How Long Can Grapevines Stay Dormant?

What is Dormancy?

• The dormancy of a grapevine is a state where the plant goes into rest. The plant hardens in order to become resistant to the winter conditions and goes into an energy conservation mode. This means the plant's energy goes to keeping itself alive rather than producing buds, growth or fruit. Right before a grapevine goes dormant it draws extra nutrients from the soil to build up the reserves it needs to get it through the winter.

Hours of Chilling

• Grape growing experts talk about the dormancy periods of grapes in terms of the number of hours the grapes get below a certain temperature. Getting the right amount of exposure at this temperature is critical for grapes that are strong and healthy the following year. The hours count when temperatures get below 45 degrees. Grapes need anywhere between 250 and 800 hours of winter below that temperature. Grapes stay dormant longer than that, but receiving that time at a colder temperature is critical for dormancy.

Northern Grapes

• To understand how long grapes can truly stay dormant, just look at climates with the longest winters and where grapes are successfully grown. Many Northern varieties of grapes stay dormant from between five to seven months. Other grape vines may be able to stay dormant this long, but may have too long of a growing season to produce quality fruit before the frost hits in the fall. The key is choosing the right variety of grape for your growing area.

Temperature

• The length of dormancy isn't always the most important thing. Grapes stay dormant as long as necessary, depending on the variety. However, the temperature of the air or soil during those dormant periods is important. For example, while grapes can survive temperatures even below zero, they can't survive rapid changes in temperature. Sometimes grape vines are covered or buried to help reduce these effects.