Garner, 22, has scored nine goals for Forest in 51 appearances since a £1.14million move from Carlisle in 2008.
He fell out of favour at the City Ground and has spent the first-half of this season at the League One side Huddersfield Town, where he failed to score.
"He's played on the right wing, the left wing and considers himself as a striker," said the Iron manager Ian Baraclough.
"That's where he prefers to play but he's someone who is adept at playing in one or two different roles, so that's useful. He's a forward player and we will certainly utilise his abilities.