DC Comics writer Leo Dorfman wrote many of Superboy's adventures back in the 60's, and thus also wrote a number of the Teen of Steel's TV shorts as well.
In "Superboy's Super Dilemma", Superboy (Bob Hastings) is given a serum by Professor Potter (Ted Knight, who also narrated) that is meant to make him immune to Kryptonite, but the befuddled scientist mixed a plant growth formula with the serum, causing Superboy to grow to gigantic proportions.
It might work better on the printed page, to tell you the truth.
What I find befuddling is how Superboy couldn't figure out for himself the cause of his sudden spurt. The viewers, I'm sure, had it figured out in mere seconds.