Penstemon is one of our more spectacular native plants. Found in mountainous areas and their foothills, the herbaceous species is a temperate zone darling and thrives in most areas of the western United States. Also called Penstemon beard tongue, the plant produces dozens of tubular flowers arranged on a tall stalk. Learn how to grow beard tongue plants and you will have the birds, bees and butterflies doing summersaults to get at the plentiful blooms and their sweet nectar.
I. Appearance and Characteristics
Penstemon , the beardtongues, is a large genus of roughly 280 species of flowering plants native mostly to the Nearctic, but with a few species also found in the North American portion of the Neotropics. It is the largest genus of flowering plants endemic to North America. As well as being the scientific name, penstemon is also widely used as a common name for all Penstemon species alongside beard tongues.
Formerly placed in the family Scrophulariaceae by the Cronquist system, new genetic research has placed it in the vastly expanded family Plantaginaceae. The total number of species is uncertain due to ongoing research into if some of the named species are actually subspecies or misidentifications of already identified species.
They have opposite leaves, partly tube-shaped, and two-lipped flowers and seed capsules. The most distinctive feature of the genus is the prominent staminode, an infertile stamen. The staminode takes a variety of forms in the different species; while it is typically a long straight filament extending to the mouth of the corolla, some are longer and extremely hairy, giving the general appearance of an open mouth with a fuzzy tongue protruding and inspiring the common name of “beardtongue”.
Most penstemons form a durable woody stem (a caudex) and have persistent basal leaves, but some are fully deciduous perennials, the remainder being shrubs or subshrubs. Heights can range from 10 cm to as much as 3 meters. Along with their variable growth forms the penstemons have highly variable leaves, often with different leaf shapes on different parts of the same plant. Some species have highly reduced needle like leaves and others broad and rounded leaves, with their texture also running the range of hairy to smooth/glaborous. In the view of penstemon expert Robert Nold the defining evolutionary characteristic of the genus is adaptation to drought, as demonstrated by their numbers and diversity in the interior west of North America.
The one Asiatic species previously treated in Penstemon is now placed in a separate genus Pennellianthus. This leaves Penstemon a mostly Nearctic genus, with a few neotropical species. Although widespread across North America, and found in habitats ranging from open desert to moist forests, and up to the alpine zone, they are not typically common within their range.
II. How to Grow and Care
Keep the penstemon flowerbed weeded regularly. A 3-inch layer of organic mulch can help to control weeds, and rock mulch is also a suitable choice. You can cut the spent flower stems back after blooming to help plants look tidy. Penstemons don’t compete well with other plants, so give them plenty of space in the garden.
Sunlight
Penstemon plants need full sunlight to perform their best. Not only does this ensure that they put out quality blooms, but it also prevents them from flopping and reduces the risk of the plant developing powdery mildew on the leaves, especially in humid summers.
Temperature and Humidity
Most penstemons are cold-hardy to about 24°F. In summer, they tolerate temperatures into the 90s. They grow in a range of humidity levels, depending on the variety.
Watering
Penstemons tolerate drought, but 1 inch of water per week in the summer will keep plants vigorous and promote better blooming.
Soil
The soil for beardtongue must drain very well. These plants are prairie natives and prefer rocky or sandy lean soil types rather than rich garden loam. It’s fine to amend the soil with compost to achieve proper tilth but avoid manure applications.
Fertilizing
Don’t give penstemons compost or aged manure; it is too rich for the plants. Instead, apply an organic fertilizer only once a year, according to the manufacturer’s instructions.
Planting Instructions
In general, penstemon plants grow best in infertile, well-draining sandy or gravelly soil. They don’t tolerate clay soil or rich soil.
Sow penstemon seeds outdoors in fall or winter. Choose a location with well-draining, not rich, soil that receives full sun during the growing season and cover them with no more than a 1/4 inch of soil. The seeds require a period of cold weather, called stratification, before germination. Plants grown from seed may not bloom the first season.
A quicker method to acquire flowering penstemon is to buy nursery plants. In spring, plant them shallowly in the garden, spacing them 12 inches apart and making sure the top of the root crown is slightly above the soil line.
Pruning
To winterize the plant, cut all the foliage to about 2 inches above the soil line in late fall or early winter. During the growing season, remove individual stalks that have flowered at the soil line unless you want the plant to self-seed with the copious amount of seed it produces.
Propagation
Penstemon can be propagated by division, stem cuttings, and seed.
- To propagate by division
Dig up a mature penstemon in early spring. Cut apart the root system, making sure that each division has a portion of the roots. Plant the divisions back in the garden and water them or plant them in containers to give away.
- To increase your plants with stem cuttings
To take cuttings, cut a 5-inch section from the tip of a healthy penstemon plant just below a leaf node. Remove the leaves from the lower half of the cutting. Dip the bottom of the cutting in rooting hormone and insert it into a planting medium containing sand and perlite. Cover the pot with a plastic bag that has holes poked in it to combat condensation, and keep the cutting in filtered light in a warm environment.
Lift the bag daily, misting if the planting medium is dry. After three or four weeks, gently lift the cutting to see if roots have developed (they should be at least 1/2 inch). If so, repot in a slightly moist potting mixture. If not, return them to the pot and check again in a couple of weeks.
- To grow from seed
If your penstemon isn’t a hybrid, you can harvest seed from a mature plant approximately six weeks after it blooms. Cut a flower stalk several inches beneath a seed head and place it in a bag to dry for at least a week. After it is dry, pinch the seed head to release the seeds. Plant them outdoors in the fall, as you would with purchased seeds, for plants the following season.
Overwintering
Don’t bother to cut away any foliage during the winter, as this can help protect the plant. A thick layer of fallen leaves can provide plenty of additional protection.
Pests and Diseases
Penstemon plants attract spider mites, pests that can be controlled with a strong spray of water or insecticidal soap or neem oil.
A too-damp environment can lead to botrytis leaf mold or powdery mildew. Provide good air circulation around the plants and don’t water the plants from the top.
A microscopic nematode called an eelworm can inhabit the soil around the roots of the plant. Litte can be done for the plant at this point; it is best to remove and destroy it. Before planting new plants, replace the soil in the area where the infested plant grew to prevent reinfection.
How to Get to Bloom
When placed in the garden, give the plants plenty of room, about 1 to 3 feet apart. Add in a little compost if your soil is lacking in nutrients. Water the plants at least once a week when they’re young and use generous mulch to cut down on weeds that compete for nutrients and light. Mulch will also help protect the roots from cold snaps.
III. Types of Penstemon
- ‘Dark Towers’ is similar to Husker Red, but with pale pink flowers and darker foliage.
- ‘Elfin Pink’ is a good rock garden plant, topping out just shy of 12 inches.
- ‘Husker Red’ is perhaps the most well-known variety, due to being named perennial plant of the year in 1996; it features reddish-purple foliage and white flowers.
- ‘Jingle Bells’ has reddish-orange flowers that are beacons to hummingbirds.
- ‘Piña Colada’, a series of cultivars, features blue, rose, or white flowers on compact plants.
- ‘Red Riding Hood’ has red flowers and an upright growth habit.
IV. Uses and Benefits
In early summer, right after your spring bloomers have faded, they fill the garden with spires of foxglove-like flowers in hues ranging from soft pinks and lavenders to bold, fiery reds and electrifying blues. In addition to offering a broad palette of colors, these native wildflowers and their many cultivars come in many shapes and sizes, from dwarf varieties you can tuck into rock gardens to waist-high prairie plants that bring color and movement to the back of the border.
Penstemon beard tongue also makes an excellent cut flower, which will last for at least a week.
