Sophora

In a suitable position, this largely trouble-free exotic tree can make a striking point of interest.

Sophora tetraptera AGM - photo: Adrian Thomas
Sophora tetraptera AGM - photo: Adrian Thomas

One of the highlights for tree lovers at the Royal Botanic Gardens, Kew is a 250-year-old Japanese pagoda tree, the Sophora japonica Award of Garden Merit (AGM). It is said to be one of the original five trees obtained for Kew from Asia and planted in 1760. It still flowers beautifully, and despite its name, came from China originally but was planted near Japanese Buddhist temples.

The genus is part of the Papilionaceae family and S. japonica AGM flowers in August to October, which is rare for a tree. It is also quite beautiful, both in flower and habit.

With a spread of 20m this variety needs a parkland setting, although the London Olympics in 2012 may provide an opportunity to use it because it is an excellent shade or street tree, creating a gentle filtered light rather than dense shade.

It also holds its foliage well into autumn. In urban environments it has proved a match for London plane trees in terms of durability, the only downside being that it can take a number of years to produce flowers.

An unusual cultivar is S. japonica ‘Pendula’, which has mounds of drooping branches, making a fine lawn specimen or natural arbour. It has a height and spread of about 3m, and although it rarely flowers its foliage is attractive.

Aside from southern Asia, the genus itself is native to south-eastern Europe, Australasia, the islands of the Pacific Ocean and South America. There are also perennials or smaller evergreen trees or shrubs in the genus, but few wholesalers stock many sophoras apart from S. japonica. One exception is the compact S. Sun King AGM, which is respected for its long-lasting golden-yellow winter flowers.

Only one other Sophora has an AGM tag — S. tetraptera or Kowhai from New Zealand, with golden-yellow flowers in late spring. It is an evergreen small tree or shrub, growing to 10m tall, and more suitable for warmer parts of the country as it is a little tender.

Sophora can grow in any soil that is well-drained and moderately fertile, and is extremely resilient to urban pollution. It is also untroubled by pests or diseases.

To grow and flower well, they need a protected site or a sunny wall, especially when grown away from the mildest parts of the country. Transplanting older plants needs to be undertaken with care as they dislike being moved. As the flowers are produced on the current year’s growth, only minor pruning is usually required, which is best undertaken not long after flowering to avoid cutting off future flower buds.

Propagation is from seed sown as soon as it is ripe — a pre-soaking in water is recommended to soften the hard shell. Semi-ripe cuttings of evergreen species are taken in summer or autumn.

What the specialists say

Matthias Anton, managing director, Deepdale Trees, Bedfordshire

“S. japonica Award of Garden Merit (AGM) is a tough tree for the urban environment, which survives with little water and grows in poor soil conditions, even on windy sites. It is not suited to the colder parts of the country, as it doesn’t like temperatures below –10°C.

“Unfortunately, landscape architects here don’t seem to like sophoras, but the rest of Europe loves them. I’m a big fan and would like to see more of them planted. Although it takes a while for sophoras to flower, I’ve seen them in flower from around 12- to 15-years-old. They form a lovely structure, have beautiful flowers, interesting pinnate leaves and a nice texture to the bark, which I really like.

“We sell standards up to a girth of 30cm and multi-stemmed S. japonica AGM, which forms lovely billowing, mushroom shapes eventually reaching 15-20m tall.

“We also sell S. japonica ‘Regent’, which is grafted, so is more uniform and ideal for avenues. It is the same as S. japonica AGM, with creamy-white flowers and a dark, shiny green leaf, and is also extremely resistant to urban pollution or heat — it’s just more upright.”

Steve Dance, office manager, Burncoose Nurseries, Cornwall

“We sell Sophora propagated from cuttings by mail order. They are quite popular because their yellow flowers are something a little unusual for the winter.

“They also have good foliage that is attractively pinnate and can be quite delicate, although all the foliage is pretty much the same throughout all the different species and cultivars.

