“Its not record science”—that is, it’s not complicated—is an expression that has been popular since at least the 1980s. “It’s not rocket salad” is a joke based on the expression. The plant Eruca sativa is also known as “rocket salad.”
   
“I thought growing my own lettuce would be difficult but it was quite easy in the end.  It’s not rocket science” was posted on Twitter by jryskowski on October 1, 2010. “Gardening isn’t rocket science, unless you’re growing lettuce” was posted on Twitter on September 10, 2011. “Trying to grow ‘Eruca Sativa’ lettuce next year… It can’t be rocket science, surely?” was posted on Twitter on October 8, 2012.
 
     
Wikipedia: Eruca sativa
Eruca sativa (syn. E. vesicaria subsp. sativa (Miller) Thell., Brassica eruca L.) is an edible annual plant, commonly known as rocket salad or arugula; other names include rucola, rucoli, rugula, colewort, and roquette.
 
Twitter
jryskowski
@jryskowski
I thought growing my own lettuce would be difficult but it was quite easy in the end.  It’s not rocket science.
3:59 PM - 1 Oct 2010
 
Twitter
Wolfgang Ramadeus
@wolfeeboy999
I thought growing my own lettuce would be difficult but it was quite easy in the end.
It’s not rocket science.
1:58 PM - 27 Feb 2011
   
Twitter 
Sebas
@OhLookBirdies
Gardening isn’t rocket science, unless you’re growing lettuce.
1:27 PM - 10 Sep 2011
   
Twitter
Mark Summers
@markysumm
Can growing your own lettuce be considered rocket science?
10:56 AM - 12 Nov 2011
 
Twitter
Kate Robbins
@KateRobbins
Trying to grow ‘Eruca Sativa’ lettuce next year… It can’t be rocket science, surely?
11:27 AM - 8 Oct 2012
         
Twitter
GlasgowScienceCentre
@gsc1
I thought growing my own lettuce would be difficult but it was quite easy in the end. It’s not rocket science. #badsciencejoke
11:22 AM - 8 Feb 2013
 
Twitter 
Stephen Mulhern
@StephenMulhern
I thought growing my own lettuce would be difficult but it was quite easy in the end.  It’s not rocket science.
2:26 PM - 23 Feb 2013
 
Twitter
Gizzy
@gizm0j0e
I thought it would be hard to grow your own lettuce, but its actually quite easy.
Its not rocket science.
12:43 PM - 25 Oct 2013
   
Twitter
Statto
@HeadlongCabbie
How hard can it be to grow a particular type of lettuce?
It’s not rocket science
1:50 PM - 3 Sep 2015
 
Twitter
Andy Purchase
@1AndyPurchase
@ShitJokes
Pupil: How do you grow lettuce in a laboratory?
Teacher: Well it’s not rocket science.
2:52 PM - 4 Nov 2017
 
Twitter
Thucky 👤
@Thuckster__
I always thought growing lettuce would be hard. Turns out it’s not rocket science.
9:35 AM - 12 May 2018
 
Twitter
Ron
@upminster13
I thought growing my own lettuce would be difficult but it was quite easy in the end.
It’s not rocket science.
5:11 PM - 10 Jul 2018