Climate change is coming for New England's cranberries

When the Davenport family bought the 12-acre cranberry bog in a small Cape Cod town five years ago, they knew it wouldn’t be easy to care for, but they were ready for it all: digging through poison ivy vines tangled in with the cranberry. Avoiding the spiders skittering up the rakes and booms used to collect the deep red fruits from flooded bogs. Sleeping in the truck next to the bog on cold nights, ready to spring into action with sprinklers to protect the fruit from freezing.

But every autumn, the triumph of harvest makes it all worth it, says Tabatha Eldridge, the bog owner's wife. The russet leaves on the bog, the chilly tannic water, her husband and son wading across the spongy surface and gently ushering the bobbing fruits toward the waiting truck: That’s what they work for.

The fruit they love is the result of millions of years of evolution, thousands of years of human consumption, 200 years of intentional cultivation, and their own years of dedication. But how the viney plants will fare in the future is far from certain. In New England as elsewhere, climate change is shifting many of the conditions under which the plants thrive, from warming winters to changing summers. The changes are making them harder to grow and putting a question mark next to the iconic, beloved crop’s future.

Growers that love their crop and the scientists that help them are working to figure out solutions, and the situation isn’t yet dire. But for growers like Eldridge, so far, “we don’t really have a Plan B,” says Eldridge.

The fruit adapted to the harsh New England climate

Cranberries have very specific needs.

They’re one of only three fruits commonly cultivated that are native to North America, along with Concord grapes and the cranberry’s close cousin, the blueberry. The bracingly tart “sour berry,” called sassamenesh by the Algonquin and ibimi by the Wampanoag and Lenni-Lenape, was used for dyes and medicinal purposes by Native people up and down the Eastern Seaboard. Some tribes smashed the fruit with meat or fish and dried the mixture, rendering it preserved and portable.

Later, after European contact, sailors leaving the East Coast found they could fend off scurvy if they ate the vitamin C-rich “craneberries” every so often. Today, Massachusetts is the second most productive cranberry state in the United States after Wisconsin, growing over 100,000 tons of the fruit each year—the most significant agricultural product produced in the state, with the crop worth about $100 million annually.

(See how the cranberry business stacks up, in charts)

Their habitat in both states was formed by advancing glaciers, which carved hollows into the hard bedrock. When the glaciers retreated, the hollows filled with bogs—soggy, plant-rich, often sandy, acidic lowlands.

On the edges of the bogs, cranberry plants thrived. They adapted to plenty of water, harsh winters, and mild summers.

Water, rather than wind or wildlife, spreads their seeds: When the fruit ripens and falls off the vine, it floats away, buoyed by tiny air bladders near its core, washing up on a new marshy edge where the seeds can establish themselves.

During the chilly northern winters, the plants sink into a protective dormancy. Somehow—scientists still don’t know exactly how—the plants track the hours of cold they experience. That count determines when they go to sleep in autumn and when they power back up in spring: They require at least 70 chilly days, between 32 and 45 degrees Fahrenheit, in order to bud correctly.

“The plants depend on having that annual cycle of cold winter and dormancy,” says Libby Ellwood, a biologist who studies how climate change is affecting plants. “That’s how they know spring has hit.”

The plant is also fussy about warmth; too much summer heat and the leaves and fruit will scorch. The tiny buds for next season’s fruit show up in the middle of the previous summer, while this year’s ripening fruit is still on the vine. That means both are vulnerable to hot spells—so one intense summer heat wave can wreak havoc on multiple harvests. And if it's too hot and dry, the fruit can “scald," getting so overheated that it sometimes almost cooks in its skin.

Year-round changes

Every year now seems like it holds some record-breaking event, says Brian Wick, the executive director of the Cape Cod Cranberry Growers Association. “It’s the hottest this, the driest that. Extremes are no longer anomalies but are becoming the expected.”

Across Massachusetts, in all four seasons, bogs like Eldridge’s have started to feel the impacts of climate shifts.

Summer is obvious. The state had its hottest summer on record this year. When it's above 90 or so, growers often use water to cool down the fruit, which is expensive and can be labor-intensive. This summer's heat, along with a severe drought, caused Eldridge and other growers plenty of consternation.

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Then there's harvesting time. Ever since cranberries were first cultivated, in the early 1800s, they’ve been harvested in September or October. Now, Wick says, “the season has shifted” he says—and it doesn’t necessarily come earlier, as you might expect. And the lack of cool weather in late summer and fall confuses the plants’ ripening process, delaying the arrival of the cranberry red tint that makes the berries appealing to buyers. Growers then have to wait for the color to develop, making the season longer than it used to be. “By the middle of September, harvest was usually going. Now we’re getting into October” or even later, Wick says.

Changing conditions in other seasons also mess with the fruit’s success. The kind of cold cranberries need used to happen each winter without fail, but winters are becoming less consistently cold. It’s not game over yet, but a time is approaching when the chill hour requirement may be hard to hit, says Katherine Ghantous, a biologist at the University of Massachusetts’ Cranberry Station.

