Magnolias
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Although it serves as an introduction, it almost goes without saying that few flowering plants rival the magnolias for sheer weight of bloom, beauty and delicate colour. Because they combine so many desirable characteristics, are mainly hardy while also being large enough to make a considerable impact on the landscape, magnolias should be considered pre-eminent among the large shrubs and trees suitable as foundation plantings.
Magnolias, which are named after an obscure French botany professor Pierre Magnol (1638–1715), are among the oldest flowering plants and can be traced back at least 100 million years. Some species, especially the very primitive M. hypoleuca from Japan, develop cone-like seed pods that are reminiscent of plants, now extinct, that bridged the gap between the conifers and cycads (Gymnosperms) and the flowering plants (Angiosperms).
At times during their long history the magnolias enjoyed a wide natural distribution over the northern hemisphere. Now, however, the genus is confined to Asia and North America.
The first magnolia to enter cultivation in European gardens was M. virginiana, the sweet bay, from the eastern United States, which arrived in Britain in 1688. This species, now not widely planted, can grow to over 15 m high although it is usually seen as a large shrub. It is semi-deciduous (or semi-evergreen if you like) and has 7.5 cm wide, fragrant, creamy-white flowers from late spring to autumn.
The sweet bay was followed by the similar and now far more common southern bay (M. grandiflora). This species occurs in much the same natural range as M. virginiana and is a large evergreen tree with magnificent leathery leaves that would make it a valuable foliage plant even if it never flowered. However, it does flower, and what a flower — cream, up to 25 cm in diameter, and marvellously scented. What’s more it blooms throughout the warmer months and in mild areas may have flowers throughout the year. Many forms are now available, some with the emphasis on large flowers, while others like ‘Ferruginea’ with its rusty red indumentum have foliage as their prime attraction.
The genus Magnolia includes deciduous, semi-deciduous and evergreen trees and shrubs. Most of the common garden plants are deciduous and are derived from Asian species. The first of these to be widely grown in Europe was M. heptapeta, which is still widely known, grown and sold as M. denudata. This species, introduced in 1789 by Sir Joseph Banks, had been cultivated in its native China for at least 900 years prior to its arrival in Europe. Commonly known as the lily tree or yulan, this species has pure white, goblet-shaped, spring flowers that are delicately scented.
The closely related M. pentapeta (M. liliflora), also from eastern and southern China arrived shortly afterwards and was quickly accepted into cultivation. This species, which is still widely grown, has somewhat strappy-petalled bright purplish-pink flowers in spring. The dark purple form ‘Nigra’ is more likely to be seen than the true species.
When these two species were crossed they gave rise to M. × soulangeana (often spelt soulangiana). This French hybrid, named after Etienne Soulange, first appeared around 1820 and has since been used to produce many garden cultivars. For many years if New Zealand gardeners thought or talked of magnolias the chances were they meant M. × soulangeana cultivars. However, new releases are now overshadowing the older hybrids and are quickly supplementing them in cultivation. I hesitate to use the word replacing as magnolias seem to go on virtually forever and there is no reason to suspect that M. × soulangeana will disappear. Popular cultivars, such as the deep pink ‘Rustica Rubra’, the white ‘Lennei Alba’, the two-toned white and purple ‘Brozzonii’ and ‘Norbertii’ and the quick-growing ‘San Jose’ will continue to be propagated and sold.
Many of the newer cultivars are of New Zealand origin and many of these have been produced by the Jury family who are also well known for their work with camellias. The Jury magnolias, of which ‘Mark Jury’, ‘Iolanthe’, ‘Star Wars’ and ‘Vulcan’ are probably the most popular, have very large flowers and bloom heavily from an early age. ‘Mark Jury’, the original hybrid, was found among a batch of seedlings imported from the Hillier Gardens in Hampshire, England and is the pollen parent of many of the other Jury hybrids.
Magnolias can take many years to bloom when raised from seed, but are quicker to flower when raised from cuttings or grafts. Nevertheless the fact that the Jury magnolias bloom at as little as five years old is surprising considering that ‘Mark Jury’ is thought to be a cross between M. campbellii ssp. mollicomata ‘Lanarth’ and M. sargentiana ssp. robusta, both of which are very slow to reach flowering age. Indeed, M. campbellii usually takes the longest of all, up to 40 years, although the subspecies mollicomata is known to bloom as young as 12 years old.
Magnolia campbellii, which can develop into a 25 m high tree, is one of the first magnolias to bloom in spring and may have a few flowers open by late July. In mild areas it can make a tremendous show, but all too often its flower display is ruined by frosts. The Jury magnolias bloom somewhat later, around late August onwards, and are less prone to such damage.
Although the Jury magnolias and others with M. campbellii parentage are impressive plants, some gardeners find their flowers too large and overbearing. For them the more delicate blooms of the star magnolia (M. stellata) have more appeal. Old specimens of M. stellata can become tree-like, but this species is generally smaller than most of the common magnolias. It is usually seen as a bulky shrub about 2.5 m high and wide. From late winter M. stellata produces masses of delicately scented, strappy-petalled, white flowers. Double-flowered forms, such as ‘Waterlily’ are available, as are pink flowered forms, but for grace and elegance the true species is hard to beat.
Of the 125 or so species of magnolias few, other than those already mentioned, are widely cultivated in New Zealand gardens. This is a pity because many of the species make attractive and unusual garden plants and often have the bonus of fragrance. Magnolia sieboldii is one that definitely merits wider planting. It has scented, pure white flowers in spring and early summer, which are contrasted by the pinkish-red stamens. Unlike most magnolias, which hold their flowers upright, those of M. sieboldii hang gracefully and are best seen from below. This is a great advantage because the beauty of magnolia flowers is often lost when they are high up in the tree, unable to be viewed from above. M. sieboldii is slow-growing and seldom exceeds more than 4–5 m high. It blooms young and will often have quite a weight of flowers even when still a small shrub.
Our garden magnolias have always tended towards white with pink and purple shades but recently several yellow-flowered hybrids have been introduced. Of these ‘Yellow Bird’ is probably the brightest coloured. It is still a fairly pale yellow but is a considerable improvement in colour and flower size on its parent, M. acuminata. Although not common there are a few good specimens of this species, also known as the cucumber tree, in our larger parks and gardens. One that I am familiar with in the Christchurch Botanic Gardens is easily 12 m high and flowers reliably every year but you could be excused for failing to notice its small greenish-yellow blooms.
Several other genera are closely related to the magnolias and make interesting and compatible companions for them. The michelias closely resemble magnolias and doubtless many gardeners overlook them thinking that they are nothing more than just another form of magnolia. However, they have a beauty all of their own. The two common species, M. doltsopa and M. figo, are quite different from each other. Michaelia doltsopa is almost evergreen, though slightly frost tender, and has very magnolia-like, cream, cup-shaped flowers in spring. It eventually grows to about 7 m high. M. figo is also evergreen, somewhat more tender and becomes a large shrub around 3 m high and wide. It flowers later and has strongly scented, small, cream and purple flowers. The fragrance is very fruity and has been likened to ripe bananas or grapes. The combination of scent and flower colour gives rise to its common name: port wine magnolia.
One of the magnolias closest relatives is the 20 m high tulip tree, Liriodendron tulipifera. Its yellowish-green and orange flowers are rather magnolia-like, but are usually so high up in the tree that they are hardly noticeable. The main attraction of this tree is its unusual deeply lobed foliage, which often turns bright yellow before falling in the autumn. There is a very attractive and distinctive variegated form called ‘Aureo Marginatum’ with leaves that have a broad cream margin.
The Carolina allspice, Calycanthus floridus, and the closely related C. occidentalis both have strongly fragrant reddish brown flowers in early summer and large deep green rounded leaves. The general appearance is rather like a red-flowered magnolia. All parts of the plants are aromatic. C. floridus grows to about 2 m × 1.5 m while C. occidentalis may reach 4 m × 2.5 m. They are unusual and attractive deciduous shrubs that are hardy and easily grown almost anywhere.
Choosing plants and caring for them
Because of the amount of time that seedlings may take to reach maturity it is always best to buy named varieties that have been vegetatively propagated. These may be cutting-grown, layered or grafted, but regardless of the method used they will flower at a considerably younger age than seedlings. Indeed it is often possible to buy plants in bud or flower.
Large deciduous magnolias are often field grown then lifted and potted for sale. This procedure is always a shock to the plant and inevitable checks growth to some extent. If possible, delay buying your magnolias until they have some new spring foliage and are clearly making strong growth. Also, as the plants have rather brittle roots, it pays to make sure that it is firm in the container and that it can hold itself upright without staking. A wobbly plant with a weak branch structure is likely to be already root damaged or more prone to root damage through wind-rock.
Magnolias prefer moist woodland soils and as with all plants that grow in such conditions thorough preparation of the topsoil and providing ample humus are the keys to success. A position sheltered from strong winds and protected from the hottest afternoon sun will yield the best foliage and longest flower display. Magnolias are, however, very adaptable and provided they are not exposed to long periods of drought or very deep shade they will tolerate most garden situations.
Start by digging a hole at least twice the width and depth of the root ball. Next work in plenty of high-humus compost or leaf mould. Magnolias prefer an acid soil and a light dressing of acid plant food is beneficial at this stage. However, no more than a handful or two thoroughly blended with the compost.
Place the plant in the hole and check its level. Grafted plants must have the graft union above soil level, taking into account the depth that may be provided by any future mulching. Firm the magnolia into place and mulch well with bark chips, compost or whatever is your favourite mulch — not mushroom compost, though, as it is usually too alkaline. Large specimens will need staking until they are well-established. Magnolias have soft bark and easily bruised stems, so use very soft ties and cushion the stem against the stake with a pad of cloth.
Although magnolias generally prefer an acid soil some are lime tolerant. The very vigorous M. kobus along with M. pentapeta, M. sieboldii and the M. grandiflora cultivars are all worth trying, but don’t expect their foliage to be as large or lustrous as it is when the plants are grown in moist, acid soil.
Regular watering, feeding and mulching should ensure quick establishment and rapid growth. Often, young magnolias will produce very strong-growing water shoots from the base of the plant. These should be removed, as should any growth coming from below the graft.
Magnolias rarely require heavy pruning. A general shaping and thinning is usually all that is necessary. The best time to cut them back is usually after the main flush of flowers, which, for most species, means around early December through to the end of January. Try to avoid cutting back too heavily as this will encourage water shoots to form.
Once established, magnolias require minimal care and will largely look after themselves. That these beautiful and rewarding plants are so undemanding is one of the greatest advantages, so it is not surprising that magnolias have always been popular and show no signs of becoming victims of the whims of gardening fashion. Long may it be that way.
Copyright Geoff Bryant
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