Flora Wonder Blog: Acer Part 2: The Hillier Manual of Trees and Shrubs, 9th Edition

In today's blog I'll discuss some Acer species listed in the 9^th edition of the very useful Manual.

Arboretum Hemelrijk

Now, many of you assume that I am a maple expert, right? Well, not so, or not very much. For example, ten years ago at the International Maple Society convention in Belgium we were touring the fantastic estate of the de Belder's called Hemelrijk, and one botanist asked me if I knew the specific identity of one towering Acer. I won't mention his name, but he didn't know me and perhaps assumed that I was an eminent botanist such as himself, as the international gatherings always attract the professorial types. I answered that I didn't have a clue, for basically I am a palmatum cultivarist. Another botanist overheard the question and soon there were four or five experts pondering the tree's identity. Various species were proposed, but no one seemed to be certain – and after all the leaves were high up in the air. I honestly thought it was an Acer rubrum, judging by the leaf debris below, but I've learned to keep my mouth shut. D. Justice from the University of British Columbia – one of the more likable of the botanists – waved it off with “Well, it's probably a hybrid anyway,” and then walked away. He makes a living off of maples, as do I, but I get paid only if my trees thrive and I can sell them, while he spends half of his day I suppose staring at dead herbarium samples.

Acer calcaratum

But no, I'm not an expert. One Acer species I encountered in the Hillier 9^th is Acer calcaratum. I have one 15-foot tree in a container in the greenhouse which is scrunched up against the top poly, so annually it will require heavy pruning. I love the rich reddish-purple new growth, but just with one look at the tree I can predict that it's not hardy outdoors for me. Hillier reveals that “A. calcaratum is from India (Sikkim) and the Himalaya. H2.” So I go back to the book's hardiness guide and H2 is a USDA zone 10 for me, so it's a wonder that it has survived at all in my unheated greenhouse. Seeking more information I turned to De Beaulieu's An Illustrated Guide to Maples but it's not listed at all...which suggests that Hillier is a splitter while De B is a lumper. Years ago I encountered similar-looking Acer species in Sikkim and in Himalayan foothills but was never certain about what I was seeing, but they too were blessed with delicious-looking new growth. Since my one tree came from the Nichols boys I went to their website mrmaple.com and was shocked to read that A. calcaratum is classified in the section palmata, and in fact the trees they sell are grafted onto Acer palmatum. How about that! I'll have to propagate a few and then I can sell my big tree to a southern California nursery.

Acer buergerianum 'Mino yatsubusa'

Hillier gives short shrift to the Acer buergerianum species, listing only 'Mino-yatsubusa' and 'Shirley Debacq', the latter which I have never seen. As I've mentioned before, Hillier is dash-happy-with-the-Japanese-names, presenting us with 'Mino-yatsubusa' as one of many examples. I don't think it's necessary or even valid, and you aren't dashed to death in De Beaulieu's An Illustrated Guide to Maples, Masayoshi Yano's Book for Maples or in the Vertrees/Gregory Japanese Maples, my three go-to reference books which I actually place ahead of the Hillier. Anyway 'Mino yatsubusa' is a most curious cultivar with unusual leaves where the middle lobe is long and tapering, and the top two lobes of the Trident are short and perpendicular to the middle lobe. It gives this rather dwarf bush a lacy appearance, but the real fun begins in autumn when the green foliage transforms into deep orange, red, purple and nearly black coloration...and all of these hues can be present at the same time. There are many wonderful cultivars of A. buergerianum – which all sell like hotcakes for me – so it makes me wonder if any of the others have reached England at all. Actually I don't recall seeing A. buergerianum cultivars at the Westonbirt Arboretum either, or maybe it's just that the late Director, Peter Gregory, led me down a different path...but, who knows, there could be scads of them now.

Acer campestre 'Carnival'

Surprisingly there are a far greater number of Acer campestre cultivars listed than with almost all other species except palmatum, but then the “Field maple” is native from Britain to western Asia. One such is 'Queen Elizabeth', a funny name since it was selected in America for “its vigor and upright habit.” Another interesting addition is 'Silver Celebration' which originated as a branch sport on A.c. 'Carnival'. Those sportations are actually common for me, where 'Carnival's' foliage can appear perfectly half-and-half – white and green – or be totally green which you should prune out...or totally white where nature can prune herself via sun burn.

