SAN FRANCISCO — On a sunny Saturday in March, more than 40,000 people filed through San Francisco’s Union Square to get a glimpse of the 80,000 yellow, orange, and red tulips on display.

The flower garden opened at 1 p.m., but that didn’t stop people from getting in line hours earlier, shovels and bags in hand. The rule was that they could dig up eight tulips to keep until the flowers ran out.