Director of amateur scouting Bobby Heck and his staff were to visit Castro at his home this weekend for negotiations, which are ongoing.
The Astros couldn't begin negotiations until after Castro and Stanford were eliminated from the College World Series in Omaha, Neb., which happened on Saturday.
"We're still optimistic that we'll get this figured out, it just takes time," Wade said. "There is still more legwork to get done."
Houston is also still trying to sign first baseman Chase Davidson, its third-round pick out of Milton (Ga.) High School, along with Brad Dydalewicz, a left-handed pitcher who was taken No. 272 overall out of Lake Travis High School.
Ross Seaton, the local righty from Second Baptist, is trying to come to terms with the Astros as well.
The Astros have signed a total of 26 players so far, including left-handers Luis Cruz (Academia Santa Monica, San Juan, P.R.) and Jarred Holloway from St. Petersburg, Fla. Thirteen pitchers and 14 position players have been signed so far.
"We're making progress on all fronts," Wade said. "It just takes time. There's a lot of undone deals right now out there with respect to the Draft."
Krysten Oliphant is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.