The sudden cold snap in the country has caught everyone a bit by surprise and Eastern Washington has not escaped the artic weather. We are seeing some nights below 0F and obviously at that temperature we start to worry about winter injuries on our vines.
The cold can kill the buds that we need in order to grow a new canopy in the spring and it can damage the trunks by killing the phloem or the xylem that carry the sap (more on that later if you don’t know what I am talking about). So how low of a temperature can our vines take before we get injuries that would compromise our yields? Well, the Yakima Valley farm extension of Washington State University has a method forecasting the cold hardiness of buds and vascular system (phloem and xylem) of each grape varietal in Eastern Washington. At this point, it looks like our Riesling bud are safe until -7F but would be 90% destroyed if we get below -12. The concerning area right now is the phloem cold hardiness which is rated at 0F (the xylem is OK until -14F). So it looks like that we should expect some phloem damage but we should be fine with bud and xylem damage.
The Phloem is most important because it carries the sap in the middle of the trunk and does not renew every year unlike the xylem (the xylem makes those rings every year on the plant). If the phloem on our vines gets damaged we will have to cut them to the ground and grow the vines back from the roots (which is fine since we are on our own roots with no rootstocks). Usually, when we cut our vines down we expect a shorter crop. Stay tune for more information.