Protection of the apple trees: Fire & Water

When another frost period looms, farmers are already studying weather forecasts and temperature predictions the evening before, allowing them to estimate whether a frost night is approaching. Orchards in low-lying areas – such as those along the Adige River – are more prone to frost than those on the slopes, as even a few meters in elevation can make the crucial difference between freezing and non-freezing temperatures.

A tightly woven network of 119 weather stations provides farmers with real-time data on local temperature, humidity, and wind direction. When temperatures approach critical thresholds (around -5°C during early vegetative growth and 0°C during blossom phase), a frost alarm is triggered – sometimes at midnight, sometimes as early as 4 a.m. In the past, so-called frost wardens would rush from thermometer to thermometer and sound the warning with a long siren blast. These days, farmers still alert one another by phone, but many now rely on automated notifications sent directly to their smartphones, including through various app providers.

As soon as the alarm goes off, farmers leap out of bed and rush to their orchards to activate the frost irrigation. Using tractors or motors, they start the pumps that draw groundwater and spray it evenly over the trees and blossoms using circular sprinkler systems. The water forms a thin layer of ice around the flowers. As it freezes, a physical reaction occurs: the process of crystallization releases heat (known as latent heat of fusion), which paradoxically protects the blossoms from the extreme cold.
Once morning temperatures have stabilized a few degrees above zero, the system is shut off and the water seeps back into the groundwater supply.

A beautiful side effect of frost irrigation: when the morning sun hits the icy coating, the entire valley sparkles and shimmers like something out of a fairy tale.

In areas where frost irrigation isn’t possible, such as on even slightly sloped terrain where water can’t be pumped, farmers turn to “candles” to get their blossoms safely through the frosty night.This method dates back to ancient Rome and was first adopted in South Tyrol mainly in vineyards. Today, it has also proven effective in apple orchards. Small fires, placed at regular intervals between the rows of trees, gently warm the surrounding air by about 2 to 3 degrees Celsius, just enough to make a difference. The smoke created also helps by causing slight air movement and turbulence, which disrupts the settling of cold air.

South Tyrol was a pioneer in frost irrigation: In 1949, a farmer from Terlano built the first frost irrigation system using old pipes and war materials, which was put into operation in 1950 and later served as a model.

But since we’re in South Tyrol, of course there’s also a legend about how frost irrigation was really invented: One evening, a farmer set out to switch off the irrigation in his orchard but met some friends along the way and was persuaded to have a glass of wine. Naturally, one glass led to another, and soon the entire night was spent celebrating and drinking in the inn. Meanwhile, the temperature dropped sharply, and on his way home, the farmer was shocked to see icicles hanging from his apple trees. It wasn’t until harvest time that he noticed his trees were full of apples, while those of the other farmers were nearly empty. That’s when it occurred to him that it must have been that fateful frost night that made the difference, and so frost irrigation was born.