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.
The common ash is the last of the native broadleaf species to put on foliage in the spring and drops its leaves, made up of leaflets in opposite pairs, with the first night frosts. The seed bunches remain on the trees well into winter until ice and wind tear them off. The pale-coloured timber is hard and durable, favoured for making tools, sports equipment, furniture and parquet flooring. One of the olive (Oleaceae) family, the seeds and leaves have been used in traditional cures for many diseases. Coppiced branches were also used as winter cattle fodder at least until the early 1900s.
The finest ashes at Mustila grow on the western parts of Pähkinärinne (Hazelnut Slope). These trees may be threatened by a disease known as ash dieback (Hymenoscyphus pseudoalbidus), which has spread throughout Europe; there are already some branches showing worrying symptoms. There are definite sightings of the disease in south-west Finland.