"He shook my hand, said congratulations," Hirsh told MLB Radio on Wednesday. "I was in shock."
Hirsh said he had no idea he was going to be called up. He will get the start on Saturday against the visiting San Diego Padres.
Hirsh had already played with the Astros during spring training.
"He didn't impress me in spring training," Houston Astros Manager Phil Garner told MLB.com. "It proves that you can't do yourself any harm as long as you work hard and put forth a good effort. I think his back bothered him in spring and he never was right. We didn't really see the true pitcher that he's been now.
"It will be interesting to see how he throws. He's been pitching very, very well. He impressed everybody down there and everybody in our system. We'll give him a shot up here."
Hirsh leaves behind a 13-2 record with the Express, good enough for tops on his team and the Pacific Coast League.
Fernando Valenzuela Jr. (St. Francis High, 2000 and Glendale Community College, 2002), first baseman, Kannapolis Intimidators — Things seem to be improving for the 23-year-old Valenzuela since becoming a member of the Intimidators on June 2. Through Tuesday, Valenzuela was batting .273 (57 for 209) with eight home runs and 31 runs batted. He's registered 12 doubles, two triples and scored 29 runs in 58 contests for Kannapolis, which is a class-A affiliate of the Chicago White Sox in the South Atlantic League.
Valenzuela, who helped Glendale College win two Western State Conference Southern Division championships, had a single Tuesday for the Intimidators in an 8-4 loss to the visiting Delmarva Shorebirds.
He hit a solo home run in the fifth inning to help pace Kannapolis (17-36) to a 7-5 victory against Delmarva on Monday. Kannapolis entered Wednesday's game against Delmarva in last place in the league's Southern Division after capturing the division championship last season.