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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 2005.
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 |
Copyright © 2007 The Arboretum at Flagstaff
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