Figuring out what will and won’t grow

How Duke Gardens is managing a changing climate

By Corbie Hill

Just past the staff-only gate grow the plants that shouldn’t be.

Here is a variegated agave and a mangave that somehow survived a North Carolina February. Here is a saw palmetto, native to coastal Georgia, which should not be thriving, and here is a sago palm, which should be dead. That dry yellow stubble is ginger and that shrub is a coral bean—both punished by the climate, but not fatally—and this cycad, a prehistoric plant that looks the part, really should be inside a greenhouse. Even the fig vine blanketing the wall behind the gravel bed of the Sarah P. Duke Gardens’ experimental plot would not have thrived in earlier, cooler eras.

“This whole bed is an experiment of, Can we push these things to grow?” says Duke Gardens director of horticulture Bobby Mottern. “We’re willing to roll the dice and sacrifice and see what happens.”

To a horticulturalist, it is of course exciting to grow plants native to Mexico or coastal California in historically temperate North Carolina. Then again, these experiments are only possible in the era of climate change. For native plants accustomed to colder winters and cooler nights, a warming world can interfere with metabolism and bloom cycles or exacerbate the threat of pests and disease. Sure, spring hits differently every year, and sure, mild spells are nothing new, but today’s mild spells are milder and last longer, Mottern says. The climate is changing, and so is what will grow—and won’t.

“Plants need a chance to catch their breath, so to speak,” he says. If it’s too warm, and especially at night, they can’t rest and recover from the day, he continues. This is when North Carolina natives like the white pine suffer.

An early spring throws plants’ patterns into chaos, causing premature blooms. Redbuds, which typically bloom in late March and early April, revealed their magenta hues in early March. Duke Gardens’ charismatic cherries allée very nearly bloomed in February. “It’s becoming common that a lot of plants are blooming ten days to two weeks early, almost on an annual basis,” says Mottern.

We’re willing to roll the dice and sacrifice and see what happens.

This is problematic for a botanic garden that draws out-of-state visitors, many of whom plan their trips around cherry blossoms or the Terrace Gardens’ tulips. Even more troubling are potential repercussions in ecosystems themselves. Many birds feed on insects, and many insects feed on nectar—this is a given. Mottern is concerned about what happens when plants bloom before the insects that feed on them emerge.

So how does a botanic garden, a place with conservation baked into its DNA, pivot in a warming world? To answer, Mottern hops in a golf cart—Duke Gardens doesn’t burn petroleum if it can help it—and gives an impromptu sustainability tour. “Doing everything that you possibly can to limit your carbon footprint is really what everybody needs to do,” he says.

First stop, a mountain of sticks, branches, and pallets from Duke’s gardens and grounds. Every year or so, DUKE GARDENS grinds 3,000 cubic yards of landscaping debris into 600 cubic yards of mulch and compost. Only organic fertilizer is used, and pesticide is verboten. If mites attack a plant, the plant goes. The only exception to the pesticide ban is for the exotic invasive fire ant.

Mottern points out examples of reuse. These benches were once sidewalk curbs. And this is castoff stone used in Duke Gardens’ drainage system, which guides water through a seventy-two-foot difference in elevation at such a pace that minimizes erosion but waters plants along the way. “It’s not just here to be pretty,” Mottern says. “There’s a purpose to it.”

The cart crunches along the path, and soon it’s in the open, under clear skies and warm sun. It’s early March, and parents play with babies and young children in the open field below Flowers Drive. Teenagers sit flirtatiously close on what they somehow think are secluded benches. A young couple salsa dances in the grass with jubilant abandon. It’s a beautiful day—the kind Duke Gardens is famous for.

It’s just here too early.