One day we are thinking about the risk of an early budbreak and now today I am happy the grapevine buds are safe and protected as the temperatures dip down into the teens. If the warm days have caused them to start deacclimating, they would be at greater risk of cold injury. Luckily, at least this week, the weather will keep them in a dormant state; cozy inside their protective bracts and hairs.
These compound buds are extremely important as they will produce the shoots that support and ripen the clusters in the coming vintage. If these buds are damaged, it can result in a loss of shoots and or crop.
At this time of year, the buds appear brown with occasional tufts of white epidermal hairs showing. As they go into dormancy, they lose water and become lignified. When they obtain maximum cold hardiness, the buds can resist temperatures down to around -8 to -10 degrees F.
The compound bud on a grapevine is a truly amazing work of biology. The compound bud really contains three buds (primary, secondary and tertiary) so this in itself increases the chance of survival for the vine. Within the primary bud, there are a number of primordia (growing points) protected inside. The compound bud can contain 6-10 leaf, 1-4 cluster, one lateral and several tendril primordia all compressed into this small inconspicuous bud. It is somewhat like an accordion.
In the spring the buds go from being in a dormant cold hardy state to active growth at which point all cold hardiness vanishes. Spring shoot growth bursts from these buds supported by carbohydrates and nutrients stored in the trunk and roots. The leaf primordia inside accounts for about two thirds of the total shoot grown that occurs by bloom. As they grow, it is like opening the accordion and creating space between each node that will contain a specific pattern of leaves, clusters and tendrils.
Spring will happen all too soon so for now I am happy to stay warm inside and enjoy the snow.