// SPECIES PROFILE · PERENNIAL · NATIVE · POLLINATOR · CLAY-TOLERANT

Foxglove Beardtongue

Penstemon digitalis

Foxglove Beardtongue is the stalwart white-flowered penstemon of eastern and central North America — a robust, long-lived perennial that sends up 2–4 ft stalks of pure white, tubular, foxglove- like flowers in late spring and early summer. It is one of the most garden-adaptable of all native penstemons, thriving in heavy clay, tolerating wet feet better than its western cousins, and self-sowing into a long-lived colony. The flowers are magnets for bumblebees, mining bees, and the occasional ruby-throated hummingbird, and the glossy, dark green to purple-tinged basal rosettes provide semi-evergreen structure through winter. For NE Oklahoma gardens, Penstemon digitalis is a top choice for sunny borders, cottage-planting drifts, and the ecologically minded mailbox strip.

// QUICK FACTS

Family: Plantaginaceae (plantain family); formerly Scrophulariaceae
Life cycle: Herbaceous perennial; semi-evergreen basal rosette
Native range: Eastern & central N. America — Maine to Minnesota, south to Texas and Georgia
USDA hardiness: Zones 3–8 (Tulsa = 7a/7b; may struggle in zone 8+ heat)
Mature size: Basal rosette 6–12 in tall × 12–18 in wide; flower stalks 2–4 ft
Bloom period: May – June (NE OK); 3–4 weeks
Flower: White, tubular, 1–1.5 in long; five lobes; sterile fifth stamen (beardtongue) with golden hairs
Sun: Full sun to part sun; blooms best in full sun
Soil: Adaptable: clay, loam, sandy loam; pH 5.5–7.5; tolerates moist to somewhat dry
Water: Medium; more moisture-tolerant than most penstemons
Wildlife: Bumblebee specialist · mining bee pollinator · hummingbird nectar · occasional host for checkerspot butterflies

Foxglove Beardtongue (Penstemon digitalis) with tall panicles of white tubular flowers — *Penstemon digitalis* — the elegant panicles of white tubular flowers with a faint pink blush at the throat. Photo: Rooted Revival.

Identification

[ field key — rosette · leaf · flower stalk · flower · fruit ]

Habit & Rosette

A clump-forming perennial with a basal rosette of glossy, semi-evergreen leaves that persists through winter, often turning burgundy-purple in cold weather. In spring, the plant sends up 1–4 erect, sturdy flowering stems (scapes) 2–4 ft tall, topped with panicles of white flowers. The stems are round, smooth, and often reddish-purple near the base. The overall form is upright and statuesque, similar in silhouette to a foxglove (Digitalis) — hence the common name — but Penstemon is unrelated and native to North America. The plant slowly expands by offsets; seedlings appear nearby in subsequent years.

Leaves

Basal leaves are spatulate to broadly lanceolate, 2–6 in long and 1–3 in wide, with entire to finely toothed margins, on short petioles. The upper surface is glossy dark green and smooth; the underside is paler. Stem leaves are opposite, smaller, sessile, and clasp the stem at the base, becoming progressively more lanceolate up the stem. A key identification feature: the stem leaves are not connate (fused) around the stem, unlike some other eastern penstemons. The glossy, almost rubbery leaf texture is distinctive.

Flowers

The inflorescence is an open terminal panicle with multiple branches, each bearing clusters of nodding, tubular flowers. Individual flowers are white, 1–1.5 in long, with a five-lobed corolla: two upper lobes and three lower lobes that flare outward. The throat is often marked with faint purple or pink nectar guides. Inside the flower tube lies the signature feature of the genus: a sterile fifth stamen (the staminode, or "beardtongue") that is densely covered with golden-yellow hairs at the tip. When a bumblebee enters the tube, these hairs brush against its back, aiding pollen transfer. Bloom lasts 3–4 weeks in May and June.

Fruit & Seed

After pollination, each flower develops a small, pointed capsule that dries and splits open to release numerous tiny, angular, dark brown seeds. The seed capsules persist on the dried stalks through summer and into fall, creating a subtle rattling sound in the wind. For the gardener who enjoys winter structure, the dried seed stalks are quite handsome if left standing. Seeds are easily collected by bagging the ripening capsules before they split. Each plant produces thousands of seeds, and self-sown seedlings are common in nearby bare soil.

Habitat & Range in NE Oklahoma

Penstemon digitalis is native across the eastern half of North America, from Maine and southern Ontario west to Minnesota and eastern South Dakota, and south to eastern Texas, Louisiana, and Georgia. In NE Oklahoma it is a widespread species of open woods, prairie margins, roadsides, and old fields, often on heavy clay or clay-loam soils in full to partial sun. It is particularly common along the edges of the Cross Timbers post oak-blackjack oak woodlands, where it grows at the transition between prairie opening and woodland shade, and along the unmowed margins of rural highways. It also colonizes disturbed soils in utility rights-of-way, railroad embankments, and the neglected edges of Tulsa's older neighborhood lots.

