The catcher, Houston's first pick -- No. 10 overall -- in the 2008 First-Year Player Draft, agreed to terms with the Astros and will be headed to Class A Tri-City on Monday.
"It's been a whirlwind," the former Stanford backstop said in his first trip to Houston. "It's been a blast, and I've loved every minute of it. Now I'm looking forward to just going out and playing baseball."
Castro, who was recommended and signed by Astros area scout Joe Graham, was given some recuperation time before contract negotiations began. Stanford was in the College World Series, and Houston could not contact him until after the Cardinal's run ended June 21.
Astros director of amateur scouting Bobby Heck said Castro was the most instrumental figure in speeding up negotiations, and he was pleased with the pace of the process.
"Obviously you want to have him right after he's done playing," Heck said. "But if you look at the top 10 picks, this is the second guy to sign and probably the guy who's had the smallest window to sign in. As far as the pace of this, yeah, it was outstanding. He's still going to get the bulk of the summer to go out to play."
Castro, a 20-year-old, 6-foot-3, 210-pound college junior from Castro Valley, Calif., helped Stanford to a 41-24-2 record with a .376 average, 14 home runs and 73 RBIs in 67 games. He was an All-Pac-10 player this season, ranking in the top 10 in multiple Pac-10 categories.
He also played in the Cape Cod Summer League last summer, batting .341 (second best in the league) with 24 RBIs, earning an All-League and CCBL All-Star selection.
Castro's parents, Tom and Lori Castro, joined their son at the Saturday afternoon press conference and said they were overwhelmed with excitement.
"It brings tears to my eyes," said Lori Castro, who wore an Astros pendant around her neck. "We're so proud, I can't even tell you. It's a dream for all of us for him, and it's something he's looked forward to since he was seven years old."
Tom Castro said they let their son make the ultimate decision regarding contract terms and other fine points, although they did give him guidance along the way.
Graham said he was impressed by Castro's leadership ability and his presence behind the plate as soon as he started scouting him in February. He said he expects Castro to be a face in the Astros organization for many years to come.
"He's a complete player," Heck said. "He's an athletic catcher who's offensive. He has defensive abilities and skills but is also very intelligent, because there is a mental demand on that position. With the Stanford pedigree, he qualifies there."
As for what he is going to do now, Castro will have an odd way of celebrating his new job.
"Just getting my work in is what I feel I need to do," he said. "I'm going up to play, and I think that's kind of a celebration in itself, to get started."
Krysten Oliphant is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.