, and 3.5-4ft is spot on. From bullbs, I've had them for 5 years.
I do recall reading in an old NALS yearbook (ca. 1963) about a certain strain that someone grew out east (New York?) that normally grew 6ft and perhaps more. The name "Virginalis" sticks in my mind, but really nave no idea if that is correct. I don't know if it still survives in horticulture now or not.
