Frost protection
Once vines are fully dormant they are hardy and can tolerate quite severe frost, but temperatures below - 0˚C will cause damage once the vine buds have burst.
| Method | Comment |
|---|---|
| Site selection |
This is the most effective method. Avoid frost hollows where cold air collects. |
| Cold air drainage | Do not create a frost pocket by planting a thick hedge or erecting a solid fence across a sloping site and thin existing hedges to allow cold air to drain away. |
| Height of pruning | The closer to the soil the greater the frost risk. High wire training (e.g. Geneva Double Curtain) can raise the height of buds out of the risk of ground frost. |
| Delay pruning | By delaying pruning until the buds on the tips of the vines start to burst. The buds closer to the head of the vine will be slower to break and the removal of the top growth with stimulate lower buds to develop and these will be a week or so later. |
| Soil condition | Frost risk will be reduced if the soil condition is such that heat can easily be conducted from lower layers. Therefore compact, damp and weed-free soils perform best if there is a risk of frost. |
| Polymer coatings | Young vines can be sprayed with a polymer coating (ANTI-STRESS) that provide some insulation and protect the shoots from desiccation. The vine easily grows through the thin polymer coat. |
| Fans/windmills |
These can mix the upper layer of warm air with the cold air layer closest to the vines (cold air sinks). Wind machines are available in two types:
Generally speaking, a machine providing 10 hp/acre will effect a temperature rise of one quarter the difference between the air temperature at 2 m and that at 15 m. |
| Heaters - Candles, burners, braziers heat from direct radiation and convection. | Effective, but can be expensive and can cause smoke nuisance. |
| Water sprinkling |
As the water sprayed on to vine shoots freezes, it releases a little heat, ensuring that the temperature of the shoot will never fall below 0ºC, even when the air temperature is as low as -9ºC. However this means that sprinkling must be continuous throughout a frost, starting as temperatures reach 1ºC and continuing until the risk of frost has gone. Water sprinkling can be automated and can be used as an irrigation system during the summer. This is not a method to use on a site that has poor drainage for to use overhead sprinklers during a frost that could last for 8 hours, a very considerable amount of water will be used (30,000 litres per hectare per hour). |
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