As filmed, this film included a sequence in which Wilma Dean Loomis takes a bath while arguing with her mother. The bickering finally becomes so intense that Wilma jumps out of the tub and runs nude down a hallway to her bedroom, where the camera cuts to a close-up of her bare legs kicking hysterically on the mattress. Both the Hollywood censors and the Catholic Legion Of Decency objected to the hallway scene, finding the bare backside unsuitable for public display. Consequently, director Elia Kazan dropped the piece, leaving an abrupt jump from tub to bed.
The film's title comes from the poem, "Ode: Intimations of Immortality" by William Wordsworth: "Though nothing can bring back the hour of splendour in the grass, / of glory in the flower, / we will grieve not, / rather find strength in what remains behind."
Jane Fonda wrote in her autobiography that she tested for the role of Deanie. When Elia Kazan asked her if she was ambitious, she replied "no" (even though she was) because "good girls aren't supposed to be ambitious." Fonda writes that she believes this was the reason for her not getting the role.
While a clip was not actually seen (though dialog is heard), there is a scene in Pedro Almodóvar's What Have I Done to Deserve This? in which the grandmother and her eldest grandson attend a showing of Splendour in the Grass. As they leave the theater, the poster (Spanish) is clearly seen in the background.
Incredibly - by today's standards - a Cedar Rapids, Iowa (USA) newspaper ad for this film says "No one under 16 will be admitted unless accompanied by an adult".
In the bath scene, Natalie Wood's wrist is very briefly revealed. She normally always wore a bulky bracelet or long sleeves to hide the protrusion of a bone in her wrist which she thought to be an ugly anomaly.
Even though they were supposed to be playing teenagers, Natalie Wood and Warren Beatty were approximately 22 and 23 respectively at the time of filming. As a result, Elia Kazan decided that the other actors who were to play teenagers in the film should be in their early to mid-twenties as a way to make it easier for the audience to accept Wood and Beatty as teenagers rather than as adults playing teens.
The nightclub owner played by Phyllis Diller is Texas Guinan, a real-life New York nightclub owner of the 1920's. "Hello, suckers!" was her standard nightly greeting to her nightclub patrons.
Although Elia Kazan had planned to film the movie in Kansas, a severe drought forced him to relocate all shooting to New York state. The waterfall in the film is located in High Falls, New York, in the Catskills.