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Plant Focus

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Dwarf cultivars can be ideal for a small garden. Here are three "mini oaks". 

Hybrid Oaks Under Evaluation

For nearly 15 years, Nina Bassuk and her grad students at the Cornell Urban Horticulture Institute (UHI) have been developing hybrid oaks for exceptional tolerance of urban conditions (drought, alkaline soil, etc.). About 250 hybrid oaks of 2–3 inch caliper have now been distributed to some 40 communities in New York State where they are being planted out so they can be evaluated over time.  

macrocarpa x turbinella
Quercus macrocarpa × turbinella 

Between 2004 and 2006 Nina received pollen from about 40 oak species in the White Oak group (section Quercus) from all around the country. She and her students used oaks from the Cornell Botanic Gardens and Arboretum as mother plants to create new hybrids for urban use. “The idea was to create cold-hardy oaks that were tolerant of alkaline soils, drought, diseases such as powdery mildew, and that had good form,” she says. “We also wanted to propagate them clonally, on their own roots, to avoid graft incompatibility which is a problem for oaks in general.”

Hybrid oaks in UHI research plots.
Hybrid oaks in UHI research plots.

The maternal species were located on the Cornell campus in Ithaca, New York and include several native and purported hybrid white oaks: Quercus bicolor, Q. gambelii × macrocarpa, Q. macrocarpa, Q. macrocarpa ‘Ashworth’, Q. montanaQ. muehlenbergii, and Q. ×warei ‘Long’ (Regal Prince®). Some of the paternal species include Q. virginiana, Q. lyrata,  Q. robur, Q. fusiformis, and Q. polymorpha. Over 350 unique hybrid genotypes were developed and over the years these hybrids have been evaluated for tolerance to cold temperatures, drought, and high pH soils. 

Fall color
Quercus macrocarpa × gambelii × lyrata growing experimentally on the Cornell campus

At the same time, Nina and her team have researched asexual propagation techniques that would allow for desirable characteristics to be passed on to large numbers of new trees for introduction to the nursery trade. Their approaches have included the use of modified stool beds and tissue culture.

tissue culture
Oak shoots multiplying in tissue culture

Trees propagated from the oak hybrids have been evaluated in UHI research plots and many have also been planted out on the Cornell University campus in Ithaca, at the Geneva Experiment Station, at Schichtel’s Nursery in Springville NY, and at Green-Wood Cemetery in Brooklyn

The work has taken over 25 years and has allowed researchers to improve their understanding of these hybrid oaks. “We are confident,” says Nina, “that we may have some superior urban-tolerant oaks to introduce in the near future.”

warren
Quercus ×warei × ​×​​​​​​comptoniae growing experimentally on Cornell campus