Within Oklahoma, P. digitalis occurs throughout the eastern half of the state, with the highest frequency in the Ozark plateau counties (Delaware, Adair, Cherokee) and the Cross Timbers (Osage, Tulsa, Creek), tapering westward into central Oklahoma. It is one of the most common and recognizable native penstemons in the region.

Ecology & Wildlife Value

[ bumblebee pollination · hummingbirds · lepidoptera · deer resistance ]

Pollination Syndromes

The large, tubular white flowers are primarily pollinated by bumblebees, which are among the few insects strong enough to push into the wide tube and trigger the lever mechanism of the stamens. In NE Oklahoma, the most frequent visitors are the common eastern bumble bee (Bombus impatiens) and the American bumble bee (B. pensylvanicus). Large carpenter bees (Xylocopa virginica) also visit, and occasionally ruby-throated hummingbirds probe the flowers for nectar. Smaller solitary bees and syrphid flies visit but are less effective pollinators because they cannot reach the nectar at the base of the relatively deep tube.

Lepidoptera & Other Insects

While Penstemon species are not major butterfly host plants, the foliage is consumed by larvae of the common buckeye (Junonia coenia) and is a secondary host for the baltimore checkerspot (Euphydryas phaeton) and a few moth species. More significantly, penstemon flowers support a diverse guild of pollen-collecting solitary bees, including Osmia (mason bees) and Anthophora (digger bees) that specialize on tubular flowers.

Deer & Rabbit Resistance

Penstemon digitalis is rated as strongly deer-resistant — white-tailed deer occasionally browse the flower stalks but generally leave the basal foliage alone, likely due to mildly toxic iridoid glycosides in the leaves. Rabbits may nibble young rosettes in early spring but rarely cause significant damage. This makes foxglove beardtongue an excellent choice for rural and suburban-edge gardens in the Tulsa area where deer pressure is high.

Seed Value

The tiny seeds are consumed by native sparrows (song sparrow, field sparrow) and other small granivorous birds foraging the dried stalks in fall and winter. While not a primary bird food like sunflower or coneflower seed, penstemon seed contributes to the diverse seed mix that supports wintering bird communities in a native landscape.

Horticulture & Care

[ easy establishment · cultivars · deadheading · companion planting ]

Site selection & establishment

Foxglove beardtongue is one of the easiest native perennials to grow. Full sun on any decent soil. It handles Tulsa's heavy red clay as well as sandy loam, and is more tolerant of poorly drained winter soil than almost any other penstemon. A few hours of afternoon shade are fine but will reduce flowering. Plant container-grown specimens in spring or fall; they establish quickly and typically bloom the first year if planted in spring.

Spacing: 12–18 in apart for mass planting; 24 in for specimen clusters.
Water: Water at planting and during the first month. Established plants are moderately drought-tolerant but look best with occasional deep watering during Tulsa's August dry spell.
Fertilizer: Not needed. Over-fertilized plants produce floppy stems.
Mulch: A light (1–2 in) mulch of shredded bark or leaves helps retain moisture and suppress weeds around the rosettes.

Deadheading & maintenance

Deadhead spent flower stalks promptly after bloom for a tidier appearance and to prevent self-sowing if desired (though self-sown seedlings are easily pulled or transplanted). If you want seedlings, leave a few stalks to ripen and shed seed naturally. Cut the dried stalks to the ground in late winter (February) before new growth begins. Divide congested clumps every 3–4 years in early spring or fall to rejuvenate.

Pests & diseases

Powdery mildew — occasionally on the basal leaves in humid, crowded conditions. Improve air circulation.
Root rot — rare but possible in poorly drained soil with standing water for weeks. P. digitalis is quite tolerant compared to other penstemons.
Slugs — minor damage to young leaves in wet springs.

Notable cultivars & selections

Cultivar	Description	Notes for Tulsa
'Husker Red'	2–3 ft; deep burgundy-purple foliage; white flowers with pink blush	1996 Perennial Plant of the Year; outstanding foliage plant even out of bloom; tolerates heat.
'Mystica'	2–3 ft; dark bronze-purple spring foliage maturing to green; pink-flushed white flowers	Similar to 'Husker Red' but with slightly darker spring color.
'Dark Towers'	3 ft; dark burgundy foliage all season; pale pink flowers	A P. digitalis × P. cobaea hybrid; broader, glossier leaves. Xera Plants introduction.
'Blackbeard'	3 ft; near-black emerging foliage, dark purple all season; lilac-pink flowers	Striking dark foliage; needs good drainage.

Companion plants

Foxglove beardtongue bloom coincides with the late-spring flush of the prairie garden. Excellent companions include golden alexanders (Zizia aurea) for yellow contrast, spiderwort (Tradescantia ohiensis) for blue-purple counterpoint, wild indigo (Baptisia australis) for structural backdrop, butterfly milkweed (Asclepias tuberosa) for orange pop, and eastern woodland sedge or Leavenworth's sedge as groundcover. For prolonged bloom succession, underplant with purple prairie clover or black-eyed Susan.