Adventures in penstemon breeding

Although primarily woody plant breeders, Premier Introductions Inc. dabbles with a few select perennials including Baptisia, Iris, Muhlenbergia, Platycodon, Penstemon and Spigelia. Penstemon is an overlooked and under-appreciated genus with 280 species spread across the U.S. Most are concentrated in the west with several in the East/Midwest/Southeast. The American Penstemon Society (penstemons.org), now over 70 years old, offers a bulletin, seed exchange and discussion groups.

Penstemon digitalis ‘Husker Red’, with purple-green leaves, bell-shaped, white flowers, proved the game changer, and the plant became a garden staple. Bred by Dale Lindgren, University of Nebraska, was introduced in 1983 and received the Perennial Plant of the Year award in 1996. ‘Husker Red’ grows 28-32 inches high and 15-18 inches wide. In the Dirr garden, neither deer nor rabbits have eaten it or the many stray seedlings. Bees and hummingbirds are frequent visitors during the May-June flowering period. If dead-headed, reblooming may occur. The flower stalks and dehiscent capsule fruits are polished maroon and quite attractive. Requires only full sun and well-drained soil. Extremely heat tolerant based on performance in the Dirr garden, although the purple foliage color is diminished or lost in summer. Listed as Zone 3 to 8.

Many deep purple leaf cultivars have been introduced post ‘Husker Red’ including ‘Blackbeard’, ‘Dakota Burgundy’, ‘Dark Towers’ (2007 by Dale Lindgren), ‘Pocahontas’, and ‘Midnight Masquerade’. ‘Husker Red Improved’ is described as having deeper red-purple foliage than the original but I have yet to witness the cultivar in commerce. Tony Avent, founder of Plant Delights Nursery, considers ‘Blackbeard’ the best of the purple leaf types. It’s listed as a hybrid between P. digitalis and P. calycosus.

The Dirr ‘Husker Red’ seeded around with many variations of red-purple foliage. In 2020, seed was collected from the deepest red-purple foliage form and surface sown (12-21-20) on peat-based germination mix under intermittent mist (six seconds/hour), 70°F bottom heat, with prolific germination (1-4-21).

The three best were propagated and are available through Griffith Propagation Nursery (www.griffithnursery.com). All produce lavender white, bell-shaped flowers atop 18- to 24-inch upright stems in May (Athens). A few flowered the first year; all the second year. Foliage overwintered in pristine condition in above-ground containers when exposed to 2° F in December 2022. One has narrower leaves and deeper red-purple winter leaf color.

Excess seedlings were shared with fellow gardeners or discarded as PII did not want to fill the growing space with Penstemon. I planted six seedlings in daughter Katie’s garden with a resultant surprise, compact, 15-18 inch high flowering mound.

The majority of Penstemon species do not tolerate heat, humidity and inadequate drainage. Most references touted P. digitalis as reliable and persistent. As mentioned, ‘Husker Red’ is a P. digitalis selection. In Herbaceous Perennial Plants, Armitage referenced an Ohio colleague who reported this was the only Penstemon with which she was successful.

The American Penstemon Society (Bulletin 81, 2022) featured a report by University of Idaho researchers who trialed 194 of the 280 species and rated them best of the garden, good or unmitigated failures. The bulk of the species were western with no northeastern/southeastern in the best category. P. digitalis was not included.

Premier Introductions Inc. posited the question concerning utilizing eastern/southeastern species to introgress heat tolerance, garden longevity, unique flower and foliage colors, compact habits and reblooming traits into hybrids. The only native species I observed in a garden setting was P. smallii with pink to purple, tubular flowers. It is described as short-lived but a prolific seeder.

P. calycosus, long tube beardtongue, is native to most states east of the Mississippi. The flowers varying from pale lavender, pink to rich violet.

P. hirsutus, northeastern beardtongue, with purple-blue and white flowers, is native to the Midwest and Northeast. Variety albus, minimus, pygmaeus and ‘Blue Foam’ are listed.

P. gracilis, slender beardtongue, produces pale lilac/violet flowers. Occurs in upper Midwest, Plains States and into Canada.

Six species native to Georgia include P. australis, southern beardtongue; P. canescens, Appalachian beardtongue; P. calycosus, long tube beardtongue; P. dissectus, cutleaf beardtongue; P. laevigatus, eastern beardtongue; and P. pallidus, pale beardtongue.

Seeds/plants of most of the above have been sourced and are in the process of being tested for adaptability to nursery production before crosses are made. Many of the above evolved in prairie habitats, dry sandy woodlands, forests edges, moist meadows, bottomlands, limestone ledges and shale barrens. For most, good drainage is essential. They have yet to experience excess water on the foliage from overhead irrigation, media that is often too wet or dry, root temperature of 120°F in black containers. The early serendipitous breeding with P. digitalis confirmed the species adaptability to these conditions and I believe the window is wide open for improvement using eastern/midwestern/southeastern species.

To date (July 2023), the following taxa were germinated with seedlings transplanted to one-gallon containers.

• P. barrettii (from Penstemon Society and western in distribution)
• P. caespitosus
• P. digitalis- purple leaf seedling selections
• P. digitalis ‘Gold Foil’
• P. digitalis ‘Husker Red’
• P. gracilis
• P. hirsutus
• P. hirsutus var. albus
• P. hirsutus ‘Blue Foam’
• P. hirsutus var. minimus
• P. hirsutus var. pygmaeus
• P. pallidus
• P. smallii

Sourcing Penstemon seeds was an adventure. Prairie Moon Nursery in Winona, Minnesota (www.prairiemoon.com) offers native species. I found a terrific assortment of species, varieties, and cultivars from Plant World Seeds, St. Mary’s Church Road, UK, TQ12 4SE (info@plant-world-seeds.com). The three gems were P. smallii, P. digitalis ‘Gold Foil’, and P. hirsutus var. pygmaeus.

Never know how true-to-type seeds will prove. The P. digitalis ‘Gold Foil’ seeds resulted in purple, green and yellow/gold leaf seedlings. The yellow/gold offers a color break from green/purple and might prove a game changer like ‘Husker Red’. The penstemon journey has just begun for PII.