Plant of the Month: April

Magnolia x loebneri 'Merrill' Family: Magnoliaceae Vital statistics Height and spread: To 10m (34ft) high and wide Form: Tree Soil: Moist, well-drained, acid or alkaline soil Aspect: Full sun to partial shade Hardiness: Hardy throughout theBritish Isles

The plant at Rosemoor is situated at the south-eastern end of the old woodshed, adjacent to Rosemoor House in Lady Anne's Garden. The plant is ideally situated here to gain maximum benefit from the shelter of the wooded hillside to the east and the house itself to the west. This means that, in the event of frost, the sun does not reach the tree until well after the rime on the flowers has had a chance to melt.

Magnolia

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 that little evolutionary change has taken place. 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 at 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.

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.

Of garden origin, Magnolia x loebneri results from a cross made between the Japanese magnolias M. kobus and M. stellata. The initial work of hybridising was carried out by Max Loebner, garden inspector at the Bonn Botanic Garden, though much hybridisation has occurred since in America and Britain. It is a very variable hybrid, uniting the best qualities of its two distinguished parents. Several selections have been made and named including 'Leonard Messel', 'Merrill', 'Neil McEacharn' and 'Snowdrift'.

Magnolia x loebneri 'Merrill'

Described as an outstanding selection, Magnolia x loebneri 'Merrill' was raised by Dr Karl Sax in 1939 at the Arnold Arboretum, USA and named after Professor Elmer Merrill, a former director of the arboretum.

It is a small vigorous tree with large, white, fragrant flowers, freely produced before the leaves in mid-spring. The flowers are initially goblet-shaped but open to a star-shape with 15 broad, pure white petals.

AGM

The RHS Floral Committee B awarded Magnolia x loebneri 'Merrill' an Award of Garden Merit and described it as: 'Small deciduous tree with oblong leaves. Flowers white, to 10cm wide, with about 15 obovate tepals, opening before the leaves. Very free-flowering.'

Cultivation

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

Most species are best positioned with shelter from wind and frosts since the branches are brittle and the blooms can become damaged by late frosts. However, Magnolia x loebneri is one of the hardiest magnolias and can remain undamaged while others growing around it may succumb.

Magnolia x loebneri cultivars are remarkably tolerant of a wide range of soil types, from acid to alkaline and from light sand to a moisture-retentive (but not waterlogged) clay. They 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

The Magnolia Society

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

The RHS Rhododendron, Camellia and Magnolia Group
Founded in 1945, this group is for all RHS members who share an interest in rhododendrons, camellias, magnolias and associated plants.