"As soon as I knew that [we were writing our own vows], I started trying to write a song because that's the opposite of what she would have expected me to do," he said. "I'm to the point where I just don't write that many songs anymore. It's just like pulling teeth for me and something she's always on my case about it."
"And so I started writing this song and I can only get so far with it, 'cause I didn't want it to just be something for that moment," Shelton added. "I wanted it to be something that was bigger and I saw I needed help. And so I called Craig Wiseman. I said, 'Craig, you got to help me with this thing. Like, I'm not joking around here.' You know?"
Wiseman ended up helping Shelton write a track for Stefani, 51, that he "wouldn't be embarrassed about." He explained that he wanted the song to be broader but "also specific to Gwen."
Kevin Mazur/BBMA2017/Getty Blake Shelton and Gwen Stefani
"She didn't know I was going to do that," he said. "And so I surprised her with the song and we actually just recorded the song here in Nashville yesterday. I don't know what, or when we're going to do something with it, but it's something that I wanted to have a recording of."
Shelton said he's actually "really proud" of the song, as he is of being married to Stefani.
"You're not keeping it private when you get married to somebody," he said. "You're announcing to the world, 'Hey, this is my wife, just so everybody knows.' That's why we wear these rings. This is where we're together now. And I feel that way about the song. I want people to hear and know."
"I'm proud to be married to Gwen and so proud of that song," he added.
Shelton also revealed that he and Stefani have yet to go on a honeymoon together and instead chose some "quiet time" in Oklahoma.
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"We still are probably going to [go on a honeymoon]. We did have some time after the wedding, just she and I, but you know, we just wanted something calm for a minute and not to run off and then go do something else," he said.
"Since she's spending more time in Oklahoma. She's realizing that the agriculture part of Oklahoma and the things that you can do, and her passion — outside of music — is flowers," he added. "This past spring, when we had time, we went and planted a few acres of just zinnias... man, we've had all this rain this year and wildflowers — acres of those things. She's in absolute heaven with that. And so she wouldn't have wanted to leave anyway, because she can just literally walk out there and stand in acres of those things."
Terry Wyatt/Getty Blake Shelton and Gwen Stefani
Earlier this week, Shelton and Stefani had a sweet moment on stage when she joined him on stage and he called her "Gwen Stefani Shelton."
Stefani and Shelton said "I do" in a backyard chapel on his ranch on July 3, cheered on by an intimate group of 40 of their close friends and family members, including Stefani's sons (with ex Gavin Rossdale), Kingston, 15, Zuma, 12, and Apollo, 7, and longtime pal Carson Daly, who officiated.
"It was everything they wanted: family, friends, dancing, the beauty and familiarity of the Oklahoma surroundings and lots of love and laughter," a music industry source told PEOPLE at the time. "It couldn't have been better."