Every year without fail, dozens of tulips pop up in the Public Garden and throughout Boston, signaling spring and the promise of warm weather — but they don’t just grow on their own.

The man behind the magic is the city’s superintendent of horticulture, Tony Hennessy. Every year, he leads a team of 20 people to grow 30,000 plants in the city’s 16 greenhouses. They work diligently to make sure the plants are watered, healthy, and ready to grace the city’s sidewalks and parks.

In the fall, the city starts planning for the spring — deciding which plants to feature and how many seeds and bulbs it will need to order.

“This year, we’re featuring a plant called the dutchman’s pipe,’’ Hennessy said. “It’s a large plant that has a white and yellow large flower that hangs upside down.’’

In addition to the plants the city grows on its own, about 15,000 come from elsewhere.

“There’s some exotic stuff, like tropicals and what not, and palm trees,’’ Hennessy said.

Hennessy’s pride and joy is the Public Garden, which was the first of its kind in the United States. He said he takes that designation seriously and works hard to keep it enjoyable for all.

But having such a haphazard winter such as this year’s can make planning harder, and can be especially “confusing’’ for perennials, Hennessy said. “It’s definitely delaying some planting,’’ he said. “We really can’t work the soil until it’s unfrozen. It kind of stinks.’’