This is issue 97 of Cracked from November 1971.
I've been posting issues out of order and they've reprinted articles many different times, so I won't always remember what I've put here before. I'll try to when I can, so forgive me if you see something twice.
Here's their cover by John Severin as described on the contents page thusly:
Sylvester was really down in the dumps the other day—felt like it had become such a lousy world, life wasn't worth living anymore. Then he found that flower growing up through the sidewalk and it renewed his faith. He was a changed janitor, and for once he was even willing to empty the wastebaskets! It was a nice change, but frankly, were getting a little tired of the whole deal. It was one thing to water it, but keeping tons of fertilizer for it around the office is something else again!
psychedelic posters, on the inside front and back covers, and again by John Severin to accompany the article inside (which you'll see eventually)
Also on from the contents page:
In the beginning, psychedelic posters were great. But like most good things, they were seized upon and exploited for every penny they're worth. There's nothing worse than a psychedelic deodorant advertisement. So, we figured that enough's enough, and decided to retaliate with a psychedelic poster to end all psychedelic posters.
Exploiting the psychedelia craze? Seems they were the pot to Cracked's kettle. Like other Mad-influenced humor magazines, they were a few years behind the times too, but better late than never.
Escape From the Planet of the Apes. Mad didn't parody each movie in the series individually, saving everything for a longer article.
Vic Martin did for them.