This first week of April has been extremely stressful fo winegrowers all over France. Due to sunny weather and summer-like temperatures at the end of March, bud burst occurred in the vineyards. Unfortunately severe morning frosts occurred on April 6th, 7th and 8th,  with temperatures well below 0°C that destroyed a great part of the harvest 2021 - up to 95% according to some winegrowers. Some more freezing temperatures are due in the next few days so winemakers are getting ready to combat frost again. And they will have to hold out until the beginning of May. The coming weeks are going to seem very long... This phenomenon of morning frosts is not new but is becoming more and more frequent because of climate change. The absence of harsh winters is often synonymous with a return of the cold in April or early May, when the plants has already woken up. Several techniques allow winegrowers to cope with frost and try to limit the damage.

It is surely the method most people have heard of. It is the second most effective after water sprinkling (see below). "Bougies" are large candles placed in the vineyard, in the middle of the rows. They are lit during the night, before the temperature begins to drop. The goal is to warm up the atmosphere (+ 2 to 3 ° C) to prevent the buds from freezing. A minimum of 200 candles per hectare is needed and the colder it gets, the more you need  - 400 to 500 of them for temperatures between -6°C and -7°C. They require constant attention and can keep winemakers awake most of the night. They are put out once temperatures have risen above 0°C, after sunrise. This anti-frost solution requires a lot of staff and labor and remains among the most expensive: up to € 2,500 to € 3,000 per hectare, depending on the number of candles used. It is therefore impossible for winegrowers cultivating large areas to protect all their plots in this way. They therefore favor the best terroirs. This technique is used almost every year by the winegrowers of Chablis, a Burgundy appellation where spring frosts are extremely frequent. This critical moment gives surprising landscapes and magnificent shots for photographers.

This technique is the most effective and it also gives birth to amazing landscapes. The objective: to protect the buds with a thin layer of ice - this is the principle of the igloo, in which the temperature remains positive while it can be very cold outside. The water sprinkler system is triggered by a probe when the temperature drops below +1°C. When it freezes, the water sprayed on the vines forms a cocoon of ice and releases calories that protect the bud inside from the cold. It is necessary to maintain continuous watering, until the temperature rises above +3°C. One inconvenient: this technique requires having access to water in the vineyards, which is not the case everywhere.

The use of straw bales is the most rustic and the most tedious solution to resort to. The straw bales are placed collectively by the winegrowers around the plots that need to be protected. In this case, the desired result is not the production of heat, but of smoke, which will replace the cloud cover. Clouds prevent damage by blocking the sun's rays as the sun rises - this is the most critical time for buds, when the cold, combined with sunlight, burns out the buds. The straw fires are therefore lit just before the onset of sunrise. Some winegrowers also burn the old vines which were pulled up and the old stakes that were replaced during the winter - all means are good...

Antifreeze towers and wind turbines are used to stir the cold air that descends near the ground and the warmer air that rises. The mixture of the two helps to raise temperatures and prevent freezing. This therefore requires that the global temperatures are not too cold, otherwise there is only cold air (what we call black frosts, when the wind comes from the north or the east) and the technique is unnecessary or even harmful. If necessary, the winegrowers therefore supplement the use of anti-frost towers by lighting candles or fires on the plots to be protected. The most efficient wind turbines are however equipped with an integrated heating system: below a certain temperature, a sensor triggers the heating system, the heat produced at the foot of the tower rises and is dispersed by the blades of the wind turbine. A heavy investment for winegrowers: €43,000 on average, and no less than €25,000 for a portable wind turbine without a heating system. But the fixed towers, put in the plots that are regularly at risk, can cover up to 5 hectares. They are therefore often an investment shared between several winegrowers.