Climatic condition at one temperature below 0 ° Celsius or 32 ° Fahrenheit. In general, the air temperature is measured at a height of 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 . Basically, a distinction is made between radiation frost and adjective frost . Radiation frost occurs on dry, clear nights with no wind, when lack of clouds, mist or haze escaping from the ground or the plant tissue heat escapes unhindered into the atmosphere. The coldest (and heaviest) air sinks to the bottom and collects on the surface, preferably in low-lying hollows. The adjective (aka "attached") frost is caused by the inflow of already cooled air from other places. This can be done from very distant areas such as through a long valley.
Already when creating the vineyards can be achieved by appropriate measures a certain protection. A hillside, from which the cold air flows into deeper areas (air drainage), as well as high education forms are of great advantage. Low-lying and flat areas are the most vulnerable. A frost control in the vineyard is done by so-called wind machines (or even by helicopters), with which a mixture with the warmer in the upper layers of air artificially induced (see also under wind ). Also warming smoke ovens, large heaters and similar means are used. Artificial irrigation can be used to directly heat the vines and the soil, because when the water freezes, heat is released or a thin layer of ice on plant parts additionally forms a protective sheath.
In the northern hemisphere frost is generally referred to as late frost in the spring ( maifrost in the month in question) and early frost in late summer / autumn. In the course of the annual growth cycle is the occurrence of frost for the Rebstock different dangerous. In the northern part of Europe usually starts in April the expulsion in which the boys shoots are particularly susceptible to late frosts. Even temperatures as low as minus 1 ° C at the level of the vines usually cause damage. Especially short-term temperature changes are dangerous, if after a warm spring already the budding has occurred and then a late frost occurs. 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. Traditionally frost-prone areas include chablis and Champagne; in 1991, one third of the crop was destroyed. By a late one pruning the shoot-out time can be delayed slightly (1 week to a maximum of 10 days).
The resistance of the vine depends on the grape variety and above all on the wood maturity. The documents are mostly cold-resistant than the tops of the species Vitis vinifera, In areas prone to frost, it is recommended to stock with late-propagating grape varieties, for example Cabernet Sauvignon. Clairette. mazuelo. Monastrell. Müller-Thurgau. Trebbiano Toscano. Riesling. Sauvignon Blanc and Sylvaner, For example, endangered varieties are particularly at risk Chardonnay and Pinot Noir (but these are the best in cooler areas). Grape varieties in cold areas with frosty winters have one resistance (Resistance) developed against frost. In the breeding This is also one of the main breeding objectives of new grape varieties. That's what the froze-resistant Asian species like to be Vitis amurensis used. A well-known breeder of froz-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 danger of late frosts generally applies to the so-called Eisheiligen (11 to 15 May) as spellbound, then they are extremely rare. In late summer and early fall, early frosts can cause more or less damage. Even a few degrees below freezing point can end the vegetation and Defoliation to lead the vines. But it is of crucial importance, whether the frosts before or after the vintage occur. If the grapes have already been harvested, that's usually not so bad. Whether a damage occurs in still unharvested grapes, depends on the maturity state (see also under maturation ).
In unripe grapes, the harvest can be significantly decimated, the wines can thereby also a Frost taste respectively. The fully ripe grapes, on the other hand, practically do not harm frost. Temperatures from minus 7 ° C are for the production of Eiswein even unconditional prerequisite, but the grape harvest does not take place until November at the earliest. During the Hibernation However, the vines are relatively insensitive and survive usually short periods of cold to minus 25 ° C and more, if not preceded by several warm days that have the juice rise. For high altitudes and high latitudes, winter frost can cause considerable damage. See also the keywords under this topic irrigation. soil type. drought. hail. climate and precipitation,
Weingarten: Picture of Gerd Altmann on Pixabay
Late frost: André Mégroz Switzerland
Frühfrost: By Bauer Karl - Own Work, CC BY 3.0 at , Link
Winter Frost: By Bauer Karl - Own Work, CC BY 3.0 at , Link