Montag turned the big 2-2 Monday with a picnic with beau Spencer Pratt.
"I got some amazing gifts and a cake that said, 'Happy Birthday, Princess Heidi!'" she said Tuesday on Ryan Seacrest's KIIS-FM radio show.
And although Pratt didn't surprise her with a ring, he told Seacrest their engagement "is definitely imminent."
As for that rock, Pratt (who was previously engaged to Montag before they briefly split) said, "she's dreaming big."
Pratt added that Montag has also been nagging him about starting a family.
"Heidi talks about lots of kids all the time," he said. "She wakes up with these great dreams about five kids."
Montag then interrupted, "I want, like, four. Maybe I'll adopt 10. I want to have my own orphanage like Mother Teresa."
For now, Pratt said, "I am fighting her everyday - [she wants] kittens and puppies."
Has Montag's latest milestone given her a change of heart when it comes to foe Lauren Conrad? (On Monday's episode of The Hills, both admitted they miss each other.)
"It's hard to say, and I don't talk to her about it," Montag said. "Obviously, a part of her misses me, and we were close. It's natural to miss each other."
But she doesn't want the bickering to carry on.
"I'm 22 now, so I'm really grown up," she went on. "Life is really short, and I don't need negative energy. There are children who are sick in the worst and, like, important matters, and it's such a waste of time to be fighting and angry."