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Penstemon [PEN-stem-on] is a genus of herbaceous perennials containing about 250 species.
Most of these plants are native to the Nearctic region and parts of North America.
The variety of species makes it the largest genus of flowers in North America.
Penstemon is commonly called the beardtongue genus and the plants often called beardtongues.
Penstemon comes from the Greek words for five and stamen as each flower contains five stamens.
Four stamens are fertile, and one is sterile.
The sterile stamen features a small tuft of hair, leading to the common name beardtongue.
Size and Growth
Most penstemons are semi-evergreen perennials, while others are shrubs.
The height can vary between several inches to several feet.
Flowering and Fragrance
The most common characteristic of plants in this genus is the infertile stamen on the flowers.
The staminode is often long and extends through the corolla, resembling an open mouth or lips with a beard.
The unique appearance of the flowers inspires the common name “beardtongue.”
Blooms typically appear in late spring or early summer, depending on the cultivar. Penstemons are considered one of the best summer flowers.
The flowers tend to fade quickly, but the bloom time is extended by pruning dead stalks.
Light and Temperature
Grow penstemons in full sun or partial shade.
They can grow under the shade of taller plants in the garden.
Most species of penstemon flowers are considered winter hardy in regions experiencing frost.
It’s recommended for USDA hardiness zones 6 to 8, which includes most of central North America.
NOTE: Long periods of cold and wet conditions may kill the flowers.
If grown as a potted plant, avoid placing in a spot receiving direct afternoon sunlight.
The bright UV rays may damage the flowers.
Watering and Feeding
Penstemons often need medium moisture.
Water once or twice per week during the spring and summer, cutting back as the weather becomes cooler.
Use a general-purpose plant fertilizer in the spring.
The plant shouldn’t need fertilizer throughout the rest of the year.
Plant food encourages optimal growth before the flowers arrive.
Soil and Transplanting
Most species of penstemon plants need standard potting soil with good drainage.
Depending on the climate and species, rich soil may result in healthier growth and fuller blooms.
Transplanting is typically only needed when a container plant outgrows its container.
Refreshing the soil of container plants every few years is also recommended to provide the plant with more nutrients.
Cut back wilted foliage in the fall or before the first frost of winter.
This helps protect the plant during the colder months.
In the spring, cut back the foliage by at least two-thirds.
Grooming after the last frost allows for fresh growth at the start of spring.
How to Propagate Beardtongue
Depending on the species, propagate penstemon using cuttings or seeds.
If the plant flowers and produces seeds, collect the seeds at the end of the bloom season.
- Store the seeds overwinter in an envelope.
- Sow seeds in 5″ or 6″ inch pots.
- Scatter the seeds over moist soil and cover with a light layer.
- Place the pots in a bright, warm spot and wait for the seedlings to appear.
- After the stems appear erect and sturdy, transplant the penstemons outdoors or separate to individual pots.
To propagate with cuttings, select a soft branch without a flower.
- Cut the branch below the joint of a leaf.
- Remove the lower set of leaves from the cutting.
- Place several cuttings in a small pot filled with compost.
- Use a cold frame or shelter the young plants from the wind.
- Within four to six weeks, the plants should take root and become sturdy enough for transplanting.
Learn more about other Easy Perennials to Grow from Seed.
Beardtongue Pest or Disease Problems
The most common problems include thrips, aphids, and mildew.
Treat infested plants with insecticidal soap.
Mildew often develops due to excess moisture.
Improve the drainage of the soil by adding gravel or sand and limit watering.
Excessive mildew may kill the plant.
If the powdery growth spreads too far, try propagating the plant by selecting a healthy section for cutting.
Another potential issue is the spread of the plant.
Penstemon species tend to spread slowly through seed distribution.
The roots may eventually spread to nearby plants or overtake yards.
NOTE: It may take several years for a mature plant to spread, providing plenty of time to control the growth.
Penstemon plants are not considered toxic, but ingesting the plant may give animals excess selenium.
Extremely high levels of selenium may lead to various health problems in small animals and livestock.
Suggested Penstemon Uses
The trumpet-shaped flowers can add a blanket of color to a yard every spring.
More on other Favorite Perennial Plants and Flowers for the Garden
In hot or cold climates, it grows in containers and placed near windows or porches.
Consider using a mixture of species to add a combination of colors, including white, pink, red, lavender, and purple.