Frost is a weather phenomenon that occurs in the atmosphere when surface temperatures drop to 0°C, causing the formation of frost. When temperatures fall, the wind calms, humidity increases, and moisture in the air condenses, freezing on plant surfaces, creating a layer of white ice crystals, known as hoarfrost or white frost.
Frost can cause significant damage in agriculture, but not all crops are affected the same way. While some plants die from white frost, others may survive. On the other hand, black frost is more harmful. It is called “black frost” because it does not display the typical white crystalline frost. Instead, plants have already died when the temperature drops below 4°C, causing water inside the plants to freeze, the air lacks moisture, and the wind is dry and cold, leading to dehydration and death of the plants.
When frost occurs, the temperature at the ground level often differs from that below the canopy, sometimes by 4-5°C. If the temperature under the canopy drops below the critical threshold, it disrupts the flow of sap in plants or causes it to freeze, resulting in the death of leaves and branches due to the lack of nutrients.
Each plant species has different tolerances to cold. For example, maize tolerates temperatures as low as 9°C, coffee plants can withstand 6°C, and pepper plants can handle 8°C. Below these thresholds, plants stop growing, and prolonged exposure can lead to death without visible frost.
In Vietnam, it was reported that frost damaged 700 hectares of coffee in Lam Dong, although meteorologists confirmed there was no visible frost in the southern regions of Vietnam, and the local community in Lac Duong, Lam Dong, did not witness white frost.
Frost Damage to Coffee Plants in Brazil
When the temperature drops below the critical threshold (around 2°C), the sap in coffee trees can freeze, even if frost doesn’t appear on the surface due to dry air. Brazil’s winters are often referred to as “dry winters” because of low humidity. After a frost night, sunny days with intense radiation can cause the coffee branches to dry up quickly due to the high temperature fluctuations. However, shaded coffee plants experience higher surface temperatures compared to those without shading, thus minimizing the damage.
The most affected areas are the coffee-growing regions in southern Brazil, specifically in the Serra da Mantiqueira mountain range that spans São Paulo, Minas Gerais, and Mato Grosso do Sul, with some other regions in Santa Catarina and Paraná states. Cold air masses from the polar region move into these areas, leading to frost, and the likelihood of frost occurrence depends on the intensity and duration of the cold period.
Frost typically occurs in clear skies with low temperatures. Farmers can predict frost conditions by observing clear, cool nights during autumn and winter months, especially in the months of July.
Currently, regions frequently affected by frost no longer grow coffee. Coffee plantations in the primary coffee-growing states have shifted to altitudes below 800m, away from areas prone to high frost frequency. Frost generally only occurs for about three months, mainly in July.
After more than 23 years without frost damage, Brazilian coffee farmers have expanded their cultivation areas, resulting in many reports of frost affecting young coffee trees in their early stages or newly established plantations. Brazilian agronomists are experimenting with frost protection methods, primarily in coffee nurseries.