Climatic condition at one temperature below 0 ° Celsius or 32 ° Fahrenheit. In general, the air temperature is measured at 1.25 meters above the ground; at this altitude, the temperatures are always slightly higher than on the ground. In meteorology, frost at the level of the ground is called ground frost . A basic distinction is made between radiation frost and adjective frost . Radiation frost occurs on dry, clear nights with no wind, when the heat radiated from the ground or plant tissue escapes unhindered into the atmosphere due to missing clouds, fog or haze. The coldest (and heaviest) air sinks to the ground and collects on the surface, preferably in deep hollows. The adjective (meaning "attached") frost arises from the inflow of cooled air from other places. This can be done from very distant areas, such as through an elongated valley.
A certain level of protection can be achieved by taking appropriate measures when the vineyards are being created. A hillside, from which the cold air flows into deeper areas (air drainage), as well as high education forms are of great advantage. Deep and flat areas are most at risk. Frost control in the vineyard is carried out by so-called wind machines (or even by helicopter), which artificially mix with the warmer air in the upper layers (see also below wind ). Warming smoke ovens, large heaters and similar means are also used. Artificial irrigation can directly heat the vines and the soil, because when the water freezes, heat is released or a thin layer of ice on plant parts also forms a protective coat.
In the northern hemisphere, frost is generally referred to as late frost in the spring (also May frost in the month in question) and early frost in late summer / autumn. During the course of the year growth cycle is the appearance of frost for the Rebstock different dangerous. In northern Europe it usually starts in April expulsion in which the young shoots are particularly susceptible to late frosts. Temperatures as low as minus 1 ° C at the height of the vines usually cause damage. Short-term changes in temperature are particularly dangerous if they have already sprouted after a warm spring and then show late frost. Interestingly, this is not so common in the cool growing areas, but rather in warmer areas and is, for example, in the US state Texas feared. Areas that are traditionally at risk of frost include: chablis and Champagne; in 1991 it destroyed a third of the harvest. By late pruning the budding time can be delayed a bit (1 week to a maximum of 10 days).
The resistance of the vine depends on the grape variety and especially on the maturity of the wood. The documents are usually more cold resistant than the tops of the species Vitis vinifera, In areas prone to frost, planting with late-growing grape varieties is recommended, for example Cabernet Sauvignon. Clairette. mazuelo. Monastrell. Müller-Thurgau. Trebbiano Toscano. Riesling. Sauvignon Blanc and Sylvaner, For example, the early growing varieties are particularly at risk Chardonnay and Pinot Noir (These are the ones that thrive best in cooler areas). Grape varieties in cold areas with hardy winters have one resistance (Resistance) developed against frost. In the breeding new grape varieties, this is also one of the main breeding goals. For this, the frost-resistant Asian species will be happy Vitis amurensis used. A well-known breeder of frost-resistant varieties was the American Elmer Swenson (1913-2004).
Winter frost below 18 ° C leads to damage to the main eyes, then to the destruction of the secondary eyes and also the trunk. The risk of late frosts generally applies to the so-called Eisheiligen (May 11th to 15th) as banned, after that they are extremely rare. In late summer and early autumn, early frosts can cause more or less damage. Just a few degrees below freezing can end vegetation Defoliation of the vines. But it is crucial whether the frosts before or after vintage occur. If the grapes are already harvested, it is usually not that bad. Whether damage occurs to still un harvested grapes depends on the ripeness (see also under maturation ).
With unripe grapes, the harvest can be significantly decimated, which means that the wines can also be one Frost taste exhibit. Frost, however, practically does no harm to fully ripe grapes. Temperatures from minus 7 ° C are for the production of Eiswein even an unconditional requirement, although the grapes are only picked in November at the earliest. During the Hibernation the vines, on the other hand, are relatively insensitive and usually survive short cold periods down to minus 25 ° C and more, if not preceded by several warm days that have allowed the juice to rise. Winter frost can cause considerable damage to vineyards at high altitudes and in high geographical latitudes. See also on this topic under the keywords irrigation. soil type. drought. hail. climate and precipitation,
Weingarten: Image by Gerd Altmann from Pixabay
Late frost: André Mégroz Switzerland
Early frost: By Bauer Karl - Own work, CC BY 3.0 at , Link
Winter frost: By Bauer Karl - Own work, CC BY 3.0 at , Link