“A very popular one is S. Sun King AGM, which is a lovely evergreen shrub with bright golden-yellow flowers. It might be a bit tender, but given a sunny wall it will grow to about 3m and flower reliably between late winter and early spring.

“We also sell S. microphylla ‘Dragon’s Gold’, which has nice yellow flowers and dark green lacy foliage. Generally, I think, to get decent flowers they should be grown on a south-facing wall, in a sunny position.

“We also offer S. tetraptera AGM, which comes from New Zealand and is quite showy with its clusters of tube-shaped yellow flowers between May and July, which is a little earlier than the others.”

In practice

Aaron Bertelsen, gardener, Great Dixter House & Gardens, East Sussex

“Sophoras remind me of my home, New Zealand, where they grow in large groves that turn into a mass of beautiful yellow flowers — Kowhai is actually the Maori word for yellow. They are one of the country’s seasonal highlights.

“At Great Dixter we only grow S. ‘Little Baby’. It’s planted in our tropical garden, which is quite compact, so it has to be a very good plant as it’s got a lot of intense viewing to live up to. We use it alongside Verbena bonariensis AGM. The foliage of S.‘Little Baby’ is made up of little rounded leaves and is very fine, so together they make a light and airy display.

“It’s a great plant as it’s very compact, doesn’t get out of control and has, like many of them, zig-zag branches. The only pity is that the flowers come out in the winter when the garden is closed to the public. But it is a wonderful foliage plant.”

Species and cultivars

•    S. davidii is a deciduous shrub growing to 2.5m tall with tiny grey-green leaves. In spring it displays racemes of 15cm-long purple-blue and white flowers. To grow well it needs a sunny, protected position.
•    S. flavescens is an evergreen shrub with yellow flowers in late summer. It needs a warm, sunny location and is an important medicinal plant in China with wide-ranging uses, having anti-bacterial and antifungal properties.
•    S. japonica Award of Garden Merit (AGM) or Japanese pagoda tree is a spreading tree for streets or parklands, reaching 30m tall with a 20m spread. It is deciduous and has glossy, dark green leaves, which turn yellow in autumn. It was once widely planted for its fragrant, 30cm-long panicles of white flowers in late summer or early autumn.
•    S. japonica ‘Pendula’ is a very attractive weeping cultivar with pendulous branches. It makes an excellent lawn specimen, growing to 3m in height and spread but rarely flowers.
•    S. japonica ‘Regent’ is an upright, more uniform grafted version of S. japonica. It is ideal as a street tree or avenue.
•    S. ‘Little Baby’ is a smallish shrub from New Zealand with narrow, wiry stems, growing in a zig-zag fashion. Orange-yellow flowers are produced in winter. To grow well, it needs a warm and sheltered spot.
•    S. macrocarpa is an evergreen shrub or small tree from Chile with short racemes of yellow flowers. It needs a warm and sunny site.
•    S. microphylla is a small evergreen tree or shrub from Chile and New Zealand that grows to about 8m tall and wide. It has dark green leaves and clusters of pendent yellow flowers.
•    S. microphylla ‘Dragon’s Gold’ is a small, evergreen tree or shrub with lacy dark green foliage and tubular, golden-yellow flowers.
•    S. microphylla ‘Early Gold’ is a small, evergreen tree or shrub that has fine, elegant foliage and soft lemon flowers in early spring.
•    S. microphylla var. fulvida is a small, evergreen tree or shrub displaying golden-yellow flowers.
•    S. microphylla var. longicarinata is a small evergreen plant with lemon-yellow flowers.
•    S. prostrata is a low-growing species reaching roughly 1m high and featuring a mass of tangled branches and bright yellow flowers.
•    S. Sun King AGM is a hardy cultivar that grows to around 3m tall and carries long-lasting bright yellow flowers from late winter to spring.
•    S. tetraptera AGM or Kowhai is a spreading, evergreen tree or shrub growing to 10m high and 5m in diameter. To grow well it needs a warm sunny wall. In late spring, 6cm-long racemes of gold yellow flowers are produced.
•    S. tetraptera ‘Grandiflora’ has larger flowers.


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