The Manchurian ash resembles the native Finnish species, the European ash (F. excelsior), but its leaves are considerably larger and the shoots thicker; as if painted with a broader brush. The previous year’s shoots are bluntly angular. The wind-pollinated flowers appear before leaf flush and are polygamous, i.e. each tree can have flowers with male and female organs, or flowers which are only male or female, or any combination of any or all of these.
This ash grows in moist rich soils on hillsides and in river valleys over a wide range which extends from western China to Korea and the Russian Far East. The provenances grown in Finland are from the north-east parts of this range and there are two distinct forms: var. rhynchophylla has leaflets which are oval and come to a point, like most ashes; and var. densata, whose leaflets are large and broad, almost round, with a sandpapery rough surface.
The dioecious (i.e. individual trees are either male or female) red ash is native to North America, where it has the greatest range of any of the ash species. It has also been long grown in Finland, having proved hardier and less demanding than the native common ash (F. excelsior). The red ash has an attractive habit and is widely used in streets and parks.
The Japanese ash is a form of Manchurian ash growing naturally on the northern Japanese islands of Honshu and Hokkaido, as well as on Sakhalin Island. On the cool mountain slopes it tends to concentrate in moist sites at the edges of mires or along rivers, with conifer forest dominating drier sites. Highly valued for the attractive patterning of its timber, the Japanese ash has become rather rare in the wild because of over-exploitation.
European ash grows naturally in southern Finland, but is the most demanding of all the native broadleaf species with regard to where it grows. It develops best on rich, very moist slopes. The northernmost parts of its range are wet bogs where there is movement of ground water. When planted, the ash survives somewhat further north, especially on protected sites, but for park plantings even central Finland demands hardier ash species from North America or Asia.