Gardner followed the example of Ridgewell in switching from Villa to their local rivals because of his desire for regular first-team football.
It has paid dividends for both players and Gardner is now City's leading scorer after netting his ninth goal of the season in Saturday's 2-0 home success over Sunderland.
Defender Ridgewell told Press Association Sport: "Craig is benefiting from playing regular football. It was difficult for him coming in and out of the side at Villa.
"It was like me. I wanted to come here after playing so much at Villa for a spell and then going onto the bench. I wanted to come here and play and Craig has done the same and you reap the rewards from playing football week in and week out.
"The goals he has scored have been vital and it was a big one to take us away from Sunderland at 2-0 and give us breathing space."
Ridgewell added: "It is a hell of a boost to have a midfielder who can score goals. He has got some vital ones this season. I was right behind Craig's shot for the second goal against Sunderland and it dipped and swerved.
"He has got a great strike with either foot and has produced some great strikes this season."
Source: PA
Source: PA