“My fake plants died because I forgot to pretend to water them” is a jocular one-line saying that has been printed on many images. American stand-up comic Mitch Hedberg (1968-2005) used the line in his act by at least 2001.
 
 
Wikiquote: Mitch Hedberg
Mitch Hedberg (24 February 1968 – 30 March 2005) was an American stand-up comic known for his odd subject matter, subdued delivery and memorable routines that often consisted of a string of one-line non sequiturs.
(...)
Mitch All Together (2003)
. My fake plants died because I did not pretend to water them.
   
Google Books
How to Be Funny:
The Ultimate Guide to Making Funny Speeches
By Ethan James
BookBaby
2001
Pg. ?:
Mitch Hedberg
On having a green thumb: “My fake plants died because I did not pretend to water them.”
   
Twitter
Rob
‏@wyldeMann
my fake plants died today because I did not pretend to water them.
8:57 AM - 7 May 2007
 
Twitter
Daniel Voyles
‏@DanVoyles
My fake plants died. I didn’t pretend to water them.
5:52 PM - 22 Jan 2008
 
Google Books
Dim Wit:
The Stupidest Quotes of All Time
By Rosemarie Jarski
Berkeley, CA: Ulysses Press
2009
Pg. 210:
My fake plants died because I did not pretend to water them.
Mitch Hedberg
 
Twitter
Jeramey Jannene
‏@compujeramey
@joshjs Mitch Hedberg jokes were designed to be twittered.. my fake plants died.. because I forgot to pretend to water them.
2:36 PM - 29 Jan 2008
   
Google Groups: uk.food+drink.misc
Re: OT Apple computers
Mike.. . . .
10/25/11
(...)
I had some artificial flowers, but they died when I forgot to pretend to water them.
 
Google Books
The Mammoth Book of One-Liners
Edited by Geoff Tibballs
London: Constable & Robinson Ltd
2012
Pg. ?:
My fake plants died because I forgot to pretend to water them.
 
Google Books
The Everything Big Book of Jokes:
Hundreds of the Shortest, Longest, Silliest, Smartest, Most Hilarious Jokes You’ve Never Heard!
By Evan C. Thomas
Avon, MA: Adams Media
2014
Pg. 247:
“My fake plants died because I did not pretend to water them.”— Mitch Hedberg