And less winter ice stymies other important measures for the plants. Growers often flood their bogs during the winter, primarily to keep the temperature stable around the vines. But every few years, they drive out onto the ice and sprinkle on a layer of sand. When the ice melts, the sand settles smoothly onto the plants below. “Sanding” stimulates new roots to grow and can help ward off pests by burying harmful insect eggs and fungal spores. Now, though, ice thick enough to drive on forms only rarely, forcing the growers to sprinkle sand by flooding the bog and sprinkling sand from using expensively-rented mini-barge or walking across the vines, sometimes damaging them. Neither works as well.

Frost fears

Ellwood and her colleagues dug up records spanning the 1980s to 2011 from a cranberry grower in Carver, Massachusetts, about 40 miles as the crow flies from Eldridge’s bog. The grower had kept careful records of when plants had popped out about 10 percent of their flowers each spring—the point at which the grower would start spraying fungicide.

Warmer springs cause the plants to flower about two days earlier for each degree warmer the average May temperature is. Springtime temperatures in Massachusetts vary a lot from year to year-- so it’s not like every year the plants flower earlier and earlier. But very warm springs, like 2010, pushed the flowering time up by at least two weeks, and these are more likely to come more frequently in the future, says Ellwood.

Early emergence can endanger the flowers, because just a small hit of frost, more likely to happen early in the New England spring, can destroy them and ruin a year’s crop. To protect their plants, growers often monitor temperatures at their bogs 24 hours a day during frost season, sleeping in their trucks or trailers nearby and waking up every few minutes to check the conditions. If the temperature gets close to freezing, they’ll quickly turn on sprinklers, dousing the plants with a light coating of water. As the water freezes, it gives off a tiny burst of heat—warming the nascent buds and leaves and encasing them in a protective, fragile sheath of ice.

But as seasons stretch, the frost risk extends too. If the buds are out early in spring, or fruits still on the vine in fall, and even a day of frosty weather descends on the region, the crop can be damaged. The Cranberry Station even has a system to help growers predict frost danger, using temperature, dewpoint, and other inputs. But it was only designed to work from April 15 to the end of October. At the behest of growers who’ve seen the changes firsthand, says Peter Jeranyama, a plant physiologist at the Cranberry Station, he’s re-tooling the window the predictor can work in, adding a full two weeks in both spring and fall.

Climate-induced confusion

The Blue Hill Meteorological Observatory, south of Boston, has been tracking air temperatures for over 130 years—the longest-running observational record in North America. Since 1885, the average annual temperature there has increased by 4 degrees Fahrenheit (2.2 degrees Celsius), well above the global average of about nearly 2 degrees F. Climate models point to even more warmth in the future. By 2050—within the range of a 30-year mortgage—the Northeast as a whole is projected heat up by 4 to 5 degrees F above preindustrial averages, according to the 2018 National Climate Assessment; at the rate Blue Hill and environs are going, they could feel even more.

Warming doesn’t always have a straightforward effect, but some things in the plant world are pretty linear: Hotter temperatures are fairly neatly correlated with earlier flowering times.

In the not-too-distant future, Ellwood says, the biggest concern is that cold-adapted plants like cranberries that rely on that winter dormancy period to cue their yearly cycles like flowering “might not be able to know to flower at all, because the seasons have become so confusing.”

Other changes are more complicated but no less impactful. Shifts in precipitation, for instance, are progressing rapidly in the Northeast. For each degree Celsius the atmosphere warms, it can hold 7 percent more water. That means precipitation events are getting more intense.

This year, for instance, the region has been in a record-breaking drought. But a few major storms dumped inches of water at once. Overall, the total rainfall is only slightly below normal—but “plants can’t use 5 inches of rain that falls in five hours,” Eldridge says ruefully, mostly because that deluge can’t be absorbed by the land.

In theory breeders might develop a new, more climate-proof variety of cranberry to replace the current plants. The problem is cranberries are perennials, and growers can’t afford to replace them often; some vines on the Cape are over 100 years old.

For many growers, climate change isn’t yet top-of-mind concern. But to some, like Eldridge, its influence is becoming more and more apparent. In some ways, that's an opportunity, says Brian Gareau, a sociologist at Boston College who has studied the ways growers think about climate change. "It's a tight-knit community," he says, which means "the more awareness is raised, the more it can spread." Casual conversations between growers (Eldridge has a network she chats with, including one colleague who "speaks cranberry fluently"), communications from the Growers Association, and chats with the Cranberry Station all shape the ways growers respond to climate challenges.

Jeranyama says there’s plenty of flexibility left in the system; the plants have faced other weather-related stresses in their evolutionary past and have the capacity to adapt, to a point. And growers can use clever tricks to temperature-control their bogs, like wetting them down at strategic moments (evaporating water sucks up excess heat and can cool the surface of the bog; freezing it releases heat and can warm the bog by 10 to 20 degrees Fahrenheit for a short period). But it takes work, and money, to adjust.

That means it’s now time for growers and researchers to start thinking ahead, says Wick. Today, “the farthest south you can grow cranberries seems to be New Jersey,” he says. “But by 2100, Massachusetts will have the weather of New Jersey or somewhere farther south. And then what will we do?”