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last updated Jan 12, 2011
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Magnolia

Magnolias are trees or shrubs with astonishing goblet- or star-shaped flowers that are admired icons of spring and summer. Evergreen magnolias are particularly good for wall-training.

Cultivation notes Back to top

Deciduous magnolias usually flower in spring before leaf emergence. Magnolia grandiflora (bull bay), the most commonly grown evergreen, flowers in flushes from summer until early autumn. In warm summers these can be followed by striking knobbly seedpods from which bright red seeds emerge in autumn.

Site and conditions

Site in full sun to give the best growth and flowering. Magnolias thrive in any fertile, moist garden soil that is not dry and alkaline:

  • For dry, alkaline soils consider Magnolia grandiflora and M. delavayi. On moist, alkaline soils try M. kobus, M. × loebneri, M. seiboldii, M. stellata and M. wilsonii. Magnolia grandiflora and M. virginiana will tolerate wet soils
  • Some later flowering deciduous species, such as M. wilsonii and M. sieboldii, will enjoy light dappled shade
  • A sheltered site is important. M. grandiflora and M. delavayi grow best on a warm wall and may not survive in regions where the temperature drops below -5°C (23°F). Frosts can damage flowers in spring and evergreen foliage in autumn
  • Magnolia grandiflora is not especially 'windfirm' and may need staking when planted in the open, even when quite mature
  • Magnolias, especially evergreen ones, are commonly grown against walls. Despite this, reports of damage to buildings by magnolias are uncommon
  • Plant as for other trees
  • Magnolias can be grown in containers

Pruning and training Back to top

Deciduous magnolias

Pruning is seldom required, with the following exceptions:

  • Shape trees at planting time by removing weak and badly placed growth and tipping back long shoots
  • Heavy pruning of mature magnolias can induce watershoots (long, vertical, vigorous shoots) and dieback. Routine pruning is therefore usually restricted to removing deadwood and watershoots
  • When pruning to limit size, aim to maintain an open, balanced crown by thinning out stems to the trunk or to a sideshoot. Stage the pruning over several years to avoid stressing the tree
  • Renovation should also be done over two or three years and trees can be slow to recover
  • Prune branches back to a natural fork to avoid leaving unsightly stubs
  • Cuts bleed if pruned in late winter or early spring so pruning should only be done between mid-summer and early autumn

Evergreen magnolias

  • Young trees need no pruning other than shortening of lengthy, young branches and removal of lower boughs, where a bare stem is desired
  • Hard pruning is tolerated when renovation or repair of storm damage is required. Cut back to the main framework or even beyond. However, it is safest to spread this work over several years
  • Otherwise, prune free-standing trees in spring, as growth begins and wall-trained specimens in summer

Wall-training

The evergreen Magnolia grandiflora flowers and grows particularly well if trained against a sunny wall;

  • Wall-trained trees are trained by tying to wires or other supports, initially tying in shoots at 45 degrees, then lowering them to the horizontal the following season
  • Regular pruning consists of removing shoots growing towards the wall, and shortening outward-growing ones to one or two leaves
  • If these outward-growing shoots bear flower buds, pruning can be delayed until immediately after flowering

Propagation Back to top

Layering shoots near ground level is the easiest propagation method.

Deciduous magnolias can be propagated from soft- and greenwood cuttings. Liquid feed rooted cuttings and overwinter in a frost-free place. Magnolias are not easy to strike from cuttings and artificial light may be needed from summer until leaf fall if they are to be developed enough to survive the first winter.

For evergreens, take semi-ripe cuttings in late summer and early autumn.

Magnolias grow readily from seed but may take over 10 years to begin flowering. Collect seeds when the cones begin to split. Many of the seeds do not fully develop due to lack of pollination. The shiny black seeds will be covered by an orange-red fleshy covering which should be cleaned away with water. Mix the cleaned seed with moist sand or vermiculite, then place in a polythene bag in the refrigerator for two to four months before sowing under cover. Dried seed is often unsuccessful. Pot on seedlings as soon as large enough to handle and grow on in containers for two or three years before planting them in the garden.

Cultivar Selection Back to top

Magnolia stellata AGM: shrub to 3m (10ft) x 4m (13ft). Abundant, star-shaped, many-petalled pure white or faintly blushed flowers from early to mid-spring.

M. 'Jane' (Kosar hybrid) AGM: shrub to 4m (13ft) x 3m (10ft). Cup-shaped, fragrant, purple-red flowers in late spring.

M. × loebneri 'Leonard Messel' AGM: rounded tree to 8m (24ft) x 6m (20ft). Many-petalled, star-shaped, pale pink flowers in mid-spring.

Links

RHS Plant Selector
RHS Plant Finder
RHS Trials and AGMs

Magnolia

Magnolia 'Jane' (Kosar hybrid) AGM

Problems Back to top

Non-flowering: Newly planted trees can take several years to settle before starting into flower. Flowering is very dependent on site, and for M. grandiflora plants in warm, sunny conditions are likely to flower best. Excess pruning can also delay flowering.

Blackened flowers or buds: Flowers and flower buds of the early spring flowering magnolias are susceptible to frost damage.

Yellow leaves: Young leaves of many magnolia are naturally pale but yellowing of more mature foliage may be caused by excessive alkalinity.

Leaf loss: Leaves of evergreen magnolias are long lasting but are shed after several years leading to harmless, if alarming, leaf fall episodes in early summer.

Watch out also for signs of bracket fungibrown leaves, honey fungus and Phytophthora root rot.

Quick facts

Common name Magnolia
Botanical name Magnolia
Group Shrub or tree
Flowering time Spring, summer
Planting time Autumn, winter and spring
Height and spread 2-15m (6½-50ft) by 3-10m (10-33ft)
Aspect Sun or part shade, sheltered
Hardiness Fully hardy but flower buds may be frosted
Difficulty Moderate

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