When frost has been predicted, growers should take note of their vineyard’s growth stage so a strategy can be developed. Vineyards that have not yet begun to break may not require special attention. When green shoots are longer than six inches, soils may need to be prepped in advance of cold weather. Table 1 shows the relative susceptibility of grapevine tissue at different growth stages and critical temperatures.
Table 1. Frost damage to various growth stages of grape.
|Growth Stage||Critical Temperature*|
|Buds with wool (eraser stage)||< 26˚F|
|Shoots < 6” in length||< 31˚F|
|Shoots > 6” in length||< 32˚F|
*Critical temperatures are based on research under controlled environments. Vineyard characteristics (location, cultivar, etc.) may increase or decrease susceptibility to frost damage. These values should only be used as a point of reference when developing a frost protection program.
In order to minimize damage caused by frost, vineyard soils should be prepared for maximum heat absorption during the day and release at night. Optimal conditions include soils that are free of vegetation, firm in texture, and moist. Moist dark soils improve their ability to absorb heat during the day and radiate it at night as ambient temperatures drop. Soil texture will also have an impact on heat absorption.
Vineyards planted to sandy soils are more prone to frost damage because they lack the ability to retain water. Additional water may be needed if winter precipitation has not been adequate to maintain soil moisture. Prior to a predicted frost, the goal should be a uniformly distribute irrigation, that allows for maximum heat absorption.