Acer palmatum

Fall 2018 in Georgia was superb for exacting picture-perfect, true-to-marketing, retina-saturating autumn colors from Acer palmatum and cultivars. One might ask, who needs a cultivar when run-of-the-mill seedlings radiate brilliant yellow, orange, red, scarlet, and purple, often a mixed mottle on the same tree?

I doubt any one knows the exact number of extant cultivars, however, 484 are listed as commercially available in the RHS Plant Finder (2017). Remarkable variation exists within the genome of the species as evidenced by dwarf shrub types, weeping, columnar, and small to medium trees. Stems and trunks variously colored and textured. Foliage may be lobed, filigree/dissected, and thread-like in green, yellow, variegated combinations, red, maroon and purple. Foliage is frost/freeze tolerant into the low- to mid-20s; the colder temperatures fostering the great fall colors. Fall color develops equally well in sun and shade environments, making it a useful understory plant. In its native Japan and Korea, it grows in the understory. In the Dirr and Coach Vince Dooley gardens, seedlings and cultivars are planted under water, willow, and white oaks, tuliptrees, and pines, displaying cultural tenacity not consistently credited to the species. Once established, the species displays reasonable drought tolerance, pH adaptability, and longevity. Avoid wet soils as trees require good drainage. Antiquarian trees (over 100 years old) are extant in landscapes from Maine to Georgia. In Newport, R.I., on the estates along Bellevue Avenue, trees that are 30 to 40 feet high, 50 feet wide, with 3- to 4-foot diameter trunks are in excellent condition. Zone 5 to 9 is the reasonable assessment of adaptability, especially with proper cultivar selection. A friend from Marinette, Wis., sent grafting wood of a pretty seedling in his garden that survived -37°F, so there is hope for Zone 4 (3) gardens. New hybrids with the cold hardy A. pseudosieboldianum have been recently introduced by Iseli Nursery and others.

Acer obsession

Once hooked on the lure/diversity within Acer palmatum, collecting becomes an obsession, with the next unique cultivar only $129.99 out of pocket. Coach Dooley developed a love for Japanese maples long before me, although I am now trying to catch up. Coach has 125 cultivars and 50 seedlings, spiced with Acer japonicum,A. shisarawanum, and a single, truly magnificent A. pseudosieboldianum, the latter I did not believe would be so successful in the Zone 8 heat. Coach bought his wife, Barbara, an Acer palmatum for an anniversary gift. As the story unfolds, coach said she kept looking for jewelry on the branches and all she discovered were leaves. We walked the garden 11-17-18 and again on 11-21-18, colors at their peak, with a few still green like ‘Katsura’ and ‘Mikawa-yatsubusa’. The majority of the so-termed red leaf cultivars were brilliant red and/or purple.

Japanese maples are frequently described as slow-growing small trees, in the 20-foot range. A Chinese proverb opines, “The best time to plant a tree was 20 years ago; the next best time is today.” Coach’s love affair with Acer palmatum started in the late ‘90s. In fact, when I first visited his garden in 1995-96, I do not remember a single A. palmatum. The early additions like ‘Oshio-beni’, ‘Trompenburg’, ‘Glowing Embers’, ‘Katsura’, and many seedlings are now over 20 feet high. ‘Glowing Embers’, a seedling selection from the University of Georgia Botanical Garden, is now 30 feet high. Coach is still planting and added several more in 2018. He has a menagerie of maples in containers on the patio, carefully observing their performance, before moving them to the garden.

I asked Coach to develop a list of his top performers and/or those with personal attachments (see sidebar). My list, based on consistent aesthetics and performance in the nine-year-old Dirr garden, is also included. There are currently ~25 cultivars and ~15 seedlings in the Dirr garden.

I gave Coach a stray, dissected, green leaf seedling that, at the time, showed little promise. Fifteen years later it is one of the more unique A. palmatum in his garden, christened/labeled ‘Dirr Throwaway’. Serpentine habit, green stems like Firmiana simplex, and delicate fern-patterned green leaves which turn glowing yellow-gold-orange in autumn, enticed me to graft several. Does the world need another Japanese maple? Certainly not. But even a benchwarmer surprises and occasionally scores a touchdown. Mark Krautmann of Heritage Seedlings in Salem, Ore., suggested the name ‘Dooley’s Quarterback Keeper’.

In the southeast, persistent red leaf foliage color is the missing ingredient in all the red leaf cultivars. All red leaf types are green or nearly so by July in Zone 8. In New England, the upper Midwest, and the Pacific Northwest, the red color persists into fall. A study at North Carolina State University showed “redness” of ‘Bloodgood’ foliage grown at 57°F and 64°F night temperatures was two to seven tones darker than foliage at 72°F and 79°F. I have asked everyone who knows/grows the red leaf types for those with the most persistent coloration. In the southeast, ‘Hefner’s Red’ (‘Hefner’s Red Select’) and ‘Emperor 1’ consistently surface. To these, add ‘Nuresagi’, which has been the best for red leaf retention in the Dirr garden. ‘Fireglow’ and ‘Twombley’s Red Sentinel’ are also mentioned for holding red leaf color. The fall color is always brilliant red on ‘Emperor 1’. ‘Fireglow’ and ‘Hefner’s Red Select’ are of an intermediate size for red leaf uprights, 12-15 feet high at maturity.

Zone 8 considerations

The challenge for A. palmatum enthusiasts/breeders is to develop a cultivar with season-long red foliage under high day/night temperature conditions. A red leaf tree type like the dissected green leaf ‘Seiryu’ or weeping ‘Ryusen’ are worthy objectives. Both are well adapted to the heat of Zone 8. ‘Ryusen’ from seed produces upright and weeping specimens. All seedlings to date have green foliage. Japanese maples will “seed in” and are often found around older trees where the ground is undisturbed. I have collected many as has Coach Dooley from such habitats, with the thought that nature will provide the persistent red foliage of my dreams. Unfortunately, I am still dreaming.

There is a Japanese maple for every garden situation offering variation in habit, size, foliage, stem/bark coloration, and adaptability. Hale and Hines Nursery, a wholesale pot-in-pot grower in McMinnville, Ten., lists 40 A. palmatum cultivars in the 2017-2018 catalog. There are many specialist growers who offer a spectrum not often available from local retailers. The specialists often discover new forms and introduce them in local and regional markets. David Freed, owner of Garden Design Nursery in Madison County, Ga., introduced ‘Twinkles’ and Radiant, the former a more compact, finely branched, coral red stemmed type, 8-10 feet high; the latter strongly upright-vase-shaped, to 15 feet high with variegated green-white-pink-rose spotted and marble-cake patterned leaves and green-white-yellow streaked bark. David grafts all the cultivars in-house and monitors their adaptability for the Georgia climate. Coach and I visited on Dec. 7, 2018 and purchased six new cultivars for our gardens.

For more than 40 years, horticulturist, breeder, and author Michael A. Dirr has impacted the green industry through research, teaching, books, and plant introductions. Coach Vince Dooley is a former University of Georgia football coach and athletic director. He’s since become a garden enthusiast and plant collector who can ID plants and use the correct botanical names with the best of them.