Rock Elm (Ulmus thomasii)

Rock Elm

Ulmus thomasii

Its furrowed bark and ascending branches carry quiet woodland strength. Deciduous hardwood tree; common name: cork elm.

Full sun
1–2/week
Moderate
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Plant Needs

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Sunlight Full sun to partial shade; mature trees tolerate moderate woodland shade
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Watering Water deeply during prolonged dry spells; established trees have moderate drought tolerance
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Temperature Extremely cold hardy; adapts to temperate continental climates
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Characteristics

  • Leaf: Oval to oblong, double-toothed margins, dark green upper surface, paler lower surface with fine hairs
  • Bark: Mature bark is deeply furrowed; young branches have corky, wing-like ridges
  • Flower: Small, greenish apetalous flowers in dense clusters
  • Fruit: Flat, winged samaras that mature in late spring
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Care Guide

Watering

Water young trees weekly during dry periods; established trees need supplemental water only in severe drought

Fertilization

Apply balanced slow-release fertilizer once in early spring. Avoid high-nitrogen fertilizers that may promote weak, disease-prone growth

Composted eggshell powder:Mix 1 tablespoon of finely ground, composted eggshell powder into the top 5 cm of soil annually in early spring; avoid overapplication to prevent soil alkalinity
Pruning
  • Prune dead, damaged, or crossing branches in late winter to early spring before new growth emerges
  • Thin crowded interior branches to improve airflow and reduce disease risk
  • Remove suckers at the base to maintain a single, dominant trunk form
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Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA: Non-toxic to cats

Humans: No documented toxic effects for humans

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Garden Uses & Culture

Culture: N/A

Usage: Hardwood for furniture, flooring, and tool handles; ornamental shade tree for urban parks