PHOENIX — In a move they hope will add stability to a young and unproven rotation, the Rockies signed veteran right-hander Jon Garland to a major-league contract Sunday.

He becomes the Rockies’ fifth starter, meaning left-hander Drew Pomeranz probably will be sent to Triple-A Colorado Springs. There is a chance Pomeranz could pitch as a long reliever out of the Rockies’ bullpen.

Garland, 33, signed a one- year contract worth $500,000, with incentives. He is a sinkerball pitcher with a career 1.31 groundball-to-flyball rate.

“He profiles for us and the things we are trying to do,” said manager Walt Weiss. “He’s a veteran and he has some stripes on his shoulder from his experience in the game. There is some youth to our club, so he helps us from a stability standpoint. We’ll see how it goes.”

There are no guarantees that Garland will be an upgrade. He hasn’t pitched in the majors since 2011, when he went 1-5 with a 4.33 ERA for the Dodgers as he battled shoulder pain. After missing the entire 2012 season following shoulder surgery, he signed a minor-league deal with Seattle in February. He pitched well, going 1-0 with a 2.25 ERA in four Cactus League starts.

But when it became clear he wasn’t going to make the Mariners’ rotation, he asked for his release Saturday. Once that was granted and he became a free agent, Colorado moved in quickly.

The big question now becomes what the club does with the talented but still unpolished Pomeranz. Despite an uneven spring, (5.50 ERA in five games, four starts) he appeared to have earned a spot in the rotation.

“We haven’t discussed Pomeranz being in the middle (relief) role,” Weiss said. “If he didn’t pitch in our rotation, he would most likely be (sent to Triple-A). The Garland thing just happened, so we haven’t talked about the Pomeranz situation.”

Garland has a career record of 132-119 with a 4.32 ERA while pitching for the White Sox, Angels, Diamondbacks, Dodgers and Padres. He was an all-star for the White Sox in 2005 when he went 18-10 and helped lead them to the World Series title.

Other roster moves. Colorado cleared space on the 40-man roster by returning left-hander Danny Rosenbaum to the Nationals. The Rockies selected Rosenbaum in the Rule 5 draft in December.

In the first wave of late-spring moves, the Rockies optioned right-hander Tyler Chatwood and lefties Josh Outman and Christian Friedrich to the minors. All three likely will begin the season as starters for Triple-A Colorado Springs.

The other players sent down: right-handed reliever Rob Scahill (optioned), infielder Charlie Culberson (optioned), first baseman Ben Paulsen (assigned), catcher Gustavo Molina (assigned) and outfielders Charlie Blackmon (optioned) and Corey Dickerson (assigned). Those players who were optioned are still on the Rockies’ 40-man roster.

The Rockies now have 36 players on their big-league spring training roster, including nine players not on the 40-man roster.

De La Rosa update. Left-hander Jorge De La Rosa, scratched from his scheduled start Saturday because he felt forearm tight- ness during the week, threw 36 pitches in two innings during a Rockies intrasquad game Sunday. De La Rosa’s arm felt good, according to the club.

Patrick Saunders: 303-954-1428, psaunders@denverpost.com or twitter.com/psaundersdp