It seems that the risk of frost has increased in recent years due to global warming, which doe snot just warm but makes the climate more erratic and temperatures more extreme. Good news for the moderately temperate climate of Bordeaux where hotter drier summers have produced a string of good recent vintages (2015, 2016, 2018, 2020). But the negative side of this is that frosts have become more common right up until the end of the usual cycle – last year on 6th May.
Past Bad Frosts – 1956 is legandary with a very cold winter frost some minus 20 °C following a warm period when the sap rose from the roots into the vine foot and branches. It killed the vines. The last disastrous late spring frost before 2017 was 1991. It seems to be striking significantly every two years now now and a every year to a degree. Who would have expected the devastation again this year, 2021 some forty years on.
This year April 7th and 8th brought despair to vignerons (and other crops) right across France from Champagne to Cognac, Burgundy to Bordeaux as thousands of vineyards’ new growth was obliterated by frost (resulting in zero yield for harvest 2021). There may be some new growth and some secondary budding but this is a repeat of 2017 (if not worse) and few were able to harvest any grapes worth speaking of. Perhaps the wealthy vineyards expensive techniques were able to save their best vineyards but most who could afford creating smoke blankets from burning hay bales – they were no match for the frost with temperatures down to minus 5 in some areas. Hopefully insurance had been taken out, which involves a substantial expenditure each year. Many vineyards in lesser known areas (Castillon, Bourg, Blaye, Côtes de Franc, Graves, Satellites of St Emilion) who could not afford these payments and who played ‘russian roulette’, this year lost for perhaps for the last time.
With frost the later it strikes, the more damage it does as the vine has had a chance to bud, grow its first leaves and even buds that will become the flowers and fruit as in 2017. On 27 and 28 April when very warm conditions meant vegetation was 2 weeks ahead of ‘normal’ frost obliterated all vegetation and all possible yield so early in the cycle.
So how does one protect the vines from frost?
- Aeolian wind turbines and fans – expensive – some are permanent others you can wheel around to move air around and stop it settling
- Air heaters – some are permanent others you can wheel around
- Helicopters 1600€ per hour can only fly from 6am but this the coldest time when the sun comes up. Can do 10 hectares. They push the cold air around so that it does not sink down to the ground causing its damage
- Candles – usually they last 12 hours so normally can be used for two nights. Cost is 10€ each and you need around 300 per hectare. They do need to be lit and extinguished though.
- One can spray with water if you are set up for this via a sprinkler system like irrigation. The vine leaves are protected in their own frozen bubble. Bernard Defaix Chablis see photos below
- The most common is burning hay bales. The smoke causes a blanket which heats up the atmosphere. (better than burning rubber tyres like they used to!) You have to be aware of the wind direction and make sure the bales are in the right place. It helps if your neighbours do the same.
- Biodynamic producers spray the vines with valerian to give the vines some added fortification to survive themselves
- Another product that is sprayed is based on pectins from apples which is supposed to lower the temperature around the vines
- Electrical heating cables in Cognac and Southern England – costly alternative