Magnolia grandiflora L.

Magnolia grandiflora is one of the great broadleaved evergreen trees of temperate zone gardens. In milder areas it can make a bulky, round headed tree, but the allure of its leathery, glossy leaves, typically with a lovely rufous indumentum beneath, and its long succession of big (sometimes huge) scented white flowers means that even in cooler areas gardeners have given over to it remarkably generous shares of precious wall space and sheltered corners. To Americans from the southern states it means much more: this plant is a symbol of the South.

Section Magnolia includes perhaps 27 species, all from Central and North America plus some Caribbean islands, but only this and two others are in anything close to general cultivation in our area, the tip of a largely tender iceberg. M. virginiana differs from M. grandiflora in being a smaller tree or shrub, deciduous in some forms, with smaller flowers and white or glaucous leaf undersides. M. tamaulipana is probably the closest relative of M. grandiflora, differing in its fewer stamens and carpels, shorter outer tepals, ‘dirtier’ flower colour and leaves with only minute hairs beneath.

The Bull Bay would have been a familiar tree to early European colonists in the South. Among the first Magnolia species to be described scientifically (Catesby 1743), Linnaeus’ specific epithet of 1759 refers to the large flowers, which had been seen in European gardens by the time Catesby was writing. It was well known to Native Americans of the southeast, bark extracts being used by the Choctaw and Kosati to treat swellings, itching and sores (Moerman 2021). Pre-colonial uses of the wood seem not to have been recorded. The timber is straight grained and easily worked, but not very durable. A light creamy colour, its main uses are in plywood and furniture frames, and as a veneer (Meier 2008).

In form this is a most variable tree. While it makes small scrubby plants growing among sand dunes overlooking the Gulf of Mexico, it is most often a large tree of rich, moist, well-drained soils (Outcalt 1990). Form and growth rate of seedlings is ‘incredibly variable’ (Gilman & Watson 1994): some are dense, making good screens, while others have widely spaced branches; some are as wide as they are tall, others almost columnar. Of several American champions, two have short, stout trunks branching low down to form wide crowns (in Smith Co., TX, 22.6 m × 635 cm, crown spread 24.4 m, 2020; and in Sussex Co, VA, 18.6 m × 676 cm, crown spread 18.6 m, 2016). A quite differently proportioned single-trunked tree in George Co., MS was measured at 33.8 m × 279 cm in 2012, its sparse crown spreading 21 m (American Forests 2021).

The foliage is notably heat-, wind- and drought-tolerant by the standards of large-leaved evergreens (Treseder 1978). Drought tolerance of the tree as a whole is better when there is space for a large root system to develop; good water availability is ideal, especially when grown in full sun (Gilman & Watson 1994). In SE Europe, Vastag et al. (2020) found the species’ physiological responses to drought much better than those of M. × soulangeana, which is far more often used locally in urban plantings, something to be borne in mind with climate change. The indumentum on the lower leaf surface might be expected to reduce transpiration. However, it is developed to a very variable extent. Cultivars with conspicuous indumentum have been selected for ornament, but studies of this variation in relation to drought tolerance and climate seem to be lacking. It is tolerant of alkaline soils, even thin soils on chalk in S England.

The flowers have a voluptuous lemon-like fragrance; their size is in keeping with the majestic foliage but again varies between clones, to 45 cm across in extreme examples. They vary in tepal number (9–15) and last 2–4 days, being cup-shaped on the first (female-fertile) day and saucer-shaped on the second (male-fertile). The stamens begin to fall during the male phase, making the flower appear less perfect. Many authors have focussed on beetles as pollinators of M. grandiflora (Thien 1974). However, a study in Louisiana populations found that bees (both indigenous species and honey bees) were more frequent visitors and effective pollinators whose behaviours correlated with changes through the life of individual flowers (Allain, Zavada & Matthews 1999). In North America the spring to summer flowering period is often more extended in garden plants (Jacobson 1996). In the maritime climate of the British Isles, late summer and early autumn is typical.

