Flowering stems of firecracker penstemon (Penstemon eatonii) pop with color, adding a burst of red flowers to landscapes during the summer (Figure 1). These plants are just one of about 270 species of penstemon worldwide. Collectively, penstemons are commonly known as beard-tongue because of the stamens that protrude from the flower, resembling a hairy tongue.
The brilliant red tubular flowers, which are born on long stalks, attract hummingbirds. Although this showy perennial is native to arid regions of the western United States at elevations from 3,000 to 11,000 feet, firecracker penstemon plants are adaptable to other sites. In Missouri, these plants are best grown in full sun in well-drained soils, especially those with low fertility. When flowering, plants reach about three feet-tall.
Firecracker penstemon plants may be a bit difficult to find but seeds can be purchased online. For seed germination, a cold-moist period of stratification is required. Stratification can be accomplished by planting seeds in soil outdoors at a shallow depth in the fall or by sowing them indoors on top of potting mix in a container and covering them with 1/8 inch of the mix. After watering the potting mix lightly, place the containers in a refrigerator for about 112 days. After this time, remove the container from cold storage and place it in a warm area for seed germination.
Small seedlings can be transplanted to induvial pots. After the danger of frost has passed (around May 10 in Missouri), planted containers can be safely placed outdoors or plants can be placed in a flower bed, rock garden, or xeriscape. Take care to maintain low fertility, water plants infrequently, and remove spent flower stalks for reblooming. When plants become crowded, they can be divided in spring or fall.
Unlike their red-flowering, firecracker relative, five of the seven penstemon species found in wild Missouri habitats produce mostly white flowers (Figure 2). P. cobaea ssp. purpurea and P. grandiflorus bear purple or lavender flowers, while P. tenuis produces pinkish-purple blooms (Figure 3). Three species, including P. digitalis, P. pallidus, and P. tubaeflorus are distributed in many counties, except for those in the northwestern part of the state. P. arkansanus and P. cobaea are primarily found in counties that border Arkansas.
In contrast, P. grandiflorus is only found in Atchison County, whereas P. tenuis is only found in Dunklin County in the opposite part of the state. Sunny glades, tops of bluffs, abandoned fields, quarries, and roadsides are common sites for wild penstemon in Missouri. Plants and seeds of several penstemon species are available from wildflower nurseries.
Penstemons are short-lived perennials that grow in clumps and naturally reseed themselves to repopulate the landscape. Plants occasionally fall over from root lodging when the taller-growing species, such as P. digitalis and P. grandifloras are exposed to windy conditions with heavy rainfall. Penstemon plants are generally pest-free but can develop root rot diseases if overwatered or planted in poorly drained soils.