Penstemons are a staple in Western gardens—and for good reason.
Certain types of these native plants thrive on heat and drought. They prefer poor soils and, once established, require little water.
They’re also gorgeous, growing up to 5 feet tall with strong stems and big, lovely, tubular flowers (similar to those of snapdragon and foxglove) up to 2 inches long. Blooms boast rich purples, soft pinks, showy magenta, snowy whites, clear and cobalt blues, and radiant reds. Flowers last up to four weeks and are magnets for butterflies, hummingbirds, and beneficial bees.
But penstemons can also be at home in cooler, wetter gardens. The key is choosing the right penstemon for your region.
Some Like It Hot
Sometimes called Western types or tall types, the showiest penstemons are those that perform best in hot, dry climates, putting on an incredible display in summer and fall. Many are hardy only in Zones 8 to 9. You can grow them as annuals in colder regions, but they won’t achieve the same size or show.
Rocky Mountain penstemon (Penstemon strictus, Zones 4 to 9) grows about 3 feet tall and 2 feet wide. Its deep lavender flowers are drop-dead gorgeous and last for months. This penstemon lives for many years, unlike others that survive just a few years in unfavorable conditions.
Pineleaf penstemon (Penstemon pinifolius, Zones 4 to 9) is outstanding but often overlooked. It has dazzling flowers that mimic the colors in a sunset. What makes it distinctive is the bright green needlelike foliage and woody habit. Pineleaf penstemon grows 15 inches tall and 18 inches wide.
Desert penstemon (Penstemon pseudospectabilis, Zones 5 to 10) grows up to 3 feet tall and 18 inches wide. It blooms most of the summer with spikes of hot pink flowers.
The Cool Kids
If you live in a colder, wetter climate, you can still enjoy penstemons’ brilliant blooms and easy-care attitude. Sometimes called Eastern types or prairie types, these plants demand good drainage.
One such penstemon, Penstemon digitalis ‘Husker Red’ (Zones 3 to 8) stole the limelight after it was named the 1996 Perennial Plant of the Year. Dale Lindgren, a leading breeder of prairie-type penstemons, hybridized ‘Husker Red’ at the University of Nebraska. It grows up to 30 inches tall, with white to pale pink blossoms and deep purple leaves and stems.
Penstemon ‘Sweet Joanne’ (Zones 4 to 8) is another excellent cold- tolerant penstemon. Named after Lindgren’s wife, it grows about 2 feet tall and wide with striking purple and white streaked flowers.
Purple Ozark penstemon (Penstemon cobaea, Zones 5 to 8) grows 30 inches tall with glossy foliage. Its lavender-purple flowers are so large that bumblebees fit comfortably inside them.
Penstemon ‘Red Riding Hood’ (Zones 5 to 8) grows 18 inches tall and wide with big, white-lipped flowers that are especially attractive to hummingbirds.
Rock gardens are a perfect setting for smaller penstemons. Unlike species that send flower stalks several feet up, diminutive rock-garden types grow just a few inches tall with masses of smaller flowers. They are often evergreen, and will tolerate moister soils than the Western types. Like all penstemons, they hate wet feet and need good drainage.
One of the larger rock-garden penstemons, Penstemon barbatus ‘Elfin Pink’ (Zones 3 to 8) grows about 1 foot tall and 6 inches wide. With pretty pink flowers, it’s one of the most cold- and moisture-tolerant of all the rock-garden penstemons.
Penstemon ‘Red Rocks’ (Zones 5 to 9) is a 1999 Plant Select winner. (The Plant Select program of Denver Botanic Gardens and Colorado State University recognizes plants with excellent hardiness and adaptability.) It grows 18 inches tall and 15 inches wide, and has glossy foliage and eye-catching rose-pink flowers.
How To Grow Penstemons
Full sun is a must. Plant penstemons in a spot where they’ll get at least eight hours of unfiltered, direct light—and 10 to 12 hours is even better.
Penstemons love dry soil, so drainage is key. If you don’t have well-drained soil, plant them in raised beds, berms, or slopes. Many penstemons are shorter-lived, lasting just a few years, and wet soil assures their early demise. Don’t use mulch around penstemons—they don’t like moist crowns. If you do mulch, use gravel instead of wood chips, pine needles, or other organic matter.
Deadhead regularly. Some penstemons will bloom for many weeks if you diligently trim their spent flowers.
Whatever you do, don’t pamper your penstemons. Fertilize and water sparingly. Penstemons prefer poor, dry soil and will flop if you fertilize them too much.
Penstemons are rather rangy, airy plants, so they look best in groups of a half dozen or more. Just one plant by itself can look a little messy and lost. Another bonus of planting them in masses: valuable pollinators like hummingbirds, butterflies, and bees are more attracted to groups of plants than single specimens.
With their long stems and intricate flowers, penstemons make a good cut flower. They’ll last three to five days in a vase. Their delicate flowers start to shatter after a few days, but until then, they are spectacular.
Veronica Lorson Fowler is a garden writer in Ames, Iowa. David Salman, president and chief horticulturist of High Country Gardens in Santa Fe, New Mexico, contributed to this article.
• Native Americans used penstemon roots to treat toothaches.
• Penstemon is commonly called beardtongue because of the often-hairy stamen that hangs out of the tubular flower.