Tharmes, 20, rose through the youth team ranks at Wrexham before securing a professional deal in 2018.
He is the first of three expected new signings from Curtis Woodhouse.
"I am delighted to get Doug over with us from Wrexham; he is a real promising young player," said the manager.
"After getting a glowing reference from Bryan Hughes, it was a no-brainer to help him with his development.
"I know they have really high hopes for him over there. He just needs game time to help him develop and go on and have a really good career. It's an initial month’s loan, but we will then see how it goes from there."
The deal will be subject to all relevant paperwork being completed, including international clearance due to the signing requiring ratification by both the Welsh and English Football Associations.
The club have also announced that Billy Chadwick has returned to Hull City following his loan period.
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