While it is uncertain who designed Juran, Akira Sasaki known for his involvement in the kaiju sculpting including the original Ultraman and Ultraseven masks says in a book interview it should be Yasuyuki Inoue, Toho Special Art Division, who designed the flower monster.
Sasaki says, when he joined the crew members for the first time at the Tokyo Bijutsu (art) Center (abbreviated as Bisen), Inoue brought the design to him and asked him to sculpt it.
After thinking about what it should be made of, Sasaki says he decided to sculpt it with styrofoam.
Sasaki recalls he made the male and female molds of the flower part of the monster and, by heating the molds, he cast the parts by pressing a sheet of styrofoam 5 mm thick between the molds to sculpt the monster flower in two different sizes.
He says a petal of the larger Juran measured about 1 meters, and it melted away excellently when thinner was sprayed over the flower.
While he says he worked on the sculpting at the Bisen as he was offered a room about 66 square meters for his own use there, he laughs he remembers the sloping floor with nostalgia as the studio was like a shanty without any air conditioning.
For the scenes in which Juran’s giant root was found in the castle ditch, a life-sized prop was used as it was shot in a giant pool of Toho,and optical compositing was applied to the scenes with the root floating in the ditch.
It is said that, in the scenes of Juran coming into bloom, the petals were initially manipulated by wire but they were eventually retaken in stop motion as the scenes with the wire manipulation did not satisfy Eiji Tsuburaya and he rejected them.
It is known that Satoshi Furuya, original Ultraman actor, is found among the onlookers watching the giant root with his line “Don’t shove!”