Rock Elm
Ulmus thomasii
- Native to:
- Canada, United States
Douglas Goldman






Taxonomy
- Division:
- Magnoliophyta | - Flowering plants
- Family:
- Ulmaceae
- Genus:
- Ulmus
- Species:
- Ulmus thomasii
- USDA Symbol:
- ULTH
Growth Characteristics
- Life Cycle:
- Perennial
- Growth Habit:
- Tree
- Height:
- 2100 cm
- Light Requirements:
- Full Sun,Part Shade,Shade
- Drought Tolerance:
- Medium
- Bloom Months:
- mar,apr,may
- Bloom Colors:
- green
Wildlife Benefits
- Caterpillars:
- ★☆☆☆☆ Recorded caterpillar host plant (HOSTS Database)
Keystone Species Ranking
- Caterpillar Keystone:
- ★★★★★ Butterfly & moth species supported by this genus (NWF)
Host Plant for Caterpillars
Canadian Melanolophia (Melanolophia canadaria), Cecropia moth (Hyalophora cecropia), Imperial Moth (Eacles imperialis), Theisoa constrictella
Garden & Ecology Notes
- Wildlife Value:
- birds, small mammals
- Fall Color:
- yellow
Soil Requirements
- Soil Type:
- rich, well-drained loamy soil
- pH:
- 6.0 - 8.0 (slightly acidic to neutral)
- Drainage:
- tolerates moderate drainage
- Moisture:
- dry to moderate
- Notes:
- Prefers calcareous soils; often found on limestone outcrops
Propagation & Germination
- Stratification:
- Cold/moist stratification required — 60–90 days
- Germination Time:
- 14–28 days
- Notes:
- Seeds are short-lived and should be sown fresh. Cold stratification improves germination rates.
The above propagation data sourced from Claude AI
Pre-treatment: Cold-moist stratification for 30 days at 1–5°C (34–41°F).; then Cold-moist stratification for 60 days.
Source: Claude AI