“Rain makes grain”

“Rain makes grain” is mostly a financial saying, popular at markets that trade in grain such as the Chicago Board of Trade. “The old farm saying ‘rain makes grain’ was working yesterday” was cited in print in 1976.
 
“Maxims connected to agriculture can be heard on the exchange floors; for example, ‘Rain makes grain’ and ‘Plant in dust, and your bins will bust’” was cited in a 1988 book on Wall Street slang.
 
 
6 February 1976, New York (NY) Times, “Potato Futures Advance Sharply” by Elizabeth M. Fowler, pg. 50:
The old farm saying “rain makes grain” was working yesterday.
 
17 August 1984, Pharos-Tribune (Logansport, IN), “Markets: Grain,” pg. 2, col. 3:
Rain makes grain was the common cry across the floor.
 
Prices fell in response to overnight rain in parts of the Midwest and forecasts for additional rain today.
 
5 June 1987, Aberdeen (SD) American News, “Optimism arises in grain markets” by Hugh McDonald, Farm Forum, pg. 1, col. 1:
The market remembered the old adage “rain makes grain” and prices lost part of their earlier gains.
 
Google Books
High Steppers, Fallen Angels, and Lollipops:
Wall Street Slang
By Kathleen Odean
New York, NY: Dodd, Mead
1988
Pg. 152:
Maxims connected to agriculture can be heard on the exchange floors; for example, “Rain makes grain” and “Plant in dust, and your bins will bust.”
 
Google Books
The Complete Idiot’s Guide to Options and Futures, 2nd Edition
By Scott Barrie
New York, NY: Alpha Books
2006
Pg. 145:
Generally, you should remember the old battle cry of grain traders on the Chicago Board of Trade: Rain makes grain.
 
Google Books
Commodity Market Fundamentals
By Carley Garner
[Upper Saddle River, NJ: FTPress Delivers
2011
Pg. ?:
You have likely heard the mantra, “rain makes grain.” It is said that during the grain growing months, the bias on the floor of the Chicago Board of Trade is negative if it is raining in downtown Chicago. This is because the windy city is located in the heart of the grain belt, and if it is raining on Wacker Drive, it must be getting to the nearby corn fields, and this promoted higher production yields.
 
Inside Futures
Have the Grains Traded this Weather Yet?
Thursday, April 18, 2013
by Ted Seifried of Zaner
(...)
The old adage rain makes grain certainly holds true when its in the ground but until then markets should be concerned, and be adding incentive to get planting done.