Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Every year as the summer starts to heat up in June, penstemon starts blooming. The popular cultivar, Husker Red, is especially eye-catching with its stalks of white flowers towering over dark red foliage. It is truly a star in the early summer garden.
What is Penstemon?
Penstemons (Penstemon spp.) are herbaceous flowering perennials. There are 250 species that are native to North America. As a group, most of the species are hardy in zones 3 through 9. Some are only hardy through zone 5. Penstemons are drought tolerant plants, generally found in desert or other dry areas. They are often used in xeriscapes. Another added bonus is that deer stay away from them. They range in size from 1 to 3 feet. There is a penstemon for every part of the garden.
The flowers look a lot like foxgloves or snapdragons. In fact, they are related to them. They are all members of the plantain family. Penstemon derive their nickname, beardtongue, from the fact that a hairy stamen sticks out of the “mouth” of the flower. Some species have tubular flowers that are beloved by hummingbirds. The flowers range in color from red to pink to white and even purple. Bloom time is late spring through early summer.
How to Grow Penstemon
Penstemon should be grown in poor, well-drained soil. Once established, they are drought tolerant. An inch of rain a week is sufficient moisture for them. They do not need to be fertilized. Even compost is too rich for them. Mulch them with gravel rather than organic mulch. Gravel will keep the crowns of the plants dry. Organic mulches such as bark retain moisture and cause the crowns to rot.
Plant your penstemons in full sun. They are best planted in the spring, rather than the fall. When you plant them in the spring, the plants have the entire growing season to grow out their roots. These are drought tolerant plants, so they have a deep root system. If you plant them in the fall, they have only a short period to grow out their roots. They may not be able to grow roots deep enough to survive the winter when there is less moisture resulting in sickly or even dead plants in the spring.
Give the plants some room in the garden. They do not like being crowded. Most gardeners cut down the flower stalks when the plants have finished blooming, but if you leave the flower stalks, allow them to go to seed and then drop that seed into the soil, the resulting plants will be hardier than their parents.
How to Grow Penstemon From Cuttings
Penstemon can be grown from tip cuttings. Tip cuttings are cuttings that are taken from the ends of the stems and include the growing tip. The growing tip is the actively growing part of the stem. Take your cutting from late spring to fall from stems that are not blooming. They only need to be 2 to 3 inches long. Remove the leaves from the bottom inch or less. Dip the cut end in some rooting hormone and then gently press the cuttings into a container that is filled with pre-moistened soil. The cutting should be buried up to its first set of leaves. You will know that your cutting has rooted when you see new growth on it. Plants that don’t have roots can’t grow new leaves.
How to Grow Penstemon by Layering
Layering is an easy propagation technique that is even used by Mother Nature! You have probably seen plants where a stem has fallen over and rooted. You can do this with penstemon by very carefully bending a stem to the ground. To keep it in contact with the soil, use metal staples like the ones that are used to hold the fabric covering the tunnels that protect plants from cold in your garden in the spring. When you see new growth, just sever the stem from the main plant, carefully dig up the newly rooted root ball and transplant it to a new home elsewhere in your garden.
How to Grow Penstemon From Seed
Penstemon is what is known as a pioneer plant. That means that it is one of the first plants to move into an area that has been disturbed, burned, or eroded. Since plants themselves can’t move, it is their seeds that are distributed over these types of areas by animals and birds passing through. Penstemon is as easy to grow from seed in your garden as it is in the wild.
Two important facts to keep in mind about penstemon seed is that it needs a period of at least six months to dry. You should not try planting freshly harvested seeds. They will not germinate. This is a plant that needs a full growing season to develop its root system so it has evolved its seeds to dry out and wait until after winter has passed so that it will germinate in the spring.
The second thing to know is that germination is poor for the seeds. Again, this is an adaptation to its poor growing environment. In the wild, only a few seeds will germinate each year. The rest will be dried and waiting in the soil. This ensures that if a crop of seeds germinates into plants that don’t survive the growing season for some reason like too much rain, too hot, or too cold, that there will be a stock of seed in the ground that can germinate the following year and renew the plant population. So when planting the seed, always plant more than you will need. Not all of the seeds will germinate.
The seeds need a period of cold to germinate, so sow the seeds in your garden in the fall. The cold of the winter will aid the seed in germinating in the spring. The plants want their seeds to germinate in the spring so that they will have many months to grow their deep root system that helps them survive dry conditions.
Alternatively, if you are starting your seed indoors, you will need to fool them into thinking that winter has come and gone. Starting in March, surface sow your seeds in a container filled with pre-moistened soil and cover the container with a plastic bag. The plastic bag is to prevent the soil from drying out. Place the covered container in your refrigerator. This mimics the cold weather of winter. Check the soil weekly and mist to add moisture if the soil is dry. When seedlings start to appear, remove the container from the refrigerator and uncover it. Place the seedlings in a sunny window in a room that is 40⁰F to 60⁰F. You are trying to mimic cool early spring conditions. If you are using lights, set the timer on your lights to have them on for 14 to 16 hours a day. Once the seedlings have 2 to 3 sets of leaves, they can be transplanted into your garden.
Questions & Answers
Question: How far apart should penstemon be planted?
Answer: It depends on what kind of penstemon you are growing. They have a wide range of sizes. The taller ones need to be farther apart. A good rule of thumb is to plant things at least half as far apart as they are tall so 36-inch plants should be planted at least 18 inches or more apart. 12-inch plants should be planted at least 6 inches apart.
Question: How tall and wide does one beard tongue penstemon grow?
Answer: There are 250 different species of penstemon ranging in height from 1 to 3 feet.
© 2019 Caren White
Caren White (author) on June 29, 2019:
You're welcome, Bronwen! So glad to be able to entice gardeners to try new plants.
Bronwen Scott-Branagan from Victoria, Australia on June 20, 2019:
That's interesting that the penstemon is related to the foxglove and snapdragon. I love both of those, so your article has enticed me into trying to grow this one, too. Thank you.
Caren White (author) on June 20, 2019:
Thanks for pointing out the typo in the title! I have corrected it.
RTalloni on June 20, 2019:
Thank you for this introduction to pentstemon (penstemon?). Its flower is really pretty and that it does well in poor soil makes it ideal for dressing up out-of-the-way spots. Hopefully smaller animals will dislike it as well as deer.