The red fruits are an ornamental feature in warmer climates, but are seldom produced in the cooler summers of Britain. The cultivar ‘Charles Dickens’ (probably a close hybrid, but often listed under M. grandiflora) is perhaps a better bet for conspicuous fruiting in maritime Europe. In the wild, seed is spread by birds and mammals, but sometimes also by water after heavy rain (Outcalt 1990). The fallen fruit ‘cones’ and large dry leaves are considered messy by the tidy-minded, and certainly do take a long time to decompose, but this seems a small price to pay for growing such a beautiful tree.

Seed was once the usual means of propagation in North America, with grafting a minority pursuit, but techniques for rooting cuttings are now well developed, allowing ready distribution of cultivars (Dirr 2009). Time from seed to flowering varies greatly between seedlings. Layering is also possible: the practice of pegging down the lower branches of specimens beside early Southern homesteads perhaps not only generated new plants but helped stabilize the tree in storms.

Southern Magnolia has come to symbolize the American South, which is as much a social construct as it is a geographical area. Inclusion of the word ‘Magnolia’ in a book or film title goes a long way towards establishing a setting, while characteristically Southern ideas and behaviours are said to come from ‘behind the magnolia curtain’ (Jackson 2017). It is the State Flower of both Mississippi and Louisiana, and its symbolism transcends the controversy around use of Confederate imagery, illustrated by the history of the Mississippi State Flag. On its secession from the United States in 1861, the state adopted a flag featuring a flowering magnolia tree – a statement of Southern distinctiveness – which was used through the Civil War. Throughout the 20th century, the flag carried instead the Confederate battle insignia, a source of increasing controversy, but this was replaced in 2021 by a design centred around the unifying image of a magnolia flower (Wikipedia 2021).

M. grandilfora was introduced to the British Isles early in the 18th century, certainly before 1728 (Treseder 1978), and probably around the same time to France and Spain. Until the advent of the Chinese M. delavayi it was the only really evergreen hardy magnolia available (Bean 1981). While it makes an admirable wall shrub, appreciating warmth and able to regenerate well after heavy pruning, it is widely hardy in the open in Britain, given sun and shelter. Most older examples probably represent a few early cultivars, such as ‘Exmouth’. Free-standing specimens are mostly in southern and western areas, including a lawn specimen at Powderham Castle (probably the same one mentioned by Loudon (1838) as already being 9 m tall) measuring 10 m × 264 cm in 2001 (The Tree Register 2021). In colder central areas, large specimens are more likely to be on a wall, for example at Leicester University Botanic Garden (10 m × 112 cm, 2015). For its extreme height, a specimen on a free-standing wall at Castlelough House, Co. Tipperary, Ireland is noteworthy (14 m × 186 cm, 2010 – The Tree Register 2021). Relatively low summer temperatures and the tendency of branches to break under heavy snow (Bean 1981) probably restrict its ultimate height in Britain.

Much taller specimens can be seen on the French Riviera and in N Italy. For example, a tree believed to date from the 1740s at Villa Zava, Vittorio Veneto (to the north of Venice) has estimated measurements of 19 m × 528 cm (2011/2016 – monumentaltrees.com 2021). The species is widely grown in the Low Countries – Arboretum Provinciaal Domein Bokrijk, Belgium holds a notable collection of cultivars (Plantcol 2021) – and into Germany, but Scandinavia seems to be a step too far even for hardier cultivars.

A classic for landscape plantings on the southern fringe of our American area, it can be grown up the Pacific coast as far as British Columbia, and on the eastern seaboard as far as the Boston area. Hardier cultivars are recommended for zone 6 (eg the St Louis area – Missouri Botanical Garden 2021). In Zone 5b this species is ‘something of a Holy Grail to the Zonal Denial Crowd’ (Cover 2004), but can be no more than an experimental plant for sheltered spots.

The experimental hybrids ‘Freeman’ and ‘Maryland’ confirm that M. grandiflora will cross with the diploid M. virginiana. Natural hybrids have been suspected where their ranges meet (Meyer 1997).

Cultivars fall into two main groups. A few old clones are of European origin, reflecting vegetative propagation of a limited number of early introductions. The bulk are of American origin, widely distributed only since the 1970s when clonal propagation became frequent, and reflect the species’ diversity of crown form, hardiness, leaf indumentum and floral characters.