I don't remember much about the story in general, but here's the details I can recall.
It's a short story, intended for a 5th or 6th grade reading level, and I found it in the early 2000s in a collection of stories, the rest being lost to memory. In the story, somehow a kid finds out his neighbor has a time machine in his garage, or his neighbor might have told him about it. Either way, his neighbor proves his time machine by procuring a fully blooming rose in the middle of December.
I can't remember the end. It might have been published before 2000, maybe after.