My tulip tree is 26 years old here in zone 4, Minnesota. The coldest it has seen is minus 36°F (-38°C). It has been blooming now for eight years. The trees are rare here, too, although the Minnesota Arboretum ten miles away has a couple. I do get seedlings that come up in the lawn and lightly mulched areas. Of course, if you spray or treat your lawn for weeds, you would be killing the tulip tree seedlings, too. They don't look like tulip trees when they are small, and if you mow your lawn regularly as a normal person would, it's likely you would never see them.
