Spock hints that contrary to the common misconception that Vulcans have one and only one name, he has more than one name, like most humans, but when asked, all he says about it is: "You couldn't pronounce it."
The spores, in the early drafts, were a communal intelligence; when someone was possessed by them, that individual was granted telepathic abilities to link up with other possessed minds. The abilities of the spores to restore health were complete enough to enable them to return the dead to life. The antidotes for the spores were either the possession of a certain blood type or the introduction of alcohol into the affected person. Originally, Kirk leaped onto Spock and forced liquor down his throat to restore him to normal. In a surprise ending, the spores were revealed to be benevolent, conscious entities who never intended to act against anyone's will.
In Jerry Sohl's original draft (first titled "Power Play," then "The Way of The Spores"), it was Lt. Sulu who was infected by the spores and was able to fall in love with Leila. Displeased with D.C. Fontana's rewrite, Sohl was credited under the pseudonym Nathan Butler.
In the script, Kirk first spots Spock and Leila kissing passionately by the stream. There is no scene of Spock hanging off the tree limb. That facet of the episode may have been made up on the spot. Indeed, director Ralph Senensky came up with the idea of Spock hanging from the tree on location, when he found the tree and the spot closely to Bronson Canyon. Originally the scene was to be shot on a clearing. Evidence taken from a deleted scene, of Spock and Leila's presence near the stream, appears in the episode's preview trailer.
In a blooper, Leonard Nimoy flubs his line about the plants acting as a repository for thousands of spores. Instead, he says the plants act as a "suppository." The crew cracks up, as does Nimoy, who caps the fun by putting a Tootsie Pop in his mouth.
According to director Ralph Senensky, the original schedule was that the first three of the six shooting days were to be spent on location, shooting at the Golden Oak Ranch (also known as the Disney Ranch), then the remaining three days indoors, filming the Enterprise scenes. However, after two days of shooting outdoors, Jill Ireland fell ill and couldn't appear on the set. It was in question if she had measles or not. Senensky decided to film all the farm scenes which didn't contain Leila's character and then return to the studio for Enterprise interiors in the remaining of the day, and hope for the actress' return. Ireland appeared the following day, as it turned out that she did not have measles. However, the crew couldn't return to Disney Ranch as it was already booked for another production. They decided to film the remaining scenes at Bronson Canyon.
The empty shot of the bridge, before the turbolift opens to admit Kirk, was the best available piece of film for Star Trek: The Next Generation: Relics (1992) to reuse as the holosimulation of the NCC-1701 bridge. The short snippet of film was "looped" several times and bluescreened in behind James Doohan and Patrick Stewart's scenes. Using the stock footage in this way eliminated the need to completely rebuild the bridge - they only built a short section of the computer stations, the door alcove, and the command stations for the TNG-era actors to sit at.
Upon arrival, Sulu and another crewman inspect the colony for "whatever doesn't look right." Sulu says, "When it comes to farms, I wouldn't know what looked right or wrong if it were two feet from me." As he says this, the alien plant carrying the hypnotic spores is roughly two feet from him.
One of the basic aspects that D.C. Fontana immediately changed was Jerry Sohl's original conception of the spore plants residing in a cave. Thus, to avoid the danger of the plants, the crew merely had to avoid the cave. Fontana put the plants everywhere around the planet, and later the Enterprise to make them a real menace.
The food processors in the transporter room, placed there so Kyle could provide chicken soup for the air sergeant in Star Trek: Tomorrow Is Yesterday (1967), disappeared from the room by the end of the first season. In this episode, an enraged Spock destroys one of them.
Some of Spock's family background is fleshed out in the episode with references to his half human heritage. The episode also first reveals Spock's father being an Ambassador, which would be depicted in later stories. Spock's mother is said to be a teacher, but there would be no further details or depictions of such a career. However, Spock's mother and father are also referred to in the past tense, indicating they may not be alive (which is disproven when they appear in Star Trek: Journey to Babel (1967)).
The script featured characters named Lieutenant Timothy Fletcher and Crewman Dimont as members of the landing party. When Michael Barrier and Grant Woods were cast in these roles, the names were changed to DeSalle and Kelowitz respectively, to appear constant with the two actors' previous appearances on the series.
Originally Star Trek: The Devil in the Dark (1967) was scheduled to be filmed before this episode with Ralph Senensky directing it, and Joseph Pevney directing this one, but during pre-production the two episodes were switched, and changed directors. It was due to producer Gene Coon's assumption that "Devil" would be a tough assignment for a first-time Trek director.
According to D.C. Fontana, the episode had to be seriously rewritten because Jerry Sohl had not quite gotten it right. Gene Roddenberry told her, "If you can rewrite this script, you can be my story editor." She thought about it and eventually realized that the story wasn't really about Sulu, but about Mr. Spock. Leonard Nimoy, who was initially taken aback when he was told that they were working on a love story for Spock, later felt that the episode turned out to be a lovely story.
The buildings seen in the teaser, the first scene after and the scene in which DeSalle shows McCoy the Spores are at a different location than the buildings seen in the rest of the episode. The green farm structures were located at the Disney Ranch. The concept of Sandoval's people refusing modern technology was intended to justify the late-19th century Americano style of the ranch.
The large open meadow seen in several sequences is in Malibu State Park in southern California. It is the same spot where the hunt in the corn field took place in Planet of the Apes (1968), and also extensively used in Gunsmoke (1955).
There is a piece of equipment attached to the left side of the transporter console. It seems to serve no purpose, other than for Spock to hit when he misses Kirk during their brief dust-up, and was only seen in this episode. In fact, it was not in the scene where six crew members, under the influence of the spores, transport down. Similarly, the tray-like metal object that Spock is poised to throw on Kirk at the end of Act III is not seen in the transporter room in any other episode.
The trivia items below may give away important plot points.
This episode mentions several times that there are no insects on the planet. Without insects, especially bees, crops will not pollinate. And without pollination, crops will not grow. However, this being an alien world, other unknown processes of pollination can be assumed.
While recording his Captain's Log, Kirk stated that because the crew was in mutiny, they had effectively stranded him because he was unable to Pilot the Enterprise by himself. In Star Trek: The Mark of Gideon (1969) Kirk is the only member of the crew of the Enterprise still aboard (Kirk later discovers he's actually on a replica of the Enterprise). While on the Bridge with Odonna (a woman he found aboard while searching the ship) Kirk walks over to the Bridge Engineering Station and swaps out a micro tape from the computer at the station and puts another micro tape in the computer slot. Odonna asks Kirk what he had just done and Kirk says he just took the Enterprise out of Warp and activated the Impulse Engines. This indicates that Kirk can indeed pilot the Enterprise by himself with the assistance of the ships computer and pre-programmed micro tapes and creates a plot hole for "This Side of Paradise" because Kirk could have simply piloted the Enterprise by himself to the nearest Starbase and gotten help to recover his crew. However, it is possible that because of the events of "This Side of Paradise" He had the tapes programmed so that a single person could operate the ship.