Bringing in the May

Back in March, as always, we took cuttings of forsythia and “forced” them to bloom indoors. It sounds almost unkind – but tricking plants into doing what we want is fundamental to horticulture. After decades, the old Russet tree still tries to reach for the sky, and we ruthlessly cut off all those vertical shoots. The grape vines tolerate more mutilative pruning, and every year they throw fruit as if this is their last chance. All the forsythia has to offer us is its beauty, though for pollinators it likely provides an early source of nourishment when few others are on offer. The bush receives no care or tending, and still grows like stink – replacing the repeated cuttings that lend some bright-yellow cheerfulness to our kitchen, as a promise that spring will eventually come for real.

But even now, with the new season showing its colours across the landscape, there is a degree of uncertainty – or perhaps several degrees. Can spring be trusted? According to one nugget of folk wisdom, we should expect three more snows after the forsythia blooms. For those who mark the calendar when they first hear peepers, there is another old adage that says frogs will look through ice twice. (We can assume that whoever invented these cute prognostics was not actually betting the farm on their accuracy.)

Historically, there have been many celebrations oriented toward welcoming spring and ensuring a good growing season. May Day, with its garlands and ribbons and dancing, was eventually industrialized, morphing into a workers’ holiday. (It became associated with the Haymarket Riot in May of 1886, when police clashed with strikers at the McCormick Harvesting Machine Company in Chicago – but soon afterwards, both the U.S. and Canada replaced it with a September holiday known as Labour Day, whose proletarian flavour was eventually much diluted.)

In northern Europe and Scandinavia, many people still whoop it up on April 30, which is Walpurgis Night (named for Saint Walpurga, an eighth-century nun who became abbess at Heidenheim, a monastery in Germany). The festivities include bonfires – a feature dating back to pagan times, when it was an end-of-winter ritual associated with cleansing and fertility. Some sources suggest that burning bones was part of the tradition. (The word “bonfire” is derived from “bone fire.”) That would have been a way to dispose of household refuse, with the added benefit of producing foul-smelling smoke to drive away demons and diseases. Afterwards, the ashes were spread on cropland – a practice that has agronomical merit. As for the celebrants themselves, all this outdoor carousing was known to bring an uptick in human fecundity – and through the centuries, May Day retained a whiff of the salacious.

On this holiday, the gathering of flowers and foliage was known as “bringing in the May.” But in northern climates, there has always been the question of whether May will stay. Spring can trick you into making some bad decisions – like planting too early. And as any orchardist or viticulturist will tell you, fruit crops are extremely susceptible to frost damage at this time of year.

Dr. Harrison Wright, a plant physiologist at Agriculture and Agri-Food Canada’s research centre in Kentville, N.S., tells me this is the paradox of climate change: farmers are keen to take advantage of increasing temperatures, but seasonal weather patterns are unreliable. “Climate ‘weirding,’ they call it. It has to do with the variability.”

Wright says warmer weather has allowed for expanded commercial production of relatively new crops. “We have data going back to 1913, and in that time our growing season has increased by approximately 40 days. That’s from the last spring frost to the first fall frost. That’s pretty huge, and that’s why we can now grow some of these grapes,” he says. “And the heat that we have, in growing-degree days, at the Kentville site it’s about 27 percent more.”

Unfortunately, crops thrive or perish on the basis of actual weather, not statistical averages. In 2018, Nova Scotia was hit with a particularly bad spring frost, when temperatures plunged on the night of June 4. “I think it would be safe to call it the worst we’ve had for a couple generations,” says Wright. “The Christmas tree producers got hammered, the lowbush blueberry producers got hammered, apples got hammered, and wine grapes got hammered.”

At the one-hectare research vineyard that Wright oversees, the damage was severe. “It was in the mid- to high-20s for several days the week before, so the plants had really taken notice. They were really growing quick, they were really full of water, and that makes them very sensitive to freeze damage, when you have that young tissue.”

Part of the irony is the fact that short-season, winter-hardy varieties actually suffer the worst from this kind of weather event. “It’s kind of counter-intuitive, but they got hit even harder, because they were jumping at that heat and they were excited that it was warm, so they were that much further along,” says Wright. “Each bud had already broken, and probably 99 percent of them were killed. And on some of the early ones, all the inflorescences – the fruit – had come out, and they were also killed because they were very sensitive. So those vines essentially had no crop that year; it was less than a tenth of what it would normally be.”

Nonetheless, Nova Scotia’s wine industry is booming, producing almost 1.9 million litres annually – which is why research efforts are being directed toward helping vineyards manage weather risk. To this end, the centre at Kentville recently purchased a trailer-mounted frost fan, which can be used to disperse pockets of cold air that sometimes settle to the ground on a still night. The phenomenon is called “radiation frost,” or “temperature inversion,” says Wright. He points out that it can also be addressed, to some extent, by removing physical impediments such as a treeline at the bottom of a slope, to allow that cold air to drain away. Even keeping the grass well mowed can make a difference, by promoting better airflow.

Frost fans are used in cool-climate fruit-producing regions around the world, but they are not common in the Maritimes. The one at Kentville is a relatively compact model from a New Zealand manufacturer called Hydralada. Its five three-foot blades are direct-driven by a 24-horsepower diesel engine, on an articulated boom that can easily be lowered for transport.

“We’re hoping that will give us some versatility to do research with it, to move it around and try some different things,” says Wright, who usually programs the machine to operate when temperatures drop to about 4 degrees C. He notes that large models, usually installed on a concrete platform, could agitate neighbours as well as cold air. “With a 250-horsepower engine that powers up at 2 o’clock in the morning – and the fan itself makes a fair bit of noise – not everyone’s happy about that. You get that oscillating sound,” he says. “Our fan is pretty small; it’s only meant to protect a few acres. Some of these big fans are meant to protect 10 to 20 acres.”

Radiation frost can also damage nearly-ripe fruit in the fall, but crops are most vulnerable at the beginning of the season. “The plants are getting mixed messages,” says Wright. “They’re being told to start growing, and then Mother Nature decides it’s not going to be spring after all, and slams the door.”

In some wine regions, a common remedy is to fly helicopters over the vineyard – which could be perceived as even more anti-social than a loud fan. Alternatively, dozens of fire pots may be arrayed up and down the rows, staving off frost as they burn all night. The effect is eerily beautiful. More than anything, it looks ritualistic – like an appeal to the gods for meteorological mercy. DL