Grape-leaf Fullmoon Maple Brings Brilliant Fall Color to the Seattle Japanese Garden
by corinne kennedy
Two impressive specimens of Acer japonicum ‘Vitifolium’, planted at the south end of the Garden, on both sides of the main path. This photo was taken from the Garden entrance, looking northward. (photo: Aleks Monk)
The Seattle Japanese Garden is home to more than 100 maple trees—including a total of about 35 maple species (trees that grow wild in nature) and their cultivars (the cultivated varieties, grown from grafted cuttings, that are bred from wild-growing trees).
Most maple species (in the genus Acer) are native to temperate regions in the Northern Hemisphere, including the Pacific Northwest. Two of these species—native to Japan and prominent elements within the Seattle Japanese Garden—are among my favorite deciduous trees. These two are Acer palmatum, commonly known as Japanese maple, and Acer japonicum, known as fullmoon maple.
Confusingly, the literal translation of Acer japonicum is “Japanese maple,” which is the common name of the other maple species, Acer palmatum. However, the latter and its hundreds of cultivars are better-known and more often planted here and abroad, so perhaps it merits that common name.
Cultivars of both species and several additional maple species are celebrated in the Garden’s Maple Festival, held every year in October. A little-known fact is that even when different maple species grow together in the wild, they do not hybridize with each other. So even within our Garden, these two species have not produced “interspecific” hybrids.
The Fullmoon Maple Species
Acer japonicum is a medium-sized deciduous tree native to the mountain forests of Japan, on the islands of Honshu and Hokkaido. This species and most of its cultivars are sturdy, strong-growing, adaptable trees known for their brilliant fall colors. Their leaves, sharply and irregularly toothed, usually consist of 9-11 lobes with a rounded outline that resembles the full moon—hence its common name, fullmoon maple.
Growing wild in large areas of Japan’s coldest island, Hokkaido, Acer japonicum is relatively cold hardy, to at least USDA Zone 6 (minimum temperature -10 degrees Fahrenheit). It grows well in sun or shade, so long as the sun is not too intense and the soil remains moist. In Japan it’s traditionally been trained as bonsai or planted as a garden focal point, as a street tree, or in a mass planting.
Here’s a taxonomic detail that may be of interest to plant geeks: In 1984, several Acer japonicum cultivars, including ‘Aureum’, were reassigned to a related species, Acer shirasawanum.
Illustration of Acer japonicum and its parts (image by John David Tobe; Creative Commons, Attribution-NonCommercial 4.0)
In Japan this species is known as hauchiwa-kaede, a reference to the toothed leaves that resemble a feather fan. Hauchiwa combines ha (leaf) and uchiwa (fan). The word kaede means maple, maple leaf, or maple tree.
Its alternative Japanese common name, meigetsu-kaede, is more consistent with the English term, fullmoon maple. It combines the word for maple with meigetsu, a reference to the bright or full moon.
Horticultural authorities note that cultivars of Acer japonicum are considered difficult to identify because they so closely resemble seedlings of the species. The value of maple cultivars, however, is that because they’re grown from grafted cuttings, not seeds, they have predictable characteristics—including the highly valued trait “dependable fall color.”
Grape-leaf Fullmoon Maple
Two specimens of Acer japonicum ‘Vitifolium’ are located at the south end of the Garden, on both sides of the main path. ‘Vitifolium’ is larger growing than most of the other fullmoon cultivars. Young trees have a slender upright habit, but become round-topped and wider with age. Their height at ten years is about 12-15 feet, and at maturity (about 20-25 years) about 25 feet. Growth then continues, though at a slower rate. The older of our Garden’s two trees, at more than 60 years of age, is approximately 40 feet tall.
Delicate purple-red flowers, held in large drooping clusters (corymbs), appear in spring before the leaves. Fruits are nutlike samaras (a simple dry fruit with wings and usually a single seed). About one inch long, they ripen in late summer or early fall, spinning through the air as they fall from the tree. People often call them whirlybirds or helicopter seeds.
The delicate spring flower clusters of ‘Vitifolium’ fullmoon maple. (photo: Aleks Monk)
The bark of ‘Vitifolium’ is gray-brown and smooth, and its leaves are thick-textured, coarsely-toothed, and about 5-6 inches wide. They have long, stiff leaf stalks (petioles) and the characteristic rounded outline of the species. However, their 9-11 lobes are somewhat more deeply divided, slightly over halfway to the base. In spring, the large leaves emerge bright green with tinges of bronze, then mature by summer to a dark green. They resemble the leaves of grapes, which are in the genus Vitis—hence the name ‘Vitifolium’, which means “grape-leafed.”
This cultivar is renowned for its dependable fall colors—brilliant scarlet, orange, crimson and yellow—even under somewhat shady conditions. It closely resembles the species, and according to German woody plant authority Gerd Krüssmann (1910-1980), many trees then labeled ‘Vitifolium’ were in fact the species plant.
Crimson and gold fall color developing on the leaves of Acer japonicum ‘Vitifolium’ in the Seattle Japanese Garden. (photo: Aleks Monk)
‘Vitifolium’ grows best in light to open shade, or in some locations full sun. In areas with hot afternoon sun and/or reflected heat, it requires some shade. It prefers rich, well-drained soil, but is somewhat adaptable to less than ideal soil conditions, so long as drainage is adequate. Because Japan has a wet-summer climate, regular watering is needed in our region’s dry summers. Inadequate irrigation will result in leaf burning that spreads inward from the tips.
Pruning fullmoon and Japanese maples requires horticultural knowledge as well as aesthetic judgment. Inexperienced pruners can easily destroy the shape and value of their tree. Gardeners interested in developing pruning skills should look for locally available classes. Alternatively, the non-profit Plant Amnesty offers free referrals both to experienced pruners and certified arborists.
Where Did the Garden’s Grape-leaf Fullmoon Maples Come From?
The Seattle Japanese Garden’s two trees were received from different sources. Plant material for the tree on the west side of the path (Area Z) was received by the Washington Park Arboretum (WPA) in 1963 from the U.S. National Arboretum. However, the plant material consisted of cuttings suitable for grafting (scions), not living plants. In the WPA nursery, the scions were grafted onto rootstocks and then grown on for several years. Our Garden’s tree was planted in 1969.
The other tree, on the east side of the path (Area C), was received in 1964 as a very small tree, only eight inches tall, from Belgium’s Arboretum Kalmthout. It was also grown on in the WPA nursery, but unfortunately no planting date was recorded. The WPA’s Accession Card simply contains a hand-written note: “on east side of dry creek near south entrance to Japanese Garden.”
Accession Cards for both trees include the same brief 1983 comment (“plant thriving”) by WPA Director Emeritus Brian O. Mulligan. He apparently did a survey of the Seattle Japanese Garden that year, making Accession Card notations about the condition of many of its woody plants.
Some Brief Advice
Acer japonicum and its cultivars are understory trees. They’re well adapted to our region’s temperate climate, but with our planet’s changing climate and our own region’s dry summers, they will struggle without sufficient irrigation and at least some afternoon shade. Planted in optimal soil conditions, and at the edge of a woodland or where taller trees provide some protection from the hottest sun, they’ll develop the brilliant fall colors ‘Vitifolium’ is famous for and will likely remain healthy for many years.
Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.