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3/7/2014 2:48 P.M. ET

Jackson: Game will tell if young stars are ready

MESA, Ariz. -- Edwin Jackson was 20 years old when he made his Major League debut in September 2003. The pitcher has seen the young talent in the Cubs camp, including Kris Bryant, who hit his second spring homer on Friday, and is wondering the same question most fans are asking:

When is the right time to promote them to the big leagues?

"There's no specific age or time," Jackson said. "The player will let you know when he's ready or when he's not. Nowadays, I think you've got guys all over the league on all different teams coming up 19, 20 [years old] and having success.

"I don't think there's one particular formula that works," he said. "It's different for every person. One thing for sure, you find out, the game will tell if they're ready or not."

Bryant's been on the fast track since he was selected second overall in last year's First-Year Player Draft. He played for short-season Boise, then was bumped up to Class A Advanced Daytona and finished in the Arizona Fall League. Now, he's in the big league camp. Top prospect Javier Baez also has two home runs this spring. Bryant is 22; Baez 21.

Jackson had appeared in 58 games before he made his big league debut. He did pitch again in the Minor Leagues from 2004-06. Did he get the call too soon?

"Who knows? I think [there's different opinions]," Jackson said. "You could say I was, you could say I wasn't. It made me a stronger person because I learned how to deal with adversity at a younger age. I think it made me stronger.

"It's tough to go out and learn how to deal with failure," he said. "I guess I had the luxury of when I did learn how to deal with failure is that it was at the big league level. I went through the Minor Leagues without struggling, so most of my struggles came in front of a television [audience]. It definitely makes you a stronger person. It molded me into the person I am today and to feel like whatever happens, I can make it through it."

On Friday, Jackson said he threw only fastballs against the Indians because that's all he wanted to work on. If other pitchers are doing the same and using Cactus League games to experiment, is Spring Training a fair gauge of a player's talent?

"They still have to hit it whether you're working on your fastball or not," Jackson said. "These guys are young, they're agile, they're flexible, they're strong and they're getting the bat through the zone. It's hard to say just because he's hitting or not hitting now that he won't be hitting or will be hitting down the road.

"Baseball's a crazy game, and you just never know," he said. "You see people have poor Spring Trainings and then once the season starts, they catch on fire. ... It's just a crazy game we play, and you never know about one particular person."

Castro feeling better, intent on playing every day

MESA, Ariz. -- Cubs shortstop Starlin Castro, sidelined since Sunday with a mild right hamstring strain, hopes to begin baseball activities early next week, and has the same goal as years past of playing all 162 games.

Castro, injured when he tried to steal second base in a game, is taking advantage of the Cubs' new hydrotherapy pool and doing exercises there twice a day. It's helped speed up his rehab.

"I don't feel any hurt or tightness," Castro said Friday. "It feels much better. I don't want to rush myself. I want to be 100 percent."

His goal every season is to play every game, which he did in 2012. Last year, Castro had a strained left hamstring in Spring Training, recovered and played 161 games.

"That's my goal every year," Castro said about playing all 162 games. "That's why this [injury] is better to happen now, hurt now, and not during the season. I'm going to be 100 percent for the season."

He is coming off his worst offensive season, when he batted .245, and is enjoying his work with new hitting coach Bill Mueller.

"I feel a little frustrated becuase I felt really locked in when I was hurt," Castro said. "I felt so good at home plate. It was only one week here, the games started, and I already felt good at home plate. That [feeling of being] locked in, it won't go away. It'll stay there. I'm going to stay locked in."

He's able to do some upper-body exercises while he nurses his sore hamstring. After devoting so much time in the offseason to preparing for this year, Castro is frustrated at the injury.

"I don't like being hurt," he said. "It's not good. I prefer to go on the field, run, get ground balls. I don't want to be in the pool. I want baseball activity."

Barney sees value in getting comfortable at shortstop

MESA, Ariz. -- Darwin Barney wasn't sure how it would feel being back at shortstop, and the Indians didn't waste any time testing him on Thursday.

Cleveland leadoff man Michael Bourn hit a slow roller to Barney to start the game, and he cleanly fielded it and threw the runner out. And that was the last ball hit to him.

A Gold Glove second baseman in 2012, Barney started at short while the Cubs wait for Starlin Castro to heal from a mild hamstring strain.

"There was a time when going back to shortstop felt more comfortable than playing second base, and that was probably the first two years when I moved," said Barney, who was a shortstop before switching to second full-time in 2011. "Over time, that feeling goes away. Now, I felt like I had to really focus on certain things.

"After a few innings, I felt really comfortable and you find out how much you miss that position," he said. "It's part of the game. I found out I'm a really good second baseman, and I'm happy there, too."

What's next? Cubs manager Rick Renteria says he'll continue to rotate the infielders. Barney expects he'll be back at second base, but Renteria is getting to know the roster and what the players can and can't do.

"As we continue to go through our workouts, he'll remember," Renteria said of Barney at short. "I think a lot of his movements are natural. He was over there a long time."

On Friday, Barney was the designated hitter in one of the Cubs' split-squad games, which was a chance for more at-bats. He wouldn't mind more playing time at short.

"I think I have value [at shortstop]," he said. "I'm pretty good over there, and I like it over there, too."

Extra bases

• In 2007, Neil Ramirez boasted the best curveball among all Minor League pitchers. At least, that was the grade he got from Baseball America. Ramirez laughed when reminded of that.

"I used to throw it a lot more than I do now," the pitcher said Friday. "I gravitated more to the changeup now. The curveball is still there."

Ramirez, whom the Cubs acquired from the Rangers as the player to be named in the Matt Garza deal last July, has developed a few other pitches to go with his curve. He learned how to throw the curve while in high school from former Giants pitcher Gary Lavelle, now 65.

"He taught me the grip and taught me to throw it a certain way," Ramirez said. "I don't try to manipulate it too much. It just kind of works."

Kyuji Fujikawa, rehabbing from Tommy John surgery on his right elbow last June, threw off the mound for the fourth time this spring and continues to make progress. The Cubs have not set a timetable for his return.

• The University of Tennessee baseball team was a guest of the Cubs at the morning workout and got a tour of the facility. The Volunteers, 12-0 and ranked 19th in the nation, are in town to play Arizona State this weekend.

• Hall of Famer Billy Williams, 75, was at Cubs Park on Friday. When he played with the Cubs in the 1960s, they trained at Rendezvous Park in Mesa and used a high school field.

Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.