Cold hardiness

Future

2050

2100

These values are location-based: this location's current hardiness is the baseline, and the 2050 value is a projected future climate for this same location.

Now

Zone 6b

USDA

Published baseline for this location from 1991-2020.

Source: USDA Plant Hardiness Zone Map 2023 (1991-2020 climatology) via ArcGIS FeatureServer

Well-suited

2050

Zone 7a

Plotwright

Projected zone for this same location in 2050 (2041-2070) using SSP3-7.0 (regional rivalry).

Well-suited

In plain terms: This location is in Zone 6b today. Its hardiness profile is cold winters, and coldest nights are typically around -3°F. By 2050, the projected hardiness zone is Zone 7a based on SSP3-7.0 (regional rivalry). That is a +0.5-zone shift from Zone 6b to Zone 7a by 2050.

✓

Well-suited today and still thriving in 2050.

Heat tolerance

Future

2050

2100

Heat tolerance values are location-based too: heat days today are observed at this site, and the 2050 value projects this same location under a future climate.

Loading AHS heat-zone data for this location...

Where this plant fits

Suitable across 41 ecoregions — 40 climate-resilient through 2070 · 1 suited today. Best matches first.

Appalachian mixed mesophytic forests

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Appalachian-Blue Ridge forests

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Arizona Mountains forests

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Atlantic coastal pine barrens

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Blue Mountains forests

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Canadian Aspen forests and parklands

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Central Pacific Northwest coastal forests

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Central Tallgrass prairie

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Central-Southern Cascades Forests

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Chilean Matorral

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What it needs

Conditions

Light

Full sun / Part sun / Part shade

Water

Moderate water

Spacing

72"

Habit

Multi-stemmed dense rounded evergreen shrub

Care tips

•

Acidic + humus-rich + cool-moist + well-drained soil are all load-bearing — mountain laurel fails predictably in alkaline, hot-dry, or chronically wet sites. Test soil pH before planting.

•

Mulch generously with pine straw or oak leaf litter — mountain laurel requires acidic mulch chemistry + cool root-zone temperatures.

•

Site in dappled shade with good air movement to minimize lace bug pressure; sun-stressed plantings in hot dry sites are the canonical lace-bug-dominant failures.

Lifecycle

Planting

Plant in spring or fall in acidic, humus-rich, cool moist well-drained soil — these are load-bearing conditions, not preferences. NC State explicitly notes mountain laurel prefers partial shade with morning sun + early-afternoon shade; tolerates full sun in cool moist sites and full shade with reduced bloom. Avoid heavy clay + chronically wet sites (root rot risk).

Transplanting

Transplant at small-to-medium container sizes (3-7 gallon); larger balled-and-burlapped stock requires careful aftercare. Best moved in early spring before bud break.

Early growth

Water through dry spells, especially during the first 2-3 establishment seasons. Mulch generously with pine straw or oak leaf litter to maintain acidic soil chemistry + cool roots. NC State emphasizes the species needs mulch.

Maturity

Mature plants reach 4-15 feet tall and 4-8 feet wide. Very long-lived (50-100+ years in undisturbed acid woodland sites). Flowers form on the previous year's growth — prune lightly after bloom if shaping is wanted; heavy pruning sacrifices the next year's bloom.

Propagation

Difficult from cuttings; usually propagated by seed in commercial production (slow + variable) or by layering. Named cultivars ('Sarah', 'Olympic Fire', 'Carousel', 'Tad') are vegetatively propagated and offer expanded color range from the wild pink/white.

Pollination

Self-fertile

NC State documents an unusual spring-loaded pollination mechanism: "10 anthers on recurved filaments held under tension in the corolla. When triggered by visiting pollinators, the filaments spring toward the center, striking the pollinators with pollen." Bumblebees + other large native bees are the primary effective pollinators; honeybees also visit but the species's mechanism evolved for native bumblebee-sized visitors.

Plants don't grow alone

Pollinates

Bee

Common eastern bumblebee (Bombus impatiens)

NC State documents bumblebees as primary pollinators via the spring-loaded anther-trigger mechanism. The flower's unique architecture co-evolved with native bumblebee-sized visitors — honeybees pollinate less efficiently because they're smaller than the trigger mechanism's target.

Nectar forage

Bird

Ruby-throated hummingbird (Archilochus colubris)

NC State explicitly names hummingbirds among visitors; the cup-shaped flowers hold nectar that hummingbird tongues can access despite the species's primary bumblebee co-evolution.

Nectar forage

Butterfly

Eastern tiger swallowtail (Papilio glaucus)

For people

Toxic — do not consume

NC State explicitly flags mountain laurel as HIGH-SEVERITY poisonous. ALL plant parts (bark, flowers, fruits, leaves, roots, seeds, stems) contain grayanotoxins (also called andromedotoxins) that cause severe gastrointestinal + cardiovascular symptoms in humans, dogs, cats, horses, and livestock. CRITICAL: honeybees that forage heavily on Kalmia produce "mad honey" — a regional phenomenon in parts of the southeast US + Mediterranean Turkey where Ericaceae-dominated landscapes lead to grayanotoxin-contaminated commercial honey. Do not consume any plant part. Wash hands after pruning.

Native range

Native across 25 US states + 1 CA province.

AHS heat range

1-11

Native ecoregions

Naturally belongs in 13 ecoregions — its native range crosses a state or province each one spans (not necessarily this exact habitat).

Appalachian mixed mesophytic forests

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Appalachian-Blue Ridge forests

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Atlantic coastal pine barrens

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Eastern Canadian Forest-Boreal transition

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Eastern Great Lakes lowland forests

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Mississippi lowland forests

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Northeastern Coastal Forests

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Northeastern Hardwoods

Climate notes

•

NC State Extension lists Kalmia latifolia for USDA hardiness zones 4a-9b across the eastern United States from New England south to the southern Indiana, Louisiana, and Florida panhandle.

•

Acid-soil specialist (Ericaceae family); fails in alkaline soils. Tolerates rocky / sandy / acidic woodland margins; intolerant of heavy clay + chronically wet sites (Phytophthora root rot).

•

Pest pressure per NC State: borers, scale, whitefly, lace bugs (lace bugs are the most chronic + recognizable in sun-stressed plantings). Disease: leaf spots, leaf blights. Site in dappled shade with good air movement to minimize pressure.

In the designer

Growth over time

48-180" tall · 48-96" spread

Mature dense evergreen shrub; very long-lived (50-100+ years).

Design roles: Structure · Pollinator · Focal point

Seasonal interest

Spring

Summer

Fall

Winter

Filled = the plant has seasonal interest · ▾ now = your current season

Mountain laurel

At a glance

Related products

Why it matters

Cold hardiness

Heat tolerance

Where this plant fits

What it needs

Lifecycle

Pollination

Plants don't grow alone

For people

Native range

Climate notes

In the designer

Seasonal interest

Sources & citations