Quercus canbyi Trel.

Quercus canbyi can be evergreen – or not. It straddles the edges of deciduousness, and in cultivation its foliar phenology acts as a litmus test of sorts for the coldness of a climate or the severity of a winter. The species is often described as semi-evergreen, with foliage that has proved persistent in warmer climates and tardily deciduous in colder ones.

It is an attractive medium-sized tree, usually reaching 10 to 15 m tall, though some sources indicate specimens of up to 25 m have been found in habitat. It adopts a pyramidal form while young, spreading out into a broader canopy after a few years and taking on an open, irregular shape at maturity. It grows fast and has attractive dark foliage that veers towards red at least once in the year: on emergence in spring and sometimes again in late fall or winter. Meléndrez (2000) raves about growth of 1.2 to 1.5 m a year at Las Lunas, New Mexico, (1500 m, Zone 7a) with a last flush in September that is still able to harden up enough to withstand a hard frost in October; he reports it is semi-evergreen in that location, turning maroon in winter and keeping this color for months. His specimen was apparently sourced at almost 2500 m, which is slightly higher than the upper limit mentioned by Romero Rangel (2006).

In Houston (Zone 9) it is evergreen and in San Antonio Botanical Garden (Zone 8) mostly so (Garrett 2008; Garrett 2004); at the SFA Gardens of Stephen F. Austin State University in Nacogdoches, some 250 km north of Houston and deep into Zone 8, a tree sourced by Lynn Lowrey from Nuevo León, Mexico, and referred to by him as the ‘evergreen form,’ keeps its leaves in most winters and has never suffered limb die back or bud damage, though temperatures below –12°C have removed its foliage (Creech 2016). In northern California it displays winter foliar colouration from Christmas to Valentine’s Day, which, according to Dave Muffly (2023), ‘can be quite spectacular.’

It is hardy beyond what would be suggested by its natural range and especially so in the case of specimens of high elevation origin. It has done well at JC Raulston Arboretum in Raleigh, North Carolina (Zone 7b), reaching 12 m in some twenty years (JC Raulston Arboretum 2023), with a growth rate that at times reaches 1.8 m a year (Raulston, Fairey & Schoenfeld 1995). At Aiken, South Carolina, (Zone 8a) it suffered damage in an unusually severe frost that plunged to –7°C and came late in the season, when plants had broken dormancy and sprouted catkins and new growth (Russell 2017).

In France it has been praised for its rapid growth at Arboretum de la Bergerette, where it has proved one of the most rapid-growing of the Mexican oaks Shaun Haddock has planted: a specimen planted in November 2008 reached over 4 m in early 2012. The species is drought tolerant, but another specimen at la Bergerette was cut back by the extreme drought in 2003 and so may not be appropriate for extremely dry areas (Haddock 2012). At Kruchten, Luxembourg, it is fully deciduous in normal winters, losing its leaves late in December when temperatures dip to –15°C, though in very mild winters it may retain a portion of its foliage (E. Jablonski, pers. comm. 2023).

Though The Hillier Manual (Edwards & Marshall 2019) marks it as a plant that will not tolerate alkaline or chalky conditions, several authors indicate it grows well on alkaline soils of limestone origin (e.g. Creech 2016; Melendrez 2000).

It seems Quercus canbyi was first introduced to cultivation in the US by famed Texas plantsman Lynn Lowrey, who collected it in Mexico between Saltillo (Coahuila) and Monterrey (Nuevo León) sometime in the 1970s (Huber 2004; Pickens 1999). It has proved very successful in gardens in Houston and other locations in Texas. According to Fairey & Schoenfeld (1994), Q. canbyi adapts to almost any soil and once established is extremely drought tolerant and ‘tough’, citing as evidence the fact that it grows in the generally poor soil and scorching heat of Texas cities. It has also proved resistant to a fungus causing oak decline and destroying colonies of large Q. fusiformis trees in the Hill Country of Texas.

Introduction to the UK followed soon after: Sir Harold Hillier collected it in Mexico in 1979, and a tree of that source (Hillier 619) survives at Sir Harold Hillier Gardens, reaching 17 m × 57 cm dbh in 2017. It is also found in several collections in England and Wales: at Chevithorne Barton, Devon, a tree planted in 2003 reached 7 m × 13 cm in 2017 and has been known to retain shiny green leaves as late as January (Heathcoat Amory 2009; The Tree Register 2023). However, the champion in cultivation may be a specimen in Hackfalls Arboretum in New Zealand, grown from seed collected by Bob Berry on Cerro de Chipinque, Monterrey, in 1989. The largest of four trees of this source had a dbh of 61 cm in 2020, and a height well in excess of 20 m (Berry 2016; Hackfalls Arboretum 2023).

Several minor variants of this species have been named, differing in the size of the leaf and the number of teeth, but they are usually regarded as part of the normal variation of the species (Coombes 2017). In cultivation it appears to hybridise readily with other red oaks, and Creech (2016) and Berry (2016) report obvious hybrids in the seedlings from cultivated trees; the hybrids are nevertheless easy to segregate from those that appear true to form. Putative hybrids have been recorded with Q. sartorii and Q. rysophylla in oak collections (Hackfalls Arboretum 2020, B. Chassé, pers. comm. 2022); at Sir Harold Hillier Gardens, plants raised from seed collected from a Q. rysophylla appeared to have hybridised with a nearby Q. canbyi (Coombes 1998).

When he named the species, Trelease (1924) dedicated it ‘to the memory of my late friend, Mr. W.M. Canby, in whose company I had the pleasure of collecting in its habitat.’ William Marriott Canby (1831–1904) was a US banker, philanthropist, and botanist.