glaucus willowherb
Epilobium glaberrimum · Onagraceae
glaucus willowherb (Epilobium glaberrimum) is a perennial herbaceous plant in the Onagraceae family. It is native to North America. USDA records it as hardy in zone 6 and warmer, down to about -8°F.
At a glance
| Type | forb-herb USDA |
|---|---|
| Lifecycle | perennial USDA |
| Native status | native USDA |
| Mature height | 2 ft USDA |
| Light | shade USDA |
| Water need | medium USDA |
| Growth rate | slow USDA |
| Soil pH | 6.1–7.5 USDA |
| Bloom | July USDA |
| Flower color | Purple USDA |
| Hardiness zones | 6 and warmer USDA |
| Guild layer | herb-layer 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 tolerates full shade. USDA rates it as having moderate water needs. 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 6.1 to 7.5 — a broad range that spans acidic through mildly alkaline ground. Its cold limit is zone 6.
Size and growth
At maturity it reaches about 2 ft, making it about knee height. It grows slowly.
Bloom period
USDA records a bloom period of July. Flowers are purple.
A flowering date, not a pollinator rating.
Foliage, flower and season
Summer foliage is dark green, medium 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 moderate.
What the site needs to provide
USDA records it across sites receiving 12 to 20 inches of annual precipitation. The low end of that band is genuinely arid, so it has a wide tolerance for dry country. It needs at least 200 frost-free days to finish its season. It roots to at least 8 inches. Fertility requirement: low — no feeding needed on ordinary garden soil.
Propagating it
Seed is the only propagation method USDA lists. Division and cuttings are not listed as options. USDA records no cold-stratification requirement, so seed should germinate without a chilling period. Its seed spreads at a moderate rate. It spreads vegetatively at a slow rate.
Resilience and wildlife
Browsing animals rate it barely palatable — the sourced basis for calling it deer-resistant. Its fire tolerance is rated high. Its growth form is recorded as rhizomatous.
Role in a guild
Herb layer. In a layered planting this is the herbaceous middle — perennials and grasses that fill the space between ground cover and shrubs. The layer is derived by a fixed rule from growth habit and mature height.
Tags
Related plants
Others in Epilobium
- purpleleaf willowherb Epilobium coloratum
- bog willowherb Epilobium leptophyllum
Similar role and hardiness
- Rhodes grass Chloris gayana
- lanceleaf tickseed Coreopsis lanceolata
- tenangle pipewort Eriocaulon decangulare
- Atlantic mannagrass Glyceria obtusa
- Palmer's penstemon Penstemon palmeri
Where this data comes from
Every value on this page comes from the USDA PLANTS database record for symbol EPGL, 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, Edible, 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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