In autumn, the green ash foliage turns brilliant yellow.
Green ash foliage
Green ash is a medium sized deciduous hardwood that can get up to 70 ft (21 m) tall and just as wide when grown in the open. The trunk is tall and slender and clothed in a grayish brown bark with interlacing ridges that form diamond shapes. The slender branches are upright and spreading and the tree develops a handsome rounded crown. The deciduous leaves, about a foot (30 cm) long, are pinnately compound with 7-9 (usually 9) lance shaped, sharply tapered 3-6 in (7-15 cm) leaflets. The petioles on lower leaves have narrow wings, and this is one way to distinguish green ash from white ash (F. americana) whose leaf stalks are not winged. Green ash leaves are olive-green to yellowish green on top and pale green (never whitish) underneath. They turn clear yellow in fall. Ash leaves are arranged opposite each other on the stems, and this is a quick way to differentiate an ash from one of the hickories, whose compound leaves are alternate. Small, inconspicuous flowers, which lack petals, appear in clusters in early spring before the leaves come out. Male and female flowers are borne on separate trees. The fruit is an elongated single-seeded samara with a single wing, reminiscent of one-half of a maple samara. Carried in clusters, they start out green, ripen to brown, and then flutter to the ground in fall, sometimes persisting on the tree into the winter. Green ash produces a large seed crop almost every year.
Green ash is a popular landscaping and shelterwood tree and several cultivars have been named. ‘Emerald’ and ‘Marshall’s Seedless’ are male clones that do not produce seeds. ‘Cimmzam’ is unique in that its autumn foliage is brick red rather than yellow. ‘Urbanite’ is a smaller tree, compact and cone shaped, with leaves turning bronze in fall and more tolerant of urban conditions than others. ‘Aucubifolia’ has leaves mottled with yellow, and ‘Variegata’ has silvery leaves with whitish margins.
Green ash (Fraxinus pennsylvanica) occurs naturally in eastern North America from Nova Scotia south to northern FL and west to central TX and southern Alberta. It is the most widely distributed of the North American ashes. Natural stands of green ash are confined to bottomland forests, along streams and in swamps: places that are subject to periodic flooding.
Culture Light: Plant your green ash where it will get full sun. Moisture: Like most of the ashes, green ash likes a neutral to alkaline soil that is moist. Green ash can tolerate inundation for as much as 40% of the growing season. This is not a drought tolerant tree. Although green ash grows naturally only in swamps and river bottoms, once established, it does very well in upland soils.
Hardiness: USDA Zones 3 -9. There is substantial variation in cold hardiness, dependent on where the trees come from. Green ashes from the southern part of the range may be hardy only to zone 5 or 6; those from the north, to zone 3 or even 2. The hardiness of cultivars varies as well. Some are hardy only to zone 5. The cultivars ‘Bergeson’ and ‘Patmore’ are possibly hardy to zone 2. Propagation: Under natural conditions, ash seeds lie dormant on the ground through their first winter and then germinate in spring. Seeds should be sown outside in the fall as soon as they are collected. It is not necessary to remove the wing from the samara. To store seeds, gather samaras when they are brown and spread out to dry completely. Dried seeds may be stored for years, but they are dormant and must be warm-stratified and prechilled before they will germinate. Hold dried seeds at 68°F (20°C) for 60 days, then at 32°-41°F (0°-5°C) for another 60-150 days prior to sowing in the spring. Named cultivars of green ash are grafted onto seedling rootstock.
'Marshall's Seedless' green ash trees line the play fields at the Boone County Arboretum in Northern Kentucky.
Green ash tree bark
Green ash is very adaptable, tolerant of extreme cold and heat; exposed, windy sites; urban conditions; coastal sites and salty conditions; heavy soils; nutrient-poor soils; and alkaline soils. This is a very popular landscape tree in eastern North America. It makes an excellent shade tree in the home landscape, and a fine street tree in town. They are often planted as specimen trees in parks. Green ash is one of the first trees to change color in the fall, and the golden yellow foliage can be quite attractive. Green ash is widely planted in shelterbelts in the Great Plains from ND to TX, and is one of the commonest street trees in the Midwest. You can avoid messy fruit litter by choosing non-fruiting cultivars. Also, be aware that many of the cultivars available in the trade were selected from northern stock and do not do well in the south.
The wood of green ash is like that of white ash; it is heavy and tough, and used for baseball bats, tool handles, snow shoes, paddles and other applications requiring a strong wood. The seeds are an important food source for squirrels and other rodents and for many kinds of birds, including cardinals, wild turkeys, wood ducks and quail.
It may seem surprising that a tree that occurs only in soggy swamps and flood-prone bottomlands in nature can do so well when planted in well drained upland soils. The thing to remember, though, is that plants do not grow where they WANT to grow, but rather, where they CAN grow. Most trees cannot grow in soils that are flooded for several months of the year. They simply drown. Green ash (and baldcypress (Taxodium distichum), for another example) can grow in such situations, but are out-competed by other trees on the drier, better sites. Remove the competition from those other trees, and the wetland species do just fine; better, even. Green ash and baldcypress do much better on fertile, well drained upland sites than they do in the wetlands where they naturally occur. They grow faster, bigger, and healthier. Consider also the sand pine (Pinus clausa), which occurs naturally on the deep, infertile pure white “sugar sands” of Central Florida where almost no other tree species can survive. But plant a sand pine in rich, fertile soils with adequate moisture, and it grows faster, bigger and healthier than it ever would on those sterile white sands. The sand pines don’t occur naturally on the more fertile sites because other trees simply out-compete them. Most tree species grow best in fertile, well drained upland soils with full sun, but the competition there is intense. Only some trees can tolerate less-than-ideal conditions, and that becomes their niche in nature.
Green ash was formerly considered a variety (called Fraxinus pennsylvanica var. lanceolata) of red ash (F. pennsylvanica), based on minor differences in the leaves. However, on closer scrutiny the differences do not hold up, and trees with intermediate characteristics are common. Why the whole species is now called green ash instead of red ash is a good question.
The genus Fraxinus has about 65 species, of which about 20 are native to the US, with the rest mainly in temperate Europe and Asia. A few occur in the tropics. All the ashes are deciduous trees except shamel ash (F. uhdei) from Mexico and Central America.
Green ash tree populations in the upper Mid-west and North Eastern United States are under severe attack by the emerald ash borer. Read more about this pest at emeraldashborer.info