Illustration
Cascade Penstemon
Penstemon serrulatus
Also called coast penstemon, cascade beardtongue, serrulate beardtongue and serrulate penstemon
Also comes in blue.
Cascade Penstemon blooms from June through August.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Cascade Penstemon
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 6–9. Expect it to reach about 20 in tall and 20 in wide at maturity, in roughly 4 years (checked).
Pets
- Not yet checked for pets.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
No toxicity note is on file for Cascade Penstemon. That is not a clearance: check its safety for people and pets before planting.
What was checked
Nine facts were checked against named botanical sources, each recorded beside the sources that carried it: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. Soil, diseases, pests, toxicity and the plant's own names have not yet been read for this plant, and its trait tags are the ones a feature uses rather than every word a page prints. Each fact above carries its own mark. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Cascade Penstemon
Plant Cascade Penstemon in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 7, the middle of its hardy zones 6 to 9, spring means March to May and fall means September or October. Once settled, it blooms from June to August.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 7, the middle of this plant's hardy range, start with zone 7 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Cascade Penstemon get?
20 intall5 ft 7 inan adult20 inwideSee Cascade Penstemon in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Cascade Penstemon
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Cascade Penstemon about 20 in apart, center to center, so each plant has room to reach its full width.
Add Cascade Penstemon to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Cascade Penstemon's height, spread, hardiness zones, sun, water, bloom months and color, years to mature size and trait tags were checked against 8 published sources on November 5, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- dev.offthewallmedia.comSevenoaks Native Nurseryheight, spread, hardiness zones, sun, water and bloom months and color
- extension.oregonstate.eduOregon State University Extension Serviceheight, sun, water, bloom months and color and trait tags
- sparrowhawknativeplants.comSparrowhawk Native Plantsheight, spread, sun, water and bloom months and color
- wnps.orgWashington Native Plant Societyheight, sun, water, bloom months and color and trait tags
- green2.kingcounty.govKing County, Washington, Native Plant Guideheight, sun, water and bloom months and color
- RHSRoyal Horticultural Societyheight, sun, bloom months and color and years to mature size
- wolfelab.asc.ohio-state.eduThe Ohio State University, Wolfe Labheight, water, bloom months and color and trait tags
- burkeherbarium.orgUniversity of Washington, Burke Herbariumheight, bloom months and color and trait tags
How the checking works, and what each standard covers, is on the verified plants page.
Where it grows wild
Native to 3 states and 1 province
United States: Alaska, Oregon, Washington
Canada: British Columbia
Recorded growing wild in 33 counties.
Range data from the World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 4.0, adapted) and USDA PLANTS. How the native range is credited.
Explore similar plants
You might also like
Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.