Ulmus thomasii

Common Names

Rock Elm, Cork Elm

Summary

Rock elm is a deciduous tree native to eastern and central North America that typically grows 50–100 ft tall with a broad, cylindrical to oblong crown and a trunk up to about 3 ft in diameter. It features corky wings on older branches, elliptical to oblong leaves with doubly serrate margins, and deeply furrowed bark; the wood is extremely hard and heavy with a close grain, valued for furniture, general construction, agricultural implements, wheel hubs, and shipbuilding.

In cultivation, it prefers full sun to partial shade and well-drained soils (pH 6.0–7.5), is hardy in USDA zones 3–7, and is best planted in early spring or late fall with the root flare at ground level; mulch 2–3 inches, deep watering and allowing the top inch to dry between waterings, pruning during dormancy, and slow-release balanced fertilizer as needed. It propagates by seed, with germination in 1–2 weeks, and can regrow vegetatively by root suckers and stump sprouts; it is moderately shade-tolerant as a seedling, but older trees require more light, and it is very susceptible to Dutch elm disease.

Lifecycle

Perennial

Height

50-100 feet

Spread

70-90 feet

Hardiness Zones

Zones 3-7

Sunlight Requirements

Ideally full sun. Also acceptable: partial sun, partial shade, full shade.

Soil Type

Moist, well-drained loamy soil (sandy loam, loam, or silt loam), pH 6.0–7.5.

Soil Drainage

Moist but well-drained soil

Soil pH

Soil pH range: slightly alkaline or neutral to strongly acidic.

Bloom Color

Red-green

Bloom Time

Spring (March-May)

Foliage Color

Dark green foliage with a shiny upper surface and paler lower surface; autumn foliage bright yellow.

Fall Foliage Color

Bright yellow

Leaf Lifecycle

Deciduous

Growth Rate

Very slow growth; up to 2 mm/year

Seasons of Interest

Spring and Fall

Propagation Methods

Seeds, Cuttings, Division, Layering

Attracts Wildlife

Wind-pollinated; no evidence of attraction to bees, hummingbirds, butterflies, other pollinators, or birds.