Sometimes called beard-tongues, penstemons (Penstemon spp.) include 250 different species of plants that are deciduous or evergreen perennials. Native to sunny plains and meadows to alpine reaches in both North and Central America, their growing requirements varies based on the conditions of their native habitats. The reason gardeners love to grow penstemons is their display of clusters of tubular, two-lipped flowers on upright stems.
Importance of Penstemon Plant Identity
With such a large number of penstemon species, and many more hybrids, knowing the precise species name or parentage of hybrid plants helps gardeners provide the proper growing conditions. In general, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants," hybrid penstemon plants tend to be more short-lived than wild species types.
Knowing the species and native origins of the different penstemons also reveals how well they survive winter cold in North American gardens. Overall, there is a species or hybrid of penstemon that will grow successfully in USDA winter hardiness zones 3 through 10, but not all penstemons are appropriate for cultivation in all these zones. For example, among the most cold-hardy penstemons are the Wasatch beard-tongue (Penstemon cyananthus) and the crested beard-tongue (Penstemon eriantherus), both grown in zones 3 through 8. Conversely, penstemons best grown in warmer lands include the Parry's desert beard-tongue (zones 8 through 10) and the bellflower beard-tongue (Penstemon campanulatus), grown in zones 7 through 10.
Most penstemons grow best in sunny locations that receive at least six to eight hours of direct sunlight daily in the growing season. They can tolerate partially sunny to partially shaded spots, too, where sun rays last for four to six hours daily.
On the whole, penstemons grow best in soils that are not overly fertile. Hybrid types have been bred or selected to prosper in the moist, richly fertile soils common in most ornamental gardens and grow in any well-draining soil. Dwarf (alpine) and shrubby, evergreen-like penstemons are best grown in gritty, sharply (fast and thoroughly) draining soils that are devoid nutrients to only moderately fertile. A common dilemma in gardens is a penstemon that fails to flower well. This can be attributed to a soil that is either too moist or heavy in texture, or too rich in nutrients from fertilizers or organic matter.
As wildflowers, the majority of penstemons flower and produce many seeds that are strewn across the nearby soil. Overall, these plants are short-lived perennials, perhaps persisting as long as three to five years, but in general will diminish in vigor and be overtaken or replaced by newly sprouting generations of seedlings. Plan on propagating new penstemon plants from soft-stem cuttings in summer or sowing seeds in containers after being exposed to a winter season of dryness or cold temperatures. Or, simply purchase new plants from the nursery or allow seedlings to sprout up haphazardly in the garden.