The Astros had hoped to pick up Garland to replace Andy Pettitte, who signed a free agent contract with the New York Yankees, but that deal fell apart.
Houston ended up with Jennings and Asencio, sending outfielder Willy Tavares and pitchers Taylor Buchholz and Jason Hirsh to Colorado.
Jennings was the key for Houston. The Dallas native was 9-13 with a 3.78 ERA for the Rockies last season and is eligible to become a free agent after next year. He is the Rockies' all-time leader in wins with 58 and in shutouts with three when pitching at hitter-friendly Coors Field.
Trachsel joins Orioles
Jennings is expected to be the number two starter in Houston behind Roy Oswalt. The Astros are still waiting to see if seven-times Cy Young Award winner Roger Clemens will return for another season.
Asencio was 1-0 with a 4.70 ERA in three games with Colorado last season, but spent most of the year in Triple-A.
Tavares hit .278 with one home run and 30 RBI in a season that included his 30-game hitting streak.
Buchholz was 6-10 with a 5.89 ERA with the Astros and had arm problems last season. Hirsh is a highly regarded 24-year-old prospect who went 3-4 with a 6.04 ERA in his nine starts.
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