• Topics: Blackgum | Southern Trees Fact Sheets | Nyssaceae (taxonomic family)

Nyssa sylvatica: Blackgum¹

Introduction

Sourgum is a hardwood tree which grows to 75 feet tall, has a medium growth rate, pyramidal shape with horizontal branches growing from a typically straight trunk. But the shape of the crown varies from tree to tree and, unfortunately, this is looked upon by some architects as undesirable. As the tree grows to 10 and 15-years-old, crown form becomes more uniform among trees. Lower branches droop with age and will need to be removed if used as a street tree. Growth habit is similar to pin oak, a tree which many people are familiar with. Providing a brilliant display of red to deep purple foliage in the fall, Sourgum surprises most people since it does not particularly stand out in the landscape until then. The small, blue fruits may be considered a litter nuisance in urban/suburban plantings but are quite popular with many birds and mammals, and they wash away quickly.

Figure 1. 

Young Nyssa sylvatica: Blackgum

[Click thumbnail to enlarge.]

General Information

Scientific name: Nyssa sylvatica

Pronunciation: NISS-uh sill-VAT-ih-kuh

Common name(s): Blackgum, Sourgum, Black Tupelo

Family: Nyssaceae

USDA hardiness zones: 4B through 9B (Fig. 2)

Origin: native to North America

Invasive potential: little invasive potential

Uses: reclamation; specimen; street without sidewalk; shade; parking lot island 100-200 sq ft; parking lot island > 200 sq ft; sidewalk cutout (tree pit); tree lawn 4-6 feet wide; tree lawn > 6 ft wide; highway median

Availability: somewhat available, may have to go out of the region to find the tree

Figure 2. 

Range

[Click thumbnail to enlarge.]

Description

Height: 65 to 75 feet

Spread: 25 to 35 feet

Crown uniformity: symmetrical

Crown shape: pyramidal, oval

Crown density: moderate

Growth rate: slow

Texture: medium

Foliage

Leaf arrangement: alternate (Fig. 3)

Leaf type: simple

Leaf margin: entire

Leaf shape: elliptic (oval), oblong

Leaf venation: pinnate

Leaf type and persistence: deciduous

Leaf blade length: 2 to 4 inches, 4 to 8 inches

Leaf color: green

Fall color: orange, red

Fall characteristic: showy

Flower

Flower color: white/cream/gray

Flower characteristics: not showy

Fruit

Fruit shape: oval, round

Fruit length: less than .5 inch

Fruit covering: fleshy

Fruit color: blue

Fruit characteristics: attracts birds; not showy; fruit/leaves a litter problem

Trunk and Branches

Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns

Pruning requirement: little required

Breakage: resistant

Current year twig color: gray, brown

Current year twig thickness: thin, medium

Wood specific gravity: 0.50

Culture

Light requirement: full sun, partial sun or partial shade

Soil tolerances: clay; sand; loam; acidic; extended flooding; well-drained

Drought tolerance: high

Aerosol salt tolerance: moderate

Other

Roots: not a problem

Winter interest: yes

Outstanding tree: yes

Ozone sensitivity: tolerant

Verticillium wilt susceptibility: susceptible

Pest resistance: free of serious pests and diseases

Figure 3. 

Foliage

[Click thumbnail to enlarge.]

Use and Management

Sourgum prefers a moist, slightly acid soil. Larger specimens may be difficult to transplant from deep, well-drained field soil because of its deep roots and should only be transplanted from the field in the spring. Therefore, it is usually seen growing in containers at the nursery. Little pruning is required to form a well-structured tree since the trunk stays straight and branches usually grow at wide angles with the trunk. Sourgum makes a good street or parking lot tree for suburban neighborhoods, possibly for downtown areas. It should be used more often for this purpose but will benefit from occasional irrigation in droughts. Does amazingly well in wet, compacted soils typical of many urban areas with highly disturbed clay soil. It is also somewhat salt-tolerant for planting along the shore.

Sourgum is rarely attacked by pests, and when it is they are rarely serious enough to warrant control.

Nyssa sylvatica var. sylvatica grows on moist sites; var. aquatica has a buttressed and swollen trunk base and grows in swamps. Nyssa bicolor is very similar and often confused with Nyssa sylvatica .

Pests

Scales, including Sourgum scale, can be controlled with horticultural oil.

Forest tent caterpillar can defoliate the tree in the spring. Unless defoliation is extensive in two or more successive years, control is not needed.

Diseases

Several fungi cause cankers on Sourgum. As the cankers enlarge the infected stems die back. Trunk cankers cause tree dieback. Prune out infected branches and keep trees healthy.

Leaf spots cause purplish blotches on the upper leaf surface. Rake up and destroy infected leaves in the fall to reduce the disease potential for the following year, if you wish.

Recently a large number of trees have been discovered dying in the mountains of North Carolina, Tennessee, Virginia, and Georgia. The causal agent is unknown but symptoms include leaf spots, branch cankers, leaves dying and hanging on the tree, and leaf blotches.

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.

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