Acer circinatum 'Sunglow'

Acer circinatum 'Sunny Sister'

Of all of the maples I have introduced – some would say too many – no cultivar was listed in the Hillier 8^th. Of all of my maples, of all species, the Hillier 9^th lists only Acer circinatums 'Sunglow' and its sister seedling 'Sunny Sister', but at least they spelled Buchholz korrect. So, no Acer macrophyllum 'Mocha Rose', no A. palmatums 'Fairy Hair', no Ghosts, no 'Japanese Princess'*, no A. shirasawanums 'Kawaii' or 'Sensu' etc. I'm not miffed that these were skipped, but they are all in Europe and certainly grown in far greater numbers than my two “Vine maples.” We don't propagate many, and sometimes we even skip a year because in our growing conditions they are both prone to powdery mildew. The few that we have are scattered in with the palmatums and could be in any of 50 greenhouses, so a spray program to control the mildew is not feasible. It would probably make more sense to not grow them at all.

*I find it baffling that the seed parent of 'Japanese Princess', 'Mikawa yatsubusa', is not included in Hillier's 106 A. palmatum cultivars.

Acer palmatum 'Shishigashira'

Of the 106 Acer palmatum cultivars listed in the 9^th, I grow about half of them, and though I have access to almost all, I perceive a poor market for the likes of 'Dissectum Flavescens', 'Hessei', 'Korean Gem', 'Rufescens' etc. I don't grow others because they tend to revert or suffer from mildew such as 'Beni komachi', 'Taylor' or 'Marlo'. Acer palmatum 'Shishigashira' is rendered 'Shishi-gashira' in the 8^th, but a typo occurs in the 9^th and it is 'Shish geshira' – two words but at least no dash. I prefer 'Shishigashira' – one word, and that's how you find it in the Vertrees/Gregory Japanese Maples.

Acer palmatum 'Red Emperor'

In the 9^th it is suggested that Acer palmatum 'Emperor I' is the correct listing with 'Red Emperor' as an inappropriate synonym. In the 8^th it was the opposite. I grew 'Red Emperor' before what we label as 'Emperor One' and I continue to keep them as separate cultivars, but I admit that they look about the same. 'Emperor I' is described as “similar to 'Bloodgood' but coming into leaf two weeks later, reducing the risk of spring frost damage...” Frankly I have not noticed that attribute in my nursery. My opinion whether or not 'Red Emperor' and 'Emperor One' are the same clone is: I don't know. A former customer – now bankrupt and out of business – asked me the question about 15 years ago. He grew 'Emperor One' and I 'Red Emperor' only, so we agreed to exchange 100 scions. A few years later he planted a row of one next to a row of the other in full sun. Then he reported to me when the trees were 6 or 7 years old that the color was the same but that the 'Red Emperors' were consistently taller, with the 'Emperor One' more wide. I never inspected his trial, which I now regret, but he insisted that they were not the same. For what it's worth, Vertrees/Gregory list only 'Emperor I' and say: “This outstanding cultivar of exceptional vigor was discovered and developed by Richard P. Wolff of Red Maple Nursery, Pennsylvania.” Then they conclude: “'Red Emperor' which also originates from Red Maple Nursery fits the above description and may be the same cultivar.” Sorry if the above comes across as excessive nitpicking, but that's how I have spent my career, by getting down to the skinny in all matters possible.

Acer oliverianum

Over 30 years ago I collected two Acer species, a seedling of both A. oliverianum and A. elegantulum from a Salem, Oregon collector with the fantastic name of Noble Bashor. You could graft both onto Acer palmatum rootstock and they were attractive trees but nobody would buy them. I suppose one problem was their perceived lack of hardiness, but then also my customers wanted “Japanese maples,” not two obscure “Chinese maples.” Indeed Hillier 9^th rates A. elegantulum as H4 (British) which translates to USDA zone 8b9a, about 10F. The A. oliverianum is H6, or H5 if you have subspecies formosanum, i.e. hardy to about 0F-10F. I finally sold off all propagules from these species and kept just the original tree of each, and they were planted in my First Road section, which was so-named because it is the first planting that visitors encounter when they come to Buchholz Nursery. I don't remember if it was a particularly cold winter or perhaps a late spring frost, but both developed a bad trunk where the bark had split. If they would have been planted off in the back of the nursery I might have allowed them to live and recover, but I executed them because I didn't want customers or the public to observe that I had damaged trees.

