Illustration
Obsidian
Heuchera 'Obsidian'
Obsidian is grown for its foliage rather than flowers, giving the garden structure and color all season long.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Obsidian
Plant it in part shade. It prefers moderate water. It is hardy in USDA zones 4–9. Expect it to reach about 14 in tall and 16 in wide at maturity, in roughly 2 years (not yet checked).
No toxicity note is on file for Obsidian. That is not a clearance: check its safety for people and pets before planting.
What was checked
Mature height and spread, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not, and each fact above says which. 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 Obsidian
Plant Obsidian 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 6, the middle of its hardy zones 4 to 9, spring means March to May and fall means August or September.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Obsidian get?
14 intall5 ft 7 inan adult16 inwideSee Obsidian 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 Obsidian
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Obsidian about 16 in apart, center to center, so each plant has room to reach its full width.
Add Obsidian 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
Obsidian's height, spread, hardiness zones, sun and trait tags were checked against 10 published sources on July 30, 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.
- Perennial Resource (Walters Gardens)height, spread, hardiness zones, sun, years to mature size and trait tags
- plants.platthillnursery.comPlatt Hill Nursery (NetPS Plant Finder)height, spread, hardiness zones, sun, years to mature size and trait tags
- terranovanurseries.comTERRA NOVA Nurseries (breeder and introducer)height, spread, hardiness zones, sun, years to mature size and trait tags
- Perennials.com (Heritage Perennials)Heritage Perennials (perennials.com)height, spread, hardiness zones, sun and years to mature size
- US plant patent (Google Patents)Heuchera plant named 'Obsidian'height, spread, hardiness zones, years to mature size and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones and sun
- NC State ExtensionPlant Toolboxhardiness zones, sun, years to mature size and trait tags
- Pleasant Run Nurseryheight, spread, hardiness zones and sun
- NC State ExtensionPlant Toolboxhardiness zones, sun and trait tags
- RHSRoyal Horticultural Societyheight and spread
How the checking works, and what each standard covers, is on the verified plants page.
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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.