Impact of Chilling on Ginkgo Bud Break

Ginkgo biloba is an ornamental tree of prominence and value in the green industry. Often referred to as a 'living fossil', ginkgo grows well in USDA Hardiness Zones 3 through 9 , reaching a mature height up to 80' and width of 40'. With a slow to medium growth habit, trees are often pyramidal when young and become wide spreading when older. Ginkgo is insect and disease resistant making it an excellent choice for a city tree with over 40 cultivars available. Though much work has been done with fruit species with respect to dormancy and chilling requirements, no work has been reported regarding chilling requirements with G. biloba. Chilling units are generally based on the number of hours accumulated below 45°F. The objectives of this study were to determine chilling and dormancy requirements for this species in order to increase production efficiency.

Increasing the number of chill hours led to a decreased amount of time required inside the greenhouse to reach 50% foliar bud break. In most cases, increased chilling produced a higher percent foliar bud break. Bud break percent increased with the increase of approximately 1000 chill hours. Trees that were in the cooler for an extended period of time were able to reach the point of 50% foliar bud break with less accumulated time inside the greenhouse. This was evident with trees receiving 800 - 1100 chill hours when compared to all other treatments.

Increased chilling led to a decreased heat requirement to initiate bud break. For growers producing G. biloba liners in greenhouses, adjusting environmental conditions to allow chilling can accelerate and lead to more efficient production for container grown G. biloba. As for field or outdoor production, while it is possible to produce G. biloba in USDA Hardiness Zones 3 through 9, our work indicates trees may reach a profitable size more rapidly in regions that accumulate greater than 800 hours of chilling.

(from 2002 student research paper presented at SNA by Jeffrey C. Wilson, Jeff L. Sibley, James E. Altland, Ken M. Tilt, and Wheeler G. Foshee, III, Department of Horticulture, Auburn University.)

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