Acer oliverianum 'Hot Blonde'

I never made an effort to reacquire the A. oliverianum, except that a few years ago the Nichols Boys from North Carolina sent me a start of x 'Hot Blonde', which looks to be a chance hybrid of A. oliverianum and A. palmatum. I'm very excited about its prospects, and this past summer's grafts look very good. The Boys (at mrmaple.com) describe the beauty as a “gorgeous golden yellow upright Japanese maple with orange border in the spring. 'Hot Blonde' gets more and more yellow as the season goes on [and it] is a strong growing and vigorous tree, reaching 12-14 ft in 10 years.” After some more enthusiastic verbiage, they continue with the best part, that 'HB' “is one of the most heat tolerant Japanese maples we produce.” I highly recommend that you google Acer x 'Hot Blonde' and click onto mrmaple's Youtube presentation to learn more about it. The best part is we can see Amy Nichols for whom the tree was named, and she is absolutely a hot blonde – as in sizzling – and the only thing that makes you wonder is how teddy-bear Matt was able to land her as a wife, and he honestly admits to that himself.

Acer shirasawanum 'Moonrise'

I have produced thousands of grafts with the Acer shirasawanum species, beginning with the iconic A.s. 'Aureum' which was initially placed with Acer japonicum. In hindsight we must all be embarrassed to have gone along with the notion, because it became a very obvious taxonomic remedy once it was corrected. The Hillier 8^th lists three cultivars of A. shirasawanum: 'Aureum', 'Autumn Moon' and 'Jordan'...but the latter is a probable hybrid with palmatum and is not particularly suitable in horticulture due to its summer scorch susceptibility. The Hillier 9^th adds another cultivar, A.s. 'Moonrise', and it gets a glowing review: “Selected for its spectacular seasonal colour and resistance to leaf burn and disease...Introduced to the British Isles by Hillier Nurseries in 2016.” Well, concerning that last claim, I know that 'Moonrise' was in Europe well before 2016, and at least a dozen years ago I sent lots of scionwood to Junker Nurseries of Somerset, England, but now I'm too lazy to look into the archives to see if I sent 'Moonrise' as well. I find most A. shirasawanum cultivars to be more winter hardy than are the A. palmatums, even though the former are usually grafted on A. palmatum rootstock. It is usually more difficult to achieve a well-shaped canopy on the A. shirasawanum cultivars, including 'Moonrise'. We have learned that A. shirasawanum requires more discipline, more tough love, and we accomplish a balanced canopy by pruning, and never by staking. A six-year-old 'Moonrise' will not grow as tall as a six-year-old A.p. 'Red Emperor' for example, because the former requires more pruning.

Acer nipponicum at the SHHG

Acer nipponicum

I think I have visited the Sir Harold Hillier Arboretum three times, although I'll admit that my life's years and plant trips have blurred. On one visit I spotted a green tree in the distance with a distinctively stout appearance. I knew instantly that it was Acer nipponicum because I grow one at Flora Farm and I see it by the driveway every day. Hillier deems it “A very distinct species that remains rare in cultivation though a tree (now dead) at the SHHG fruited profusely and produced many self-set seedlings.” My specimen is of seedling origin too, as I know of no compatible rootstock. Years ago I quizzed the late maple author, Peter Gregory, about a possible rootstock and he suggested Acer pseudoplatanus “because it accepts so many.” I tried it and got 100%...failure. Brian Humphrey in The Bench Grafter's Handbook concurs that “A. pseudoplatanus and palmatum suggested; both have failed here.” A. nipponicum could possibly be the only Acer species that does not have a compatible rootstock, or at least I can't think of another.

Acer pectinatum 'Mozart'

Hillier's 9^th lists only one cultivar of Acer pectinatum, 'Mozart', which was “Raised from seed wild collected by Peter Vanlaerhoven.” If true, then it's ridiculous to ever have considered it a cultivar of Acer x conspicuum (A. davidii x A. pensylvanicum) because the one Asian species and the other American do not meet in the wild. Of course this old American readily hybridized with an Asian species and the resulting offspring turned out pretty good. Acer pectinatum varies greatly in the wild with at least four subspecies originating in Yunnan, China, northern Myanmar, Bhutan, eastern Nepal and the southern Himalaya. All of that matters due to the possible hardiness of 'Mozart', but I don't know where it was “collected in the wild.”

I'm happy to have received the revised and updated 9^th edition and it is certainly packed with a wealth of information. This blog, as with last week's Conifers, Part 1 is not intended as a review in the traditional sense, it is rather an autobiography of my experience with the trees contained therein. My copy is already dog-eared and a little dirty from use, having become a new friend that I take advantage of. You can be sure that I will pounce to acquire the 10^th edition whenever that will be.

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Friday, September 25, 2020

Acer Part 2: The Hillier Manual of Trees and Shrubs, 9th Edition

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