Penstemon, commonly called Beardtongue, is a diverse and popular group of perennial plants native to North America. This genus contains nearly 300 species, appreciated for its striking, tubular blossoms and resilience. The flowers attract hummingbirds and various pollinators, making them a fixture in native and xeriscape gardens. Successfully integrating these plants requires understanding their geographic requirements to ensure winter survival.
How Hardiness Zones Apply to Penstemon
The primary tool for determining a perennial plant’s survival in a given area is the United States Department of Agriculture (USDA) Plant Hardiness Zone Map. This map divides North America into zones based on the average annual extreme minimum winter temperature. For instance, a plant rated hardy to Zone 4 can tolerate a minimum temperature range down to -30°F, while a plant rated to Zone 9 can only withstand temperatures down to 20°F.
This minimum temperature rating is the greatest predictor of whether a perennial will survive the coldest part of the year. Gardeners can determine their zone using their ZIP code on the USDA website to match their climate to the plant’s cold tolerance. Due to the diversity within the Penstemon genus, its overall hardiness range is expansive, generally falling between USDA Zones 3 and 9.
Most commonly cultivated penstemons are reliably hardy between Zone 4 and Zone 9, but this broad range reflects the plant’s adaptability across different biomes. Some alpine species are native to extremely cold environments, surviving in Zone 3, while certain Southwestern varieties thrive in mild-winter climates, stretching the genus to Zone 10. Selecting the correct species or cultivar is paramount, as a single zone rating cannot apply to the entire genus.
Matching Penstemon Species to Your Region
Because the Penstemon genus spans such a wide range of climates, specific species are best suited for different regional temperature profiles. For the coldest regions, the best choices are often those native to the Great Plains, which are adapted to extreme temperature swings and deep freezes. Penstemon grandiflorus, or Large Beardtongue, is an excellent example, with a documented hardiness range of Zone 3 to 9. Another notably cold-tolerant species is P. digitalis, commonly known as Foxglove Beardtongue, which is widely cited as hardy from Zone 3 to 8.
For gardeners in the intermediate climates of Zones 5 through 7, a wider selection of species and hybrids is available. The species P. barbatus, or Bearded Penstemon, is a popular choice for this middle range, typically thriving in Zones 4 through 9. Many garden center hybrids, such as those bred for intense color or extended bloom time, are specifically developed to perform reliably across these standard temperate zones. These varieties often represent a balance between cold tolerance and adaptability to a wider variety of garden soils.
In warmer regions, specifically Zones 8 through 10, the focus shifts to species that tolerate mild winters and intense summer heat. Penstemon eatonii, known as Firecracker Penstemon, is a native of the southwestern United States and is hardy from Zone 5 to 10, making it heat and drought-tolerant. Similarly, P. heterophyllus, or Foothill Penstemon, is well-suited for Zone 7 to 10 conditions, relying on its adaptation to dry, rocky slopes. Matching a plant’s native environment to the local climate, rather than just its minimum temperature, ensures long-term success.
Other Essential Elements for Penstemon Survival
While the hardiness zone defines a plant’s ability to withstand cold, other environmental factors determine its survival and health. The most significant non-temperature factor for most penstemons is soil drainage, as the plants are susceptible to root rot. They typically require poor, well-drained, or gritty soil. Gardeners often find that heavy clay or overly rich garden soil can lead to plant failure, particularly during periods of winter wetness.
Most species are native to dry, open habitats and require full sun exposure. Sunlight encourages strong growth and contributes to overall plant vigor. Established penstemons are generally drought-tolerant, reflecting their prairie and desert origins. Overwatering or prolonged exposure to saturated soil remains the most common cause of decline, regardless of the zone a plant is grown in.