“I used to have a rock garden—they all died” is a classic joke. Rocks don’t die like plants do, of course. The joke is that the speaker is a very poor gardener.
   
“I once had a rock garden but they all died” was posted on the newsgroup alt.vampyres on February 11, 1995. “I used to have a rock garden—they all died” was posted on on the newsgroup alt.alien.research on January 16, 1998. “Does this old joke sound like you? ‘I am such a bad gardener. I once planted a rock garden, but they all died’” was written by “Greener View Gardening” newspaper columnist Jeff Rugg on June 1, 2022. Authorship of the joke is unknown.
   
           
Wikipedia: Rock garden
A rock garden, also known as a rockery and formerly as a rockwork, is a garden, or more often a part of a garden, with a landscaping framework of rocks, stones, and gravel, with planting appropriate to this setting. Usually these are small Alpine plants that need relatively little soil or water. Western rock gardens are often divided into alpine gardens, scree gardens on looser, smaller stones, and other rock gardens.
 
Google Groups: alt.vampyres
Vamp Goddesses and FOOD FIGHT!
Steven Van Tilburg
Feb 11, 1995, 4:27:09 PM
(...)
VT - : I once had a rock garden
: but they all died.
   
Google Groups: alt.alien.research
REAL PROPHET?
Palm
Jan 16, 1998, 3:00:00 AM
(...)
.. I used to have a rock garden—they all died.
___ Blue Wave/QWK v2.12
 
Google Groups: alt.tv.star-trek.voyager
To All Star Trek Voyager Fans:
Bozo the Proctologist
Dec 21, 1998, 3:00:00 AM
(...)
I used to have a rock garden—they all died.
     
Google Groups: uk.telecom.mobile
t610 help
Tony Sutton
Oct 29, 2003, 3:15:25 PM
(...)
I used to have a rock garden—they all died.
 
Twitter
Terry Fernihough
@trfernihough
Replying to @cdtellier
I had a rock garden. Unfortunately, they all died.
6:56 AM · May 28, 2019·Twitter for Android
 
Twitter
Blake live from down under🔴
@bj_flemming
Replying to @vodkanopants
I had a rock garden once, they all died
3:25 AM · Mar 17, 2021·Twitter for Android
 
Creators Syndicate
Announcing ‘Greener View Gardening’ Book and Videos
By Jeff Rugg
June 1, 2022
In two months, I will have been writing a weekly newspaper column for 32 years. During that time, I have written about books created by many garden writers. Now it is my turn. I have written a book on gardening.
 
“Greener View Gardening” was written to help homeowners understand and care for their lawn and garden. Does this old joke sound like you? “I am such a bad gardener. I once planted a rock garden, but they all died.”