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Penstemon — beard tongue

 

The genus

Penstemon — a genus of well over two hundred species, including annuals, biennials, perennials, and subshrubs, all native to North and Central America. They are classified in the plantain family (plantaginaceae), at least that's what the latest version of GRIN says. They used to be classified in scrophulariaceae, but along with the snapdragons (antirrhinum) and foxgloves (digitalis), they've been shipped out. Not that it matters too much which botanical company they hold - the genus is big enough to hold its own.

The genus name derives from the Greek words πεντα (penta: five) and στημων (stemon: thread), referring to the five stamens within their flowers (one of which is sterile). The common name describes the fuzzy feature on the bottom lips of the flowers, not unlike the beards in bearded irises.

Cultivation

As wildflowers, penstemons are widely distributed across North America, making their home in habitats ranging from plains to mountain areas. While some species require more moisture than others, all appreciate well-drained soil, and many insist on it. Full sun is best for most, although some do fine in part shade. Luckily for me, the majority are hardy in our garden in USDA zone 6 (and many can tolerate quite a bit colder climates).

A few species have been long-lived for us (P. hirsutus var. pygmaeus and P. pinifolius, for example), but more commonly the plants fade away after a few years, and must be replenished periodically. We've had quite a number of generations of P. strictus by now - but they're nice enough to warrant the effort.

Propagation

All of my beard tongue multiplication efforts proceed via seed. I imagine most species can be divided without too much trouble, but for some reason I've never tried. Penstemons aren't always easy to start from seed - germination requirements vary widely from species to species, many requiring cold conditioning and/or light, and often not responding even when "by-the-book" conditions are provided. An extensive overview of penstemon germination requirements (or suggestions) is given at a few pages in Tom Clothier's Garden Walk and Talk website.

My own experience is that some species are really quite easy to establish by seed, while others always seem to give trouble during germination, and/or resent the conditions I provide during growing-on in the basement. Still, I germinated enough of 'm that I have some purdy pictures to show on this page. I provide detailed records of my germination attempts on many of the individual species portraits linked from this page. That's only for the ones I've successfully grown, though - for species I never managed to germinate and grow on, I won't bother you with the negative results.

Penstemon seeds are angular particles, usually easily extracted from spent flowers. Their color ranges from tan to black. Seed stays viable for a year or two, but loses viability in subsequent years. Interestingly, a penstemon-fanatic seed trading partner told me that very fresh seed often does not germinate well, or has additional germination requirements (cold or light) when fresh, which are no longer required with stored seed. So perhaps year-old seed is best.

Beard tongues in the garden

None of the penstemons we grow rise above three feet, and many of them are a good bit shorter than that. Somehow, I don't see them as lending themselves to mass plantings (although I may be wrong!), so in our garden they serve as accents - punctuation marks between plants of larger scales or bigger bulk.

Many have an upright, somewhat sparse or lanky habit, working effectively when weaving in with other plants with similar habits but different overall appearance. The bushier ones tend also to be shorter, making good front-of-the-border plants. This of course goes for the truly diminutive P. hirsutus var. pygmaeus, but also holds for P. smallii.

The best place for many penstemons is probably not in a traditional border, but in the rock garden. That's where our P. pinifolius lives, but would also be a better station for others we've grown and lost - especially P. heterophyllus, which always seemed a bit lost in a regular garden setting.

The leaves

Penstemon foliage varies quite a bit in shape, color, and habit. Leaves are oppositely arranged, and as far as I know always undivided. Extremes vary from needle-shaped leaves to rounded and lax, from glossy to mat, from toothed to entire. A few examples are shown below.
P. cobaea: glossy, mid-green, slightly serrated leaves, sparsely arranged along stalk P. hirsutus var. pygmaeus: dense mat of dark-green, strappy leaves P. x mexicali: bright green serrated strap-shaped leaves, neatly arranged along stems
P. pinifolius: as the species name suggests, this one has needle-like leaves, arranged in bunches like pines. This P. digitalis is purportedly 'Husker Red' - probably a seed strain, since its burgundy color doesn't hold up well as it should. P. heterophyllus has smooth-edged, strappy gray-green leaves.
Classic opposite arrangement of serrated leaves on P. smallii. Substantial blue-green leaves clasping the stem on P. wrightii.

Flowers

Leaves are all good and well, but I don't know anyone who actually grows penstemons for their foliage. This bunch packs its primary punch in bloom! Although the basic features of the flowers in the genus are the same, there's plenty of variety:
P. cobaea has the largest flowers of our penstemons; it's almost gaudy! P. heterophyllus sports clear blue tube flowers. P. hirsutus makes cheery flowers with soft lavender exteriors and white interior. As the species name suggests, they are soft-hairy. Its diminutive cousin P. hirsutus var. pygmaeus looks quite a bit different; the first one we grew was shiny purple on the outside with more of a flattened shape. P. whippleanus goes for a sleek plum purple look, with stripes inside
P. smallii's white-hairy flowers are borne in great numbers P. pinifolius's masses of lipstick-red thin tubes put the neighbor's sportscar to shame. P. triflorus returns to the bold pink-spectrum flowers, albeit a bit more refined than cobaea. P. digitalis shows off charming rounded flowers by the bunch P. cardinalis ssp. cardinalis features striking carmine-red tubular flowers with a hint of a yellow beard.
This P. x mexicali 'Red Rocks' has showy, but smaller flowers. P. strictus is another blue one (I particularly like the blues). Smooth texture and conspicuous stamens. P. wrightii has slightly downy flowers, uniformly colored in a very pleasing shade of deep pink.

In winter

Most penstemons in our garden are squarely in the deciduous corner - not much to look at during the cold months. But a few species continue to provide interest through winter. The two photos below show examples:

The leaves of P. hirsutus var. pygmaeus, at left, go limp but turn a bright purple color (this photo was taken in February). As for P. pinifolius, it maintains its needles almost as well as real pines - although it tends to look a bit messy with the autumn leaves it collects.

Other species

A seed trader this year tempted me to start a whole bunch of new penstemon species. Although I'm sure not all of them will germinate, and of those that do not all will survive their first year, I still hope to have plenty more varieties to add to this page soon. Stay tuned!

Further reading

A useful link collection is provided in the Open Directory Project's penstemon category . You'll find an extensive list of species with identification information on the website of the American Penstemon Society.


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Last modified: May 27, 2015
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