Species: Pterocarya fraxinifolia
Common names: Caucasian wingnut, Caucasian walnut Swedish name: kaukasisk vingnöt
The genus Pterocarya is often called wingnuts in English. They are native to Asia. The botanic name is pteron meaning wing and karyon meaning nut or fruit. Pterocarya are large deciduous trees, with pinnate, feather-like leaves. They are monoecious and the flowers are attached on catkins. The seed catkins when mature are pendulous with seeds strung along them. The seeds are small nuts, with two wings, one each side. Wingnuts are very attractive and fast-growing trees, most common in parks and large gardens. Pterocarya fraxinifolia is one of the most used species in cultivation and horticulture.
Description: Pterocarya fraxinifolia grows to a height of < 30 m, and have a wide, airy, rounded form of the crown. The ash-like leaves can exceed 60 cm in length. The leaves turn butter-yellow in autumn. The flowers appear in spring (April), the male catkins are thick and green, while the female catkins are longer with less dense flowers, bearing red styles. The females develop into 30 – 50 cm long seed catkins, which bear the green, winged nuts. Pterocarya fraxinifolia has an exotic look that I love. The horizontal branches contribute with shade where the light filters through the foliage. It is at its best grown as a solitary near water, like a pond, river or brook. Where the branches reach over the water and the catkins hang down. The buds are wing-like and fascinating.
How to grow: Pterocarya fraxinifolia is fast growing and grows best on flat ground or shallow slopes near river banks and in deep moist soils. It prefers full sun or partial shade. Pruning should be done with care and to a minimum. The wingnuts are “bleeders” which mean they have to be pruned in the right time. In Sweden we recommend pruning during JAS (July, August, September) so summer is the best time. Older individuals of Pterocarya fraxinifolia may set of shoots from the roots (sucker). These can be removed during the summer.
Trees for small gardens and containers
The wingnuts are probably not among those trees most of us can grow. It requiers its space and many trees do. But it is not impossible to find small trees suitable for small spaces. Trees add hight and shape so do not forget them. Let me give you some examples to get inspired by:
- Salix caprea ‘Pendula’ – Kilmarnock willow
- Salix integra ‘Hakuro Nishiki’ – Japanese variegated willow or dappled willow
- Acer palmatum – Japanese maple (small varieties)
- Ribes rubrum – redcurrant tree form (many berries can be bought in tree form)
- Malus domestica ’Bolero’ – apple columnar tree
- Espaliered fruit trees – cherry, plum, apple, pear, peach etc (great as “room” dividers)
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