The 36-year-old actor tied the knot with the "Twilight" actress last month.
Gushing over Reed, Somerhalder said world is a better place because of her.
"Happy birthday to the most incredible woman I've ever known... HAPPY BIRTHDAY @NikkiReed_I_Am The world is better because you are in it!!!!!" he tweeted.
"I meant the most incredible human I've ever known...," the actor posted.