Real-Time Cold Hardiness Monitoring
Critical temperatures for wine and juice grapes are determined using a method called “differential thermal analysis” as described by Mills et al. (2006) (PDF). These data are updated approximately weekly from mid-October through mid-April. Data is collected from buds and canes (node positions 4-7) on mature vines grown at the WSU Irrigated Agriculture Research and Extension Center (5 miles north of Prosser, WA) and from nearby commercial vineyards.
This information is provided as a service by WSU with partial funding from the Washington Winegrowers Association through the Washington Wine Industry Foundation and the Washington State Concord Grape Research Council. WSU is not responsible for any damage or loss resulting from the use or misuse of this information.
Click on the variety name below to see the most recent graph of cold acclimation through the season.
Interpreting the Graphs and Table
BUD10 is the temperature at which 10% of the primary buds will be killed; BUD50 and BUD90 refer to 50% and 90% bud damage, respectively. PHL10 is the temperature at which 10% of the phloem (bark) is damaged or when cane damage is starting. XYL10 is when phloem damage is complete and xylem (wood) damage is starting. This would be considered severe cane damage. Grapevines can survive more than 50% phloem damage and still be productive. When xylem becomes damaged, grapevine productivity and survival can be compromised.
If the temperature lines in the graph (top two blue lines) cross over the critical temperature lines for buds, then damage has likely occurred. Please review the Resources in the right navigation bar for information on managing cold-damaged vineyards.
Now that we are at or approaching bud break, we will not be able to run exotherm analysis in grapes any more. In previous years we have included the critical temperatures for several different varieties during the period leading up to bud break. Since every variety responds differently to cold, this should be used only as a rough guideline.
- Cabernet Sauvignon at first swell sustained no damage down to 25 F.
- Merlot at full swell showed slight damage to the buds, phloem, and xylem at 25 F. More serious damage to the phloem and xylem occurred at 23 F.
- Chardonnay at budbreak showed slight damage to the buds and phloem at 27 F. More serious phloem and xylem damage occurred at 25 F. Buds were seriously affected at 24 F.
Washington State University has developed a Cold Hardiness Model to predict grapevine cold hardiness anywhere temperature data is available. It is available both as an EXCEL sheet (to enter your own weather data), or via AgWeatherNet (for WA locations).
More information on Cold Hardiness Modelling
Cold Hardiness Modelling
- WSU Grapevine Cold Hardiness Model webpage.
Preventing Cold Damage in Grapes:
- Protecting Grapevines from Winter Injury (PDF)– PNW #603E
- 2012 USDA Plant Hardiness Zones – The best way to prevent cold damage is to not plant in areas prone to it. Use this interactive map to determine if your area is at high risk.
Assessing Cold Damage in Grapes:
- Assessing and Managing Cold Damage in Washington Vineyards – WSU #EM042E
- ESPAÑOL – Evaluación y Manejo del Daño por Frío en los Viñedos de Washington
- Winter Freeze Damage and Vine Fruitfulness (PDF): Why does cold damage impact yield? – WSU Whitepaper
- Anatomy of Winter Injury (PDF) – Cornell University
Responding to Cold Damage in Grapes:
- Effect of Pruning on Recovery and productivity of Cold-Injured Merlot Grapevines – AJEV 2007 58:351-357
- Vine and Vineyard Management Following Low Temperature Injury – ASEV 2000 Cold Hardiness Workshop