rock elm
Ulmus thomasii · Ulmaceae
rock elm (Ulmus thomasii) is a perennial tree in the Ulmaceae family. It is native to North America. USDA records it as hardy in zone 2 and warmer, down to about -46°F.
At a glance
| Type | tree USDA |
|---|---|
| Lifecycle | perennial USDA |
| Native status | native USDA |
| Mature height | 90 ft USDA |
| Light | part-shade USDA |
| Water need | high USDA |
| Growth rate | moderate USDA |
| Soil pH | 4.5–7.2 USDA |
| Bloom | April–May USDA |
| Flower color | Yellow USDA |
| Hardiness zones | 2 and warmer USDA |
| Guild layer | canopy Derived |
| Nursery availability | No Known Source USDA |
USDA quoted from the USDA PLANTS database · Derived computed by a fixed rule from those columns. No value on this page is estimated.
Growing conditions
It grows in partial shade. USDA rates it as having needs consistently moist ground. Its drought tolerance is rated low. It will not tolerate waterlogged soil — USDA rates its anaerobic tolerance as none. It is recorded on soils from pH 4.5 to 7.2 — a broad range that spans acidic through mildly alkaline ground. Its cold limit is zone 2.
Size and growth
At maturity it reaches about 90 ft, making it a large tree that will dominate its site. It grows at a moderate rate.
Bloom period
USDA records a bloom period of April through May. Flowers are yellow.
A flowering date, not a pollinator rating.
Foliage, flower and season
Summer foliage is green, coarse in texture. Its flowers are not conspicuous — a plant for form and foliage. Its active growth period is spring and summer. USDA rates its lifespan as long.
What the site needs to provide
USDA records it across sites receiving 22 to 60 inches of annual precipitation. It needs at least 120 frost-free days to finish its season. It roots to at least 40 inches, too deep for containers or thin soil over bedrock. Fertility requirement: medium.
Propagating it
It takes readily from seed, cuttings, bare root and container stock. USDA records no cold-stratification requirement, so seed should germinate without a chilling period. Its seed spreads at a slow rate. It does not spread vegetatively, so it will stay where you put it.
Resilience and wildlife
Browsing animals rate it barely palatable — the sourced basis for calling it deer-resistant. Its fire tolerance is rated medium, and it can resprout after damage. Its growth form is recorded as single stem.
Role in a guild
Canopy. In a layered planting this is the tallest layer of a planting — it sets the light budget everything beneath it lives on. The layer is derived by a fixed rule from growth habit and mature height.
Tags
Related plants
Others in Ulmus
- winged elm Ulmus alata
- American elm Ulmus americana
- cedar elm Ulmus crassifolia
- Chinese elm Ulmus parvifolia
Similar role and hardiness
- boxelder Acer negundo
- red maple Acer rubrum
- silver maple Acer saccharinum
- sugar maple Acer saccharum
- bitternut hickory Carya cordiformis
Where this data comes from
Every value on this page comes from the USDA PLANTS database record for symbol ULTH, or is computed from those values by a fixed rule. Nothing here is estimated or model-generated. Where USDA publishes no value, this page omits the claim rather than filling the gap.
- Quoted from USDA PLANTS: active growth period, Bloom, Bloom end, browse palatability, cold stratification, Drought tolerance, fall conspicuous, fertility requirement, fire tolerance, Flower color, flower conspicuous, foliage color, foliage porosity winter, foliage texture, frost free days min, fruit conspicuous, growth form, Growth rate, Hardiness zones, Lifecycle, lifespan, Light, Mature height, Minimum temperature, Native status, Nitrogen fixation, Nursery availability, precipitation max in, precipitation min in, propagation, resprout ability, root depth in, seed spread rate, Soil pH, Soil pH (upper), Tolerance of wet soil, Toxicity, Type, vegetative spread rate, Water need.
- Derived by a fixed rule from those columns: Guild layer.
Read our full data sources and methodology.
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