Gardens

RHS Garden Harlow Carr

Plant of the Month: March

Name: Magnolia campbellii subsp. mollicomata Common name: sweet bay Family: Magnoliaceae Vital statistics Height and spread: To 15m (50ft) high to 10m (33ft) wide Form: Deciduous tree Soil: Moist, well-drained, humus-rich, acid to neutral soil Aspect: Sun or partial shade Hardiness: Fully hardy

Take the path out of the model village, walk past the bird hide and on to the willow dear. Walk past the large conifers to the right and the layed hedge and into the pinetum. Where the path forks up to a little summer house on the edge of a coniferous plantation, the magnolia is just before it.

Planted by Geoffrey Smith, the tree is approximately 35 years old and has reached a height of about 9m (30ft). Growing in an open position and given warm spring weather the flowers open in early March and last for about two weeks.

Magnolias

Magnolias are among the most ancient of the flowering plant genera. Fossil remains of the simple Magnolia flowers have been found in rocks belonging to the Tertiary period (2-65 million years ago) and show little evolutionary change. Today there are around 125 species of deciduous and evergreen magnolias from both the old and new worlds, including North and Central America, the Himalayas and Asia.

Magnolias were named after Pierre Magnol (1638-1715) a physician and botanist who was professor of botany and director of the botanic garden, Montpellier, France.

Magnolias vary in size from large trees to small shrubs and are valued for their longevity and exquisite, often fragrant, blooms. Magnolias produce some of the largest flowers of any tree or shrub grown in temperate gardens, though some species take many years to flower, Magnolia campbellii will take up to 30 years to flower from seed and about 15 years for grafted or budded plants.

Magnolias also have a number of important uses. The timber from several species is used for various purposes and is prized for the close-grained, light yellow, soft wood which can easily be worked. Some species have been used for centuries in China as medicine. The bark and flower buds of Magnolia officinalis are used to cure coughs and colds and intestinal problems respectively. M. denudata is used as a food plant, the petals being used to flavour rice, and the bark has medicinal properties for treating colds. American species were also used as local medicines with the bark of M. grandiflora acting as a stimulant and tonic.

Magnolia campbellii subsp. mollicomata

Magnolia campbellii subsp. mollicomata is a geographical variant of M. campbellii from south east Tibet and south west China. It was discovered by George Forrest in 1904 amongst the drifting snows of the Mekong valley in Yunnan, south west China, in natural association with Viburnum, Daphne and Rhododendron species.

However, it was not until 1924 that it was brought into cultivation. It was found to be is similar in many ways to Magnolia campbellii but hardier and more dependable in the British climate. It flowers at an earlier age, some plants having been known to flower within 10 to 15 years from seed. It also flowers later in the season so it misses some of the spring frosts that would otherwise damage the open flowers.

A vigorous, conical then spreading deciduous tree Magnolia campbellii subsp. mollicomata has leaves similar to those of M. campbellii, being mid green and generally elliptic in shape but with more flattened hairs on the underside. The distinctive flowers, up to 30cm (12in) across, are borne in spring on leafless branches, the pink to rose-purple petals forming a beautiful cup-and-saucer shape with the outer row remaining horizontal while the inner row form a bulbous dome.

Fruiting is not normally an attraction with M. campbellii, but it is with subspecies mollicomata, which bears showy, long, bright red fruits in early autumn.

Cultivation

Magnolias are not difficult to grow provided that certain conditions are satisfied in siting, planting and management.

Most species are best positioned with the maximum shelter from wind as possible since the branches are brittle and the blooms can become bruised in the wind. Magnolia campbellii subsp. mollicomata is hardy, though the flowers and young foliage may be damaged by late frosts and severe cold winter weather can also cause shoots to die back.

Magnolias grow well in acidic, moist, well-drained, humus-rich soils and benefit from thorough ground preparation prior to planting to produce a rich, fertile loam. Never plant magnolias too deep - the top of the soil should match the existing compost level. Magnolias have fleshy roots which if damaged while not in active growth do not heal over sufficiently quickly. If a plant is potbound the roots should be carefully and gently teased out and planting postponed if necessary until the weather is warmer.

Unless specimens are being wall trained or become damaged, magnolias do not need pruning as a regular cultivation requirement. If pruning is required a good rule is to prune plants that flower in spring and early summer between late July and early September. Late flowering species should be pruned when growth begins in the spring.

Magnolias are generally free of pest problems, though young plants are vulnerable to attack by slugs, which if left unchecked can defoliate the plant.

Magnolias can be affected by several diseases. While highly resistant to honey fungus, plants under stress can become susceptible. In young specimens the leaves may become smaller and look chlorotic while larger specimens will gradually decline over several years.

Secondary infections can also lead to the decline of specimens after damage caused by frost (which causes the shoots to die back) or deer and rabbit damage where the bark may be gnawed.

Propagation

Magnolias can be successfully propagated from seed, cuttings, layering, chip budding and grafting.

Where open pollination has taken place, considerable genetic variation has been found in collected seed so plants rarely come true. Plants raised from seed will also take a considerable time to flower, although some hybrids raised from seed flower in under 10 years. The advantages of raising plants from seed are that exciting new cultivars can be bred and seedlings generally exhibit fast establishment and good growth.

Most magnolias can be propagated by cuttings. Deciduous cultivars and species should be raised using softwood cuttings taken in early summer while semi-ripe cuttings taken in late summer should be used to propagate evergreens.

Many commercial nurseries use chip budding and grafting to propagate named magnolias as large plants can be raised quickly this way. Grafting takes place between September and March while chip budding is carried out in July, when the plants are in growth.

More information

Click here to visit the Magnolia Society website

Gardiner, J, 2000. Magnolias, a Gardener's Guide. Portland: Timber Press