Fraxinus pennsylvanica Seeds | Green Ash

Pinnate green ash leaves and hanging clusters of single-winged samaras — Green Ash (*Fraxinus pennsylvanica*): Oleaceae, flood plains and river banks of eastern North America.

LATIN NAME: Fraxinus pennsylvanica

COMMON NAME: Green Ash

Plant Profile

Green ash was, for most of the twentieth century, the tree planted along the streets of half of North America, and that is now the source of its problem. It is a tall, upright tree, fifteen to twenty-five metres, with opposite, pinnate leaves of five to nine leaflets, a straight grey trunk and a rounded, open crown. The flowers appear before the leaves in spring, small and wind-pollinated, and the fruit is a single-winged samara in hanging clusters that persist into winter. It is fast, tolerant of wet ground, drought, road salt and poor soil, and it transplants easily, which is why it was planted by the million in the years after Dutch elm disease. The bark is grey and furrowed, with a distinctive diamond pattern on older trunks. It grows on flood plains and river banks across eastern North America, from Nova Scotia to Texas.

Science & Biotechnology

Fraxinus pennsylvanica is a diploid, 2n = 46, and it is one of the ashes whose taxonomy has been muddled: the red ash, once treated as a separate species, F. pennsylvanica var. subintegerrima, is now generally included in the green ash, with differences in leaf hairiness and samara shape that intergrade. The species is dioecious, with male and female trees, and the widely planted cultivar Marshall is a male clone, chosen because it sets no seed and therefore does not litter pavements. The great threat is the emerald ash borer, Agrilus planipennis, a beetle from eastern Asia that arrived in Michigan in the 1990s and has killed hundreds of millions of trees across the continent, because North American ashes have no co-evolved resistance. Some Asian ash species show partial resistance, and breeding work is using them.

Uses & Benefits

The timber is tough, elastic and pale, and it has gone into tool handles, baseball bats, furniture, flooring and sports equipment for generations. It is also excellent firewood. As a street and shade tree it was invaluable for its tolerance of wet and compacted ground, and it is still planted where ash borer is not yet established, though that is a shrinking area. The samaras feed birds and small mammals in winter, and the foliage is food for the caterpillars of several native moths. The bark has a place in Chinese pharmacy as qin pi, used for intestinal heat, and the coumarins fraxin and esculetin are studied for anti-inflammatory activity. In North America, the tree is now mainly a conservation and replacement problem.

Growing from Seed

Sow in autumn and leave the pots outside, or give three months of cold, moist stratification at 4 degrees; germination is in spring and is usually good. The samaras can be sown as they are, without cleaning, and they need light to germinate, so cover them only thinly. Keep the mix moist and the seedlings in full sun. They grow fast, thirty to fifty centimetres in the first year, and they transplant well, even bare-root. Plant out at sixty centimetres to a metre in autumn, in sun or light shade, in any soil that is not permanently waterlogged. Water for the first two summers. If you garden where emerald ash borer is present, planting ash is an act of optimism; consider a resistant species instead, or plan for treatment.

Our Take

A fast, tough shade tree that has been devastated by emerald ash borer. Plant it only where the beetle has not arrived, and choose a male clone if litter matters.

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