How to Grow Penstemons

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How to Grow Penstemons

Copyright © 2007 The Arboretum at FlagstaffLast modified: Wednesday May 02, 2007

Native only to North America, with 272 different species found from Canada to Mexico, and from the Atlantic to the Pacific, the genus Penstemon is truly remarkable. Penstemons are amazingly diverse in shape, form, and color, and they grow in many different environments, from low, dry deserts to high, moist forests.

Nearly all penstemons share a love for well-drained soils. Once established, they require very little water beyond what nature provides. Botanists and gardeners consider penstemons to be xeric, or water-thrifty plants. With their beautiful flowers (loved by pollinators like hummingbirds and hawkmoths), they are excellent plants for dryland gardens, especially here on the semi-arid Colorado Plateau.

Formerly the Groundcover Garden, the Arboretum’s new Penstemon Garden is a work-in-progress. This garden displays the diverse penstemon species of the high altitude West and Southwest. The garden’s south arm (farthest from the San Francisco Peaks) was planted in September 2003, and includes eight different Flagstaff-area penstemon species, from the rare Penstemon clutei (Sunset Crater penstemon), to Penstemon whippleanus (Gray Whipple's penstemon). Clutei is endemic to the volcanic soils around Sunset Crater, meaning that it is found nowhere else in the wild. Whippleanus grows in higher, cooler, and moister elevations than clutei. Take a closer look: the leaves of each species reveal these elevational differences, with the clutei displaying tougher, thicker leaves that conserve water. Other common native plants of the southern Colorado Plateau are growing as “companions” of the penstemons in this bed, like Quercus gambelii (Gambel’s oak).

The garden’s west arm (nearest the Horticulture Center) was planted in late June of this year. This bed features penstemons that are native to the larger Colorado Plateau bioregion and its edges. These include Penstemon eatonii, (firecracker penstemon) a red-flowered species that typically grows between 3,000 and 6,000 ft., and Penstemon neomexicanus, (New Mexico penstemon) a high elevation, blue-flowered species native to New Mexico’s Sacramento Mountains.

Like the south bed, the west arm is organized to show elevational differences: penstemons that typically grow in lower elevations (below 7,000 ft.) begin on the bed’s south end, while penstemons that prefer higher elevations (above 9,000 ft.) are planted on the bed’s north end, toward the San Francisco Peaks.

As mentioned above, nearly all penstemons grow best in very well drained soils. To improve drainage, gardeners added black volcanic cinders to The Arboretum’s clayish, poorly drained soils. The cinders also act as a water-saving mulch. In addition, we built small berms and added local “malpais” rocks (a kind of volcanic stone), to create slightly warmer microclimates.

Besides adding volcanic cinders to the soil, The Arboretum’s gardeners have also done a great deal of “hardscape” work, as part of the process of transforming the old Groundcover Garden into the new Penstemon Garden. Using malpais stones, we completely rebuilt the garden’s east-facing dry stack walls. No mortar was used to create these solid retaining walls.

Using mortar and flatter pieces of malpais we also re-capped the garden’s already existing concrete walls. We also designed and constructed two new interior beds with sandstone blocks and mortar, and removed the old dirt pathways, replacing them with “Sedona Red” crusher fines and “Stabilizer Solution.” This latter substance gives the pathways their hard texture.

In future years, the Penstemon Garden will continue to evolve and change. We will be planting many more native plants in this garden, focusing on the penstemon species of Utah and the Intermountain West.

We hope that you enjoy The Arboretum at Flagstaff’s beautiful and exciting new Penstemon Garden! We are grateful to the Margaret T. Morris Foundation for financial support in this ongoing project.

Penstemon Garden Species List

ambiguus
barbatus
brandegei
clutei
commarhensus
eatonii
linarioides
mensarum
neomexicanus
nudiflorus
palmeri
virgatus
whippleanus