Santa Fe Botanical Garden

Common name: mat penstemon

Family: Plantaginaceae (Plantain)

Distribution: Colorado, Wyoming, Utah, Arizona

Habitat: Prairies, sagebrush scrub

Hardiness: USDA Zone 4 (-30 to -20 °F)

Life form: Shrub/sub-shrub

Occurrence in New Mexico: Exotic

Growing Conditions: There are 3 varieties of P. caespitosus: var. caespitosus grows among sagebrush in northern Colorado, southwestern Wyoming, and northeastern Utah; var. perbrevis is found in east-central Utah; and var. desertipicti is native to canyons of southern Utah and northern Arizona. Penstemons need dry, gritty, gravelly or sandy well-drained soils. They are easy to grow in New Mexico and failure is almost always due to excessive moisture after flowering. They grow in soil of low organic content and are short-lived in soil that is too rich. Soil must drain quickly so that the plants’ crowns remain dry. Supplemental water in the first year helps them to become established, but they generally do not need to be watered thereafter. Even during droughts, they should not be watered more than once weekly. In general, penstemons prefer dry soil in winter and some protection from intense winter sun. Like other xerophytic plants, they often die off after 1-3 years after blooming abundantly. Cutting back plants after flowering may increase longevity. A few stems can be left to promote self-seeding. This mat-forming penstemon will live for many years if not subjected to too much water. It sometimes roots at the nodes and var. caespitosus may spread rapidly.

Description: This prostrate penstemon often roots at the stem nodes, sometimes forming mats up to 3 feet wide. The small leaves (less than ⅜ inch long) are gray-green and hairy, and may be linear, oblong, or narrowly lance-shaped. The tubular flowers are about ½ inch long with a gradually widening, bulging throat with two ridges on the upper side. The tube and throat are lavender outside and white within, and the lobes are blue. Inside the flower throat are red-violet lines. The staminode (sterile stamen) has a golden beard. The anthers are open full length, with toothed edges along the openings.