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Rock Elm, Cork Elm

Ulmus thomasii

Family: Ulmaceae (ulm-AY-see-ee) (Info)
Genus: Ulmus (ULM-us) (Info)
Species: thomasii (to-MAS-ee-eye) (Info)



Foliage Color:

Unknown - Tell us

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Water Requirements:

Average Water Needs; Water regularly; do not overwater

Where to Grow:

Unknown - Tell us


over 40 ft. (12 m)


30-40 ft. (9-12 m)

over 40 ft. (12 m)


USDA Zone 3b: to -37.2 C (-35 F)

USDA Zone 4a: to -34.4 C (-30 F)

USDA Zone 4b: to -31.6 C (-25 F)

USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

Sun Exposure:

Full Sun

Sun to Partial Shade



Bloom Color:

Pale Green


Bloom Time:

Late Winter/Early Spring

Mid Spring




Good Fall Color

Other details:

Unknown - Tell us

Soil pH requirements:

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

Patent Information:


Propagation Methods:

From softwood cuttings

From semi-hardwood cuttings

From seed; direct sow outdoors in fall

Seed Collecting:

Allow seedheads to dry on plants; remove and collect seeds


This plant has been said to grow in the following regions:

Champaign, Illinois

Lisle, Illinois

Gardeners' Notes:


On Jun 25, 2015, Rickwebb from Downingtown, PA wrote:

It is a species similar to the American or White Elm, but not really vase-shaped in form. The leaves are a little smaller than the American's, being 2.5 to 4.5" long x 1.5 to 2.5" wide. (American Elm's leaves get to 6" long x 3" wide). The foliage seems a little darker and of a thicker texture. The twigs and stems are usually rather corky, but there is variation with less corkiness. It is also called Cork Elm. It is native to southern Ontario, NY to southern MN and northern WI down to TN. I've only seen two specimens in the Elm Collection of Morton Arboretum in Lisle, Illinois. Dutch Elm Disease and Elm Yellows Disease, both from East Asia, have lessened the populations of this species as with other native elm species. If I have ever seen them in the wild, I have not recognized them, mayb... read more


On May 20, 2011, srhill from Champaign, IL wrote:

My experience is that the seeds must be planted immediately while still green and fresh, in the Spring. They seem to be killed by drying. Extremely slow growing elm. Becoming rare - needs more propagation !


On Apr 8, 2005, melody from Benton, KY (Zone 7a) wrote:

Information only, I do not grow this plant.

This tree has a wonderful straight trunk and is a valuable hardwood. It is found in moist to dry uplands, rocky ridges and limestone bluffs.

It's range is from S. Ontario and S. Quebec, through New England south to TN and West to KS.

The very hard wood is difficult to split, making it valuable for tool handles. In the 19th century, the wood was exported to England for the construction of wooden battleships and sailing vessels.