Culture
Easily grown in average, dry to medium, well-drained soils in full sun. Plants have some tolerance for drought, summer heat and humidity. Avoid wet, poorly-drained soils. Remove spent flowering racemes to prolong bloom. Plants may be cut back to basal foliage after flowering to improve appearance of the planting. Plants in cold winter climates often benefit from a loose winter mulch.
Noteworthy Characteristics
Penstemon is a genus of about 250 species of herbaceous perennials and sub-shrubs which are primarily native to the continental U.S., Canada, Mexico and Guatemala in a variety of habitats ranging from desert to plains to alpine slopes. A large number of hybrids have been developed over the years, but most are of unclear parentage.
Genus name comes from the Greek words penta meaning five and stemon meaning stamen in reference to each flower having five stamens (four are fertile and one is sterile).
Penstemons are sometimes commonly called beardtongues because the unusual sterile stamen contained in each flower has a tuft of small hairs.
‘Red Rocks’ is a penstemon hybrid of unknown parentage that is sometimes listed as an x mexicali cultivar because the parents purportedly include species from both Mexico and the U.S. ‘Red Rocks’ was developed in Colorado, with the cultivar name referring to the Red Rocks Amphitheater carved out of red sandstone cliffs located west of Denver. It features showy spikes of two-lipped, tubular, rose-red and white flowers that bloom from early to late summer in loose upright terminal panicles atop stems rising above the foliage to 12-18” tall. Stems are clad with narrow medium green leaves.
Problems
Root rot can occur in wet, poorly-drained soils. Leaf spots, rusts, powdery mildew and Southern blight may also occur. Slugs and snails may chew on the foliage. Watch for spider mites. Deer tend to avoid this plant.
Uses
Sunny areas of borders, rock gardens, cottage gardens and open woodland areas.
Xeriscape.