Frost and frost protection

[The following page refers to conditions and practices typical in Central Otago (New Zealand). While much of the material is general in nature, care must be taken when applying it to other regions as climatic conditions and cultural practices are likely to differ.]

While there are two dominant types of frost (radiation frost and advective freezes) the major cause of tissue damage in grapevines are spring and autumn radiation frosts. These frosts typically occur overnight when cold southerly airflows are followed by clear and still conditions (anticyclone moving onto the country). Long wave length radiation released into the atmosphere results in the rapid cooling of plants, soil and trellising and this in turn cools the adjacent air. This cold air then settles towards the ground and begins to flow toward lower elevations collecting in “frost pockets”. While radiation frosts are more severe early (October – mid November) and late in the growing season (15th April onwards), vines are particularly susceptible between 15th November – 1st December when temperatures of only -0.5˚C can cause tissue damage to the new growth. Before this time frosts can generally be managed by removing dead tissue and allowing secondary shoots to form the canopy. At the other end of the season, late spring frosts severely reduce the quality and quantity of the crop and in many instances will result in the loss the of whole crop. While early autumn frosts are not common, severe events in March/early April will destroy the leaf canopy and result in the vines not being able to ripen their crop. Mild autumn frosts (no lower than -1.5˚C) will cause leaf damage but do not significant impact on ripening.

Wind machines and overhead sprinklers

The main types of frost protection used in Central Otago are wind machines (including helicopters) and overhead sprinklers (video).

Both methods have their limitations and careful consideration of the site is necessary to select the most appropriate method.

The usefulness of wind machines and helicopters is limited to instances where warm higher-level air can be mixed with lower freezing air to increase the temperature at vine level. If no inversion exists then this method will not work. Overhead sprinklers are good during spring, however, dumping large amounts of water on vines at harvest, especially on heavy soils can be detrimental to grape quality and restrict access of vineyard equipment. Overhead sprinklers are difficult to manage when bird netting is used. Return to site selection