Many people never stumble upon the lush world of the City Park greenhouses, just west of the Denver Zoo. Yet these nondescript buildings at 2500 E. 23rd Ave. supply Denver’s parks with dazzling arrays of flowers, help grow fresh produce for needy families and keep zoo gorillas happy with a steady supply of hibiscus flowers — one of their favorite snacks.

This spring, after two years of grappling with manpower shortages and cost issues spawned by the pandemic, the 36,000-square-foot nursery is back in business. In late May, flats of fiery-colored Indian paintbrush, pastel petunias, cascading blue lobelia and many other plants began departing their warm, steamy home, bound for Denver’s 250 city parks.

According to Denver’s Horticulture and Open Space Manager Julie Lehman, the parks’ ornamental beds will be planted at 100 percent this year — a joyous change from all the bare soil on view during 2020 and 2021. Many parks, including Washington, City and Alamo Placita, will offer especially dramatic floral displays.

Lehman and her staff preside over a humid plant kingdom, where a seemingly endless expanse of grow benches support the 250,000 seedlings that emerge every spring. The hothouses nurture not just flowers, but enough vegetable starts to generate 13,000 pounds of tomatoes, peppers, cabbages, kale and eggplant.

The vegetables are tended by local nonprofits and used to help feed low-income families. Three of the hothouses are operated by zoo staff, who grow hibiscus, bananas and ginger for the animals to snack on, along with plants that serve as landscaping and browse for munching giraffes.

Over the years, as Coloradans have grown more environmentally conscious, the greenhouses have followed suit. Lehman says she stopped using pesticides several years ago, and now relies on beneficial insects to keep the pests at bay. She also noted a shift towards native flowers and other plants that nourish the soil and require less water.

Vastly outnumbered by their leafy charges, Lehman and her staff of four rely on 20 freelance master gardeners and 40 horticulturalists, who pitch in to get the parks planted every year.

Lehman reviews all designs personally, taking many factors into consideration. Agastache and chocolate daisies, for instance, thrive in the sandy soils of eastern Denver, whereas asters and showy pink echinacea, also known as coneflower, prefer the clay soils of western neighborhoods like Capitol Hill and Washington Park.

Lehman, who grew up on a ranch in Nebraska, still cherishes a fondness for prairie flowers, including purple prairie clover, agastache, Indian paintbrush and penstemons. Many of these are also native to Colorado and have a nice habit of giving more than they take from the soil. She is also partial to those chocolate daisies, a Southwestern native that enjoys hot, dry conditions. Look for them on sunny traffic medians in eastern Denver and if you get the chance, inhale. They aren’t called chocolate daisies for nothing.

This year, it’s been a challenging spring, with unseasonable heat forcing many seedlings to jump and flower too early, according to Lehman, who has been on the job for a decade. She said Denver has a short growing season because of its wildly variable weather, sudden freezes and limited water supply — all exacerbated by climate change.

Despite the hurdles, Lehman observed with pride that Denver has a long history of horticulture. The City Greenhouse began as a Victorian-style palm house, built in 1892. In the 1940s, the city built its first modern greenhouses, giving them major updates in 2005 and 2010. The original 19th century conservatory building now houses the aviary at the Denver Zoo. And fittingly, the aviary’s feathered residents are now benefitting from the modern nursery next door.