With a mild winter and spring in Marlborough, the vines seem to be getting a bit ahead of themselves. The buds have started to burst, particularly for chardonnay and some gewürztraminer, varieties that are always early to show their spring colours. Whilst on the one hand, we welcome another sign of spring, along with the daffodils, tulips and freesias, on the negative side, these plants become highly susceptible to frost damage so vineyard management is on frost alert.
Over the winter, frosts are not a problem, the vines are dormant and untroubled by frost. The green shoots however, are very frost tender and so once buds have burst growers are on the alert for potential frosts and many take action to prevent damage.
Frosts in Marlborough are generally radiation frosts occurring on cloudless, still nights. Cold air is heavier than warm air and as the ground radiates heat during the night, cold air is trapped at ground level, with significantly warmer air above. So the solution to the frost is to mix these air layers up, bringing the warmer air down to ground level. Easy. There are several ways to do this. The earliest form of frost protection was smudge or frost pots – small burners that run on diesel and produce some heat, but more importantly set up convection currents that mix the air layers. A second option is the frost fans up to 15m tall and rotating at maybe 2000rpm.
Fans usually have a generator at the base and are set to come into action automatically as the temperature drops close to freezing. The big disadvantage with these is the noise, although improved blade design has reduced noise levels. A third option is to fly a helicopter over the vines, keeping it in the warmer layers which are pushed down to displace cold air near the ground. The delightfully named “Tow and Blow” is a mobile ground based fan alternative.
Frost fighting is perhaps technically simple, but it is expensive, so research continues into vineyard management alternatives. Future options may include having a small current running through a wire to produce a small amount of heat and blowing warm air into the vineyard through the irrigation hoses. Watch this space! Or join us on a Marlborough wine tour to hear the latest updates in frost fighting.