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The Garden
March 2006

Stellar attraction

Among the most desirable magnolias for the garden, Magnolia stellata and its relatives are available in several choice selections. Jim Gardiner picks the best

Images: Tim Sandall & Jim Gardiner (Magnolia stellata 'Waterlily)

There are few sights in the year more assuring, or beautiful, than a magnolia in full blossom, its immaculate ‘petals’ shivering in the breeze. Spring has arrived at last. One of the most popular is Magnolia stellata (star magnolia) (left), one of six Japanese species. It has a compact, twiggy habit ideal for smaller gardens, and flowers that can be white or pink, with tepals (petal-like structures) varying in number from 12 - 40. They open over a four- to six-week period during March and early April, and can have a delicate scent.

It is uncertain who first introduced this species to the UK, however, it is most likely to have been Charles Maries in 1877 or 1878, when he was collecting for Veitch’s Nursery.

Wild origins

Magnolia stellata is a species found wild in sites of the Ise Bay area of central Honshu, Japan’s largest island, at low elevations between 50m and 600m. It grows by streamsides and in moist, boggy areas with other woody plants such as Enkianthus cernuus, Corylopsis glabrescens var. gotoana and Berberis sieboldii.

There is natural variation within M. stellata; flower colour varies from white to rich pink, and in some sites plants grow only to 3-4m, yet in other populations, on drier wooded slopes, they can reach 8-9m high. Several sites were threatened by industrial development but, during 1994, the Japan Association for Shidekobushi Conservation was established to help protect them.

There are two closely related species: M. salicifolia (Japanese willowleaf) and M. kobus. Magnolia salicifolia is an upright shrub or medium-sized tree, with small white flowers that often have a hint of pink at the base. Its willow-shaped leaves emit a scent of lemon verbena if crushed. It is the only species to overlap geographically with M. stellata in the wild, which sometimes results in a natural hybrid: M. x proctoriana.

Magnolia kobus (left) is common throughout the forests of Japan. It is a much ‘heavier’ plant than M. stellata, growing into a tree up to 18m tall. Generally it flowers earlier than M. stellata, in mid-March, with flowers composed of six white tepals up to 10cm long, often flushed pink at the base. No naturally occurring hybrids are found in the wild; however, once these two species are brought together in a garden situation, they will hybridise freely to produce M. x loebneri.

Flowers and frost

Despite having only three species, one naturally occurring and one garden hybrid from which to select, there is a surprisingly wide choice of plants for gardeners. All these magnolias are extremely hardy, tolerant of the coldest of weather conditions. Where certain plants may succumb is when individuals are exposed to a late-spring frost. Those growing strongly in spring, showing the first flush of growth in April, are vulnerable to a sharp air frost of -3 or -4ºC. Even mature plants will take a knock, which is especially noticeable after a dry winter.

Flowers will tolerate 2° or 3°C of frost, but M. stellata, M. x loebneri and the Janaki Ammal clones of M. kobus (see below) are the most resistant as their flowers open progressively over a period of several weeks.

Flower shape varies, depending on the outline and number of the tepals. Magnolia kobus ‘Norman Gould’ (left) and specific clones of M. x loebneri (such as‘Donna’ and ‘Merrill’ right) have broad tepals yet, by contrast, M. stellata ‘Chrysanthemiflora’ has narrow, strap-like tepals, giving the blooms a dainty appearance.

Pink magnolias will change hue from year to year, depending on day and night air temperatures prior to and during flowering. For example, in different years, the same plant of M. x loebneri ‘Leonard Messel’ may display flower colour anywhere between palest pink and rich pink; lower temperatures result in paler-coloured blooms.

Selecting Magnolia stellata

There are about nine clones of M. stellata commonly grown, varying primarily in flower colour and the number of tepals. What can be confusing is when the same name is applied to different plants. For example, ‘Waterlily’ (left) in the UK and Europe is a pure white, while the clone in North America is pale pink.

‘Centennial’ is a fine American clone with clean white, slightly larger flowers to 14cm across, with up to 33 tepals. It was raised at the Arnold Arboretum, Massachusetts, and named during its centennial year in 1972. ‘Scented Silver’ (right), another American clone, selected in 1973 but only introduced in 1990, is distinct in having a delicious lemony perfume.

‘Royal Star’ (left), also from the USA, is a ‘Waterlily’ seedling from 1960. Silver-pink in bud, the flowers open to pure white up to two weeks later than most other M. stellata clones, sometimes helping it to escape frost.

Plantsman Sir Peter Smithers, who lives in Switzerland, obtained a beautiful, rich pink-flowered plant from Wada’s Nursery of Yokohama in Japan. It has 32 tepals and is known as M. stellata ‘Rosea’ fine variety - differentiating it from commonly grown M. stellata ‘Rosea’.

Having seen this plant in Sir Peter’s garden, I rate it as the most sumptuous of all the clones, but unfortunately ‘Rosea’ fine variety does not produce flowers of the same intensity of colour in UK gardens. There are other named selections that resemble this clone, including M. stellata ‘Chrysanthemiflora’, M. stellata ‘Jane Platt’ (right) and M. stellata f. keiskei.

The Wisley connection

Doctor E K Janaki Ammal (1897-1984) was an Indian geneticist working for the Society at RHS Garden Wisley in the early 1950s. She was investigating the effects of colchicine on a number of woody plants, including Magnolia. Colchicine is an alkaloid extracted from Colchicum autumnale (autumn crocus). A stock solution in water is made up and applied to the growing tip of young seedlings once the cotyledons (seed leaves) have fully expanded. Doubling of chromosomes occurs, giving the cells twice the usual number. The resulting plants have heavier textured leaves; their flowers are variable, often with thicker tepals, helping them last longer.

As Magnolia kobus seeds were available in quantity, a number of seedlings were treated by Dr Janaki Ammal and ultimately planted on Battleston Hill at Wisley. After 50 years all are about 8m high and wide, with similar broad spreading habits. They are among the first magnolias to bloom (March) and are extremely prolific in the number of blooms. The number of tepals varies, from M. kobus ‘Norman Gould’ with nine broad, pure white tepals, to M. kobus ‘Wisley Star’ (one of the best) with 18 strap-shaped tepals.

Another M. kobus hybrid deserving wider attention is ‘Pickard’s Stardust’ which flowers for several weeks in March and early April. Introduced in the early 1960s, this compact-growing, floriferous plant was raised by Amos Pickard, a nurseryman from Canterbury.

Other related selections

Magnolia x loebneri is one of the most widely grown of all magnolias worldwide, thanks in part to its ability to grow successfully in many climates. The most popular selections of this hybrid today have been raised in Britain, North America, northern Italy, Korea and Japan. Ever-popular M. x loebneri ‘Leonard Messel’ (left) was a chance seedling raised at Nymans in Sussex in the 1950s. It is one of my favourites and the least vigorous, with reasonably frost-tolerant flowers of 12 rich pink tepals opening progressively during March and April. Korean M. x loebneri ‘Raspberry Fun’ (above) is similar but its flowers have 16 tepals and are clustered in twos and threes. Beautiful M. x loebneri ‘Merrill’ is a most vigorous American clone, forming in time a small, quite open tree. It has up to 14 broad white tepals, while M. x loebneri ‘Donna’ produces even larger, pure white flowers, yet has a denser, rather more shrubby habit.

Recently introduced M. x proctoriana ‘Robert’s Dream’ is a fine selection of this natural hybrid with a generally upright habit and dainty, pale pink flowers appearing from March onwards.

Garden use

Provided these magnolias have been vegetatively propagated (that is, not grown from seed), all can be expected to produce flowers within 18 months of rooting a green-wood cutting, which most gardeners should succeed with.

The plants’ eventual habit varies widely. Magnolia stellata is slow growing with most clones putting on around 30cm per year, developing into a compact shrub of 2m in height and spread after 10 years. Magnolia kobus and M. salicifolia tend to be quite variable, some growing vigorously, increasing by 75cm a year and developing into upright, spreading trees; others, however, remain compact, retaining a shrubby habit. Magnolia x loebneri is variable, too: ‘Leonard Messel’ slowly develops into a large shrub, while ‘Merrill’ can be a single-stemmed, small tree.

Magnolias can be pruned to maintain a desired shape if required but given a choice, I would generally not cut them, apart from carrying out formative pruning. However, I have seen M. stellata grown as a hedge, which can be trimmed in August. All these plants are relatively free of pest and disease attack.

All the species grow in acid soils in the wild, but will tolerate alkaline conditions, as long as the soil is moisture-retentive.

Plants have thick, fleshy roots which are found fairly close to the surface and do not like disturbance, enjoying an annual organic topdressing, though this is not essential. They like hot summers and flower more profusely in full sun, but are good performers in cooler climates. Autumn foliage colour can be quite noticeable, with M. salicifolia in particular turning a rich golden brown.

These magnolias grow happily with a range of woody shrubs. Chimonanthus praecox ‘Luteus’, Rhododendron dauricum ‘Midwinter’, Sarcococca confusa and many Daphne bloom before and during the magnolia flowering period. Later colour could be added with Rhododendron yakushimanum and its hybrids, many of the scented late-flowering azaleas such as Rhododendron viscosum or Rhododendron atlanticum, and later still, Hydrangea serrata, Hydrangea quercifolia or Hydrangea paniculata.

Small bulbs can be planted beneath, including mauve Crocus tommasinianus which will naturalise, flowering in spring; for autumn flowering, try Crocus nudiflorus. Other good subjects for underplanting, either to extend the season or complement the magnolias’ flowering, are Cyclamen hederifolium, Cyclamen coum, Anemone nemorosa, Corydalis flexuosa and our native Primula vulgaris (primrose).

Clematis, especially those pruned in early spring that flower in the second half of the summer, such as Clematis viticella, C. ‘Etoile Violette’, C. rehderiana and C. ‘Polish Spirit’, are all useful trained through the crowns.

Magnolia stellata and its related species and selections demonstrate that not all magnolias are the preserve of large gardens on acidic soil; these plants will prove first-rate garden plants in many situations.

Jim Gardiner is Curator of RHS Garden Wisley, and a former President of Magnolia Society International

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