Conifer Cousins: Ginkgo biloba
Take a deep dive into a biological cousin of the conifers: the Maidenhair Tree.
My introduction to Ginkgo biloba was years ago, as a third year biology student at Vassar College in Poughkeepsie, New York, when my path between fall semester classes took me past a large tree with foul-smelling fruit. I was puzzled, because I had passed the tree for two years and never so much as wrinkled my nose. A member of the botany faculty enlightened me. It was a Ginkgo.
Ginkgo are dioecious and wind-pollinated; the tree in question was female, and the only male specimen on campus was far enough away that the wind conditions had to be just right at pollination time, which made success sporadic. Little did I know that that was the last time that I would ask a question about a Ginkgo and receive an unequivocal, short, factual, useful answer!
I embarked on the quest to make order of the world of dwarf Ginkgo cultivars only to learn that it is a world rife with confusion, lack of documentation, little long-term growing experience and enormous reliance on second-or even third-hand observations and interpretations. The usual frenzy on the part of collectors to obtain the latest, rarest, most unusual cultivars has added to the obfuscation, as it provides motivation to keep nomenclature fuzzy and the number of different offerings high. These conditions plague other genera, as collectors of dwarf conifers are only too well aware, but the world of dwarf Ginkgo has some peculiar characteristics which exacerbate the situation.
The History of Ginkgo
Ginkgo are not strictly conifers, and, at this writing, have been classified into their own division, Ginkgophyta, with a single class, order, family, genus and species, of which Ginkgo biloba is the only extant representative. The Ginkgo fossil record dates back some 200 million years. Native to China, they are believed to be extinct in the wild, as today’s populations now appear to have been cultivated. Ginkgo are, however, gymnosperms, and so are more logically lumped with conifers than not, and the American Conifer Society includes them under its umbrella. Ginkgo biloba ‘Mariken’ was even chosen as the American Conifer Society's Collectors Conifer of the Year in 2007.
Even those who have not grown Ginkgo almost certainly recognize them, as they are used ubiquitously as street trees, due to their extensive range, high tolerance of air pollution and their resiliency to wind and snow. In addition, because they are stoic, long-lived, and generally slow growing, they require little maintenance. Their durability is exemplified by the six Ginkgo trees which survived the atomic bomb blast in Hiroshima, a trauma not likely to be approximated in anyone’s garden, black thumbs notwithstanding! The lovely, iconic Ginkgo leaf is a familiar shape in art, craft and jewelry. Ginkgo have long been a favorite choice for bonsai.
Dwarf cultivars began appearing in the trade in the mid-1980s and there are now somewhere around 30 available in the U.S. As noted, Ginkgo is a monotypic genus. Thus, all cultivars come from one species, limiting the range of variation. Not all are reliably named or documented and many are so new that not much is known about growth rates, mature size and form, or even sex, as Ginkgo generally do not flower or fruit for 20-25 years. Whereas the species generally has a large, irregularly shaped crown, dwarfs come in a variety of shapes and sizes. Some are low and branching, others vase-shaped, columnar or pyramidal; some have different shaped or sized leaves. and one even has interesting bark formations.
Cultivation and Propagation
The cultural requirements of Ginkgo cultivars are similar to those of the species, and they generally all share the trait of buttery, golden autumnal color. The vast majority of cultivars originate as witch’s brooms, which Ginkgo produce with reasonable frequency. Two notable exceptions are ‘Gnome’, which originated as a chance seedling at Iaian Hiscock’s Commercial Nursery in Tennessee, and ‘Ross Moore’, which Ross Moore, of Moore’s Natives in North Carolina, found growing in a client’s garden.
The majority of named cultivars (except ‘Green Pagoda’, which, per its catalogue, Stanley & Sons grows from cuttings) are propagated by budding or grafting, with the scion wood of the desired plant grafted onto seedling rootstock of Ginkgo biloba. Lucille Whitman, of Whitman Farms in Salem, Oregon explains: “Much of the scion wood for dwarf Ginkgo cultivars is in short supply, due to the slow growth rate of the plants, their small stature, and their relatively short time in commercial propagation.
However, the good news is that if you can obtain the scion wood, grafting is easy and has a high success rate.” Due to this shortage of scion wood, many of the newest and sexiest cultivars are perpetually sold out and difficult to lay one’s hands on. Crispin Silva, of Crispin’s Creations Nursery in Molalla, Oregon, echoes Lucille’s frustrations about the scarcity of scion wood; he described building up a stock of scion wood as his biggest challenge in propagating Ginkgo cultivars.
Confusion in the World of Ginkgo
It quickly becomes apparent after talking with growers that there have been many new introductions over the last decade or so and very little documentation as to their specific growth patterns, growth rate, stability and variability. Add to that the scarcity of scion wood and the general slow growth rate of the genus, and you have a situation rife with approximation, hyperbole, and misrepresentation, even if much of it is unintentional.
A quick search of Ginkgo cultivars on the GardenWeb Forums, for example, produces pages of questions with incomplete, conflicting or unsatisfactory answers. Many of the cultivars have uncertain antecedents: for example it is not clear if ‘Chris’s Dwarf’ and ‘Munchkin’ are synonyms or not - two distinctly different forms have been observed. A similar situation arises with ‘Chase Manhattan’ and ‘Bon’s Dwarf’, with some claiming that they are the same plant, others that they are distinct and different.
There is also confusion surrounding the four or five offerings which originated at Spring Grove Arboretum in Ohio. One cultivar is named Spring Grove™, which is the trademarked name for a cultivar called ‘Grovbil’ (presumably a purposely un-euphonious shortened combination of Grove and biloba), which was originally termed Spring Grove #9. Thus, at one time or another, three different names have been applied to the same cultivar. ‘Grovbil’ only appears as a secondary name in the listing in the Spring Grove Arboretum catalogue - the plant is universally known as Spring Grove.
Another cultivar was originally named Spring Grove #86, but renamed 'Jehosephat'; another is called ‘Spring Grove Sport’ and another was recently registered as ‘Queen City’, which may or may not be the same as #22, which is referred to on several sites. ‘Queen City’, although a legitimate cultivar, is so new that an internet search comes up completely dry. There may be yet another not in commercial distribution.
Richard Larson, Nursery Manager of the Dawes Arboretum in Newark, Ohio and the North American Registrar for all conifer genera (once again, Ginkgo are included) expresses his frustration with the situation: “Registration is relatively easy and it’s free, but a lot of people don’t want to register plants, so we have Ginkgo coming out [which] were never registered. That means that there is a lot of anecdotal evidence about a number of dwarf cultivars, but no recorded information.”
He also notes that like certain other conifer genera, such as Taxus, Ginkgo are strongly plagiotropic, so that scion wood taken from different parts of the stock plant produces different growth patterns in the grafted product. This makes for differing growth patterns within one cultivar, raising questions about whether the plants are truly of the same name. Finally, due to lack of funds, the annual ‘checklist’, or perusal of the literature of a particular genus, which is supposed to be done on Ginkgo is not being completed, so that there is no current list of legitimately registered Ginkgo cultivars available, to serve as a guide as to which cultivars are “legit” and which might not be.
The Ginkgo's Battle of the Sexes
Because oddities are sought after by collectors (and consequently valuable), any indication of a different growth pattern is emphasized, although it should be noted that Ginkgo, their cultivar names or descriptions notwithstanding, do not display variable forms to the degree observed in other genera. When asked about weeping forms, for example, Richard notes: “No Ginkgo is going to weep like a cherry.” Similarly, Gary Handy, of Handy Nursery, when describing ‘Robbie’s Twist’, says that despite the fact that it is often described as “contorted”, “It is not a true contorted, like say a filbert or a corkscrew willow.” So, for those of you seeking the unusual, temper your expectations and remember that the dwarf Ginkgo are going to display more subtle modifications of the species habit than you might hope to find.
Another peculiarity of Ginkgo cultivars is that most people prefer male plants, due to the malodorous qualities of Ginkgo fruit, which is botanically not a fruit, but rather the fleshy outer coating of the seed. While some female offerings exist, selected and grown for those who appreciate the taste of the hard inner seed, the vast majority of named cultivars are male, or thought to be male. So, now we are down to one sex of one species, from which to produce cultivars!
In fact, because so much Ginkgo propagation is restricted to cloning male plants, there is thought to be some threat to the biodiversity of the genus. It seems odd that the sex of the plant should matter much with a dwarf, especially one that can take 20 years to bear, where the ‘fruit’ would be far fewer than on an enormous species tree, but “male” has become an important adjective in Ginkgo marketing. Therefore, male plants are promoted.
Muddling through Ginkgo Marketing Talk
Clarity is made more elusive still by the fact that many retailers include boilerplate language in their write ups, such as “flowers and fruit are not ornamentally significant”, which implies that the cultivar in question has fruit and is thus a female, when in fact it is a male cultivar. A quick Google search for any number of cultivars reveals exactly the same language on different retail - and in some cases wholesale - websites, indicating that many vendors simply copy (with or without permission) the descriptions supplied by others. One retailer, when contacted about the accuracy of the descriptions of his Ginkgo offerings admitted that they were written by a third party and he had no idea if they were correct or not!
In addition, most retailers, even the more knowledgeable, specialty nurseries, have a very short (and often very narrow) experience with dwarf Ginkgo cultivars, and so must rely on others to provide specifics about growth rates, habit and other particulars. When someone cannot speak from personal experience, there is far more opportunity for descriptions to get mangled. We have been playing the Ginkgo version of “telephone”, the old game where a phrase or word is repeated down a line of people until what the last person hears bears little resemblance to what the first person said.
Thus, a particular cultivar is described by different vendors as “columnar”, “irregularly branching” and “arching and curving” - surely contradictory! Given the difficulties, what’s a collector to do? Stay tuned for the next issue of the Conifer Quarterly, where we’ll share the results of our interviews with growers, retailers, arboretum professionals, and plantaholics with a list for those who want the most reliable selections…and further, choices for those who want to push the envelope!
Thumbnail photograph by Jerry Wang. Catalogue photographs by Harold Greer.
This article was originally published in the Winter 2013 issue of Conifer Quarterly. Join the American Conifer Society to access our extensive library of conifer-related articles and connect to a nationwide group of plant lovers! Become a member for only $40 a year and get discounts with our growing list of participating nurseries in our Nursery Discount Program.
Thank you for this excellent article....Conifer Cousins: Ginkgo biloba. I am a little confused regarding the use of the term “plageotropic” (plagiotropic?). The useage in the text does not seem to fit the definition. Can you please elucidate?
First, thanks for catching the typo! I believe what Rich meant here is that the lateral branches of Ginkgo are hard-programmed to be lateral. So by grafting using scions from the laterals, you are likely going to get growth that is not orthotropic, or at least not strongly so. Does that make sense?