By: Y. Henson, L. Langelo, 2/2021
- Penstemons grow in rock gardens, slopes, raised beds, troughs, pots, containers, traditional perennial border.
- Penstemons attract hummingbirds, butterflies and bees.
Why Grow Penstemon?
There are many Penstemons that are native to Colorado (Nebraska). There are about 280 species of penstemon native to North America, 60+ native to CO and 24 natives to the Great Plains, including Nebraska which has about native 10 native species. However, there are other nonnative species and selections that grow in Colorado and Nebraska. There are many benefits for using penstemon in home and commercial landscapes including naturally adapted to their specific Colorado/Nebraska climate, soil, and environmental conditions. When correctly sited, they do well on reduced inputs such as watering, fertilizing, and pruning. Penstemons can be used in a variety of environments from low desert to alpine. Using Penstemon in the landscape can bring you a variety of color from May through July. A few blooms later at high elevations and others have a second bloom later in the season. These plants range from herbaceous to woody. Though most live for many years, some are short-lived while others are biennial. This variety widens their use in the landscape making them more versatile.
Other benefits of using Penstemon native to Colorado/Nebraska is the increase in attracting pollinators. With the rapid urbanization of Colorado/Nebraska adding these plants to our landscapes helps to maintain biodiversity that might be lost to development such as building developments and road construction.
There are many options for the use of penstemon in the landscape. Alpine, mixed shrub borders and rock gardens are also other uses. Many of the smaller varieties do well in troughs. When penstemon are utilized as bedding plants, they require warm well-drained soils with regular watering. They will bloom for a long period and perform best in soil with a long, mild summer and fall. Some examples of these are half-hardy hybrids like ‘Twizzle’ series, ‘Delfts Blue Riding Hood’, ‘Red Riding Hood’ and ‘Prairie Twilight’ mixes or seed strains. If penstemon is used in a traditional perennial border, interplant other perennials with similar cultural requirements to extend the season’s color. Large-flowered European hybrids, eastern species, and their cultivars along with west coast penstemons are the best for zone 6 and above. Canadian and US hybrids, northern, mid-western and eastern species and their cultivars are used best in zones 5 and below. Many of the tender new hybrids and species like Penstemon heterophyllus are all good choices for containers. Repeat flowering is important for container-grown penstemon.
Here are a few of the newer cultivated penstemon selections to try growing in the landscape, listed as follows: Blanca Peak Rocky Mountain Beardtongue, Penstemon strictus; Compact Pineleaf Beardtongue, Penstemon pinifolius ‘Compactum’; Electric Blue Foothills, Penstemon heterophyllus ‘Electric Blue’.
Penstemons are a low maintenance plant. However, some of the plants listed in the table can only be started from seed. Whether from seed or from a young plant, this does not mean they can grow successfully anywhere at any exposure. Chose a native or wild species that closely matches the type of soil, temperature range and precipitation of your landscape environment. You must understand what soil and exposure you have on your sites. Be sure to make use of the many micro-climates in your landscape to help find a place for a special penstemon.
Most penstemons require six hours of full sun to produce erect stems that produce flowers of clear and bright colors able to withstand wind and rain damage. As your elevation increases, the need for six hours of full sun decreases. However, there are some that prefer afternoon filtered light or shade. The higher the altitude or the hotter the climate, penstemon will bloom longer with some afternoon shade.
Penstemon requires good aeration and drainage. Good drainage and aeration are