Magnolia grandiflora'Glen St. Mary': 'Glen St. Mary' Southern Magnolia1
This cultivar of the native Southern Magnolia flowers at a very early age. Trees three-years-old in three gallon containers often bear a number of flowers. The species has been selected as the state tree of Mississippi. Growing at a slow rate to a height of probably 25 feet with a 10 to 12 foot spread, it forms a dense, dark green pyramidal or tight oval shape. Lower branches often remain on the tree but grow upright, not bending to the ground as the species does.
Scientific name: Magnolia grandiflora
Pronunciation: mag-NO-lee-uh gran-dih-FLOR-uh
Common name(s): 'Glen St. Mary' Southern Magnolia
USDA hardiness zones: 7A through 10A (Fig. 2)
Origin: native to North America
Invasive potential: little invasive potential
Uses: container or planter; street without sidewalk; deck or patio; screen; specimen; espalier; tree lawn 3-4 feet wide; tree lawn 4-6 feet wide; tree lawn > 6 ft wide
Availability: somewhat available, may have to go out of the region to find the tree
Height: 20 to 25 feet
Spread: 15 to 20 feet
Crown uniformity: symmetrical
Crown shape: pyramidal, oval
Crown density: dense
Growth rate: slow
Leaf arrangement: alternate (Fig. 3)
Leaf type: simple
Leaf margin: entire
Leaf shape: elliptic (oval), ovate
Leaf venation: brachidodrome, pinnate
Leaf type and persistence: evergreen, broadleaf evergreen
Leaf blade length: 4 to 8 inches, 8 to 12 inches
Leaf color: green
Fall color: no color change
Fall characteristic: not showy
Flower color: white/cream/gray
Flower characteristics: very showy
Fruit shape: elongated
Fruit length: 1 to 3 inches, 3 to 6 inches
Fruit covering: dry or hard
Fruit color: brown, red
Fruit characteristics: attracts birds; showy; fruit/leaves a litter problem
Trunk and Branches
Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns
Pruning requirement: little required
Current year twig color: green
Current year twig thickness: thick
Wood specific gravity: 0.50
Light requirement: full sun, partial sun or partial shade
Soil tolerances: sand; loam; clay; acidic; slightly alkaline; well-drained; occasionally wet
Drought tolerance: moderate
Aerosol salt tolerance: moderate
Roots: not a problem
Winter interest: no
Outstanding tree: yes
Ozone sensitivity: unknown
Verticillium wilt susceptibility: susceptible
Pest resistance: resistant to pests/diseases
Use and Management
The five to 8-inch-long, leathery, oblong, shiny leaves are shed as new leaves emerge but the debris is well-hidden by the dense foliage of the lower limbs, if they are left on the tree. But some people consider this a litter nuisance when the large, slowly-decomposing leaves drop on the sidewalk, lawn, or patio. The underside of the leaves is covered with a fine, red-brown fuzz which is more prominent than on the species but not as nice as `Bracken's Brown Beauty'. In late spring and sporadically throughout the summer, huge, 8-inch-diameter, waxy, fragrant, white blossoms open to perfume the entire garden. Fuzzy brown cones follow these blooms, ripening in fall and winter to reveal bright red seeds which are used by a variety of wildlife.
Suitable as a striking garden specimen, Southern Magnolia can also serve as a dense screen or windbreak. Winter winds may dry out the foliage in the northern part of its range if exposed to direct wind. Its ease of growth and carefree nature make Southern Magnolia ideal for the low-maintenance landscape. With proper pruning, Southern Magnolia trees can also be used as an interesting espalier.
If moist, peaty soils are available, Southern Magnolia will thrive in full sun and hot conditions once established. If irrigation cannot be provided periodically, plants located in partial shade for several years after planting seem to grow better. Very drought tolerant when grown in areas with plenty of soil for root expansion. Only moderately drought tolerant in restricted-soil areas or in areas with poor, dry soil. Southern Magnolia prefers acid soil but will tolerate a slightly basic, even wet or clay soil. It is generally too hot and dry in central and western Texas and Oklahoma, and the soil pH is often too alkaline for this tree.
The root system on the species is wider spreading than most other trees, extending from the trunk a distance equal to about four times the canopy width. This makes it very difficult to save existing Magnolia trees on construction sites.
Be sure that there are no roots circling close to the trunk, as Magnolia is prone to girdling roots. Cut any circling roots prior to planting. Field-grown trees recover slowly from transplanting due to the wide-spreading root system in the nursery, and trees often transplant best in winter and spring, not in the fall. This and the other small cultivars may transplant with less shock and less leaf loose than the species.
The species germinated from seed is quite variable in growth rate and form with some trees dense and compact, others loose and open. A number of other cultivars are available: `Bracken's Brown Beauty' has an unusually dark brown lower leaf surface; `Cairo' has an early and long flowering period; `Charles Dickens' has broad, nearly blunt leaves, large flowers and large red fruit; `Edith Bogue' is the hardiest of the cultivars and will bloom when only two to three-years-old; `Gloriosa' has large flowers and leaves; `Goliath' has flowers up to 12 inches across, a long blooming period, and a bushy habit of growth; `Hasse' can be used for a compact, dense hedge or screen; `Lanceolata' has a narrow pyramidal form, narrower leaves with rusty undersides; `Little Gem' has a dwarf upright form, probably to 30 feet tall, small leaves and flowers, is very slow-growing, flowers heavily at an early age and for a long time during the summer (5-months), and has bronze leaf-undersides. It will bloom when only three to four feet tall and is excellent as a pruned evergreen hedge, for use as a small street tree or for use as an espalier. `Majestic Beauty' (patented) has large, dark green leaves, a pyramidal shape, and profuse flowering; `Praecox Fastigiata' has upright, narrow growth habit; `Samuel Sommer' has an upright, rapid growth habit and flowers up to 14 inches across; `Victoria' is very hardy, has small flowers, and rust-red leaf-undersides. There are others, often difficult to see real differences among a number of cultivars.
Two of the most recommended Magnolias are: Magnolia x `Galaxy' and `Spectrum' from U.S. National Arboretum; both have excellent trunks and superior flowers.
Propagation is by cuttings (for the cultivars), grafting, or seed.
Scales of various types will infest twigs and leaves. Magnolia scale is the most common scale and can be one half-inch-across. Overwintering scales can be controlled with horticultural oil. Trees appear to grow fine even with heavy infestations, although they can be unsightly.
Tulip-poplar weevil (sassafras weevil) feeds as a leaf miner when young and chews holes in the leaves as an adult.
Magnolia borer is a problem on young nursery stock. It girdles the trunk usually just below the soil surface. Control is difficult but attainable with the proper material.
Magnolia may be subject to leaf spots, blights, scabs and black mildews caused by a large number of fungi, or a bacterium but they rarely require chemical controls. Raking up and disposing infected leaves may reduce leaf spots next year. Algae can also cause leaf spots.
Canker diseases will kill branches. Cankers on branches can be pruned out. Keep trees healthy with regular fertilization and by watering in dry weather.
Verticillium wilt may cause death of a few branches or, rarely, may kill the tree. Prune out dead branches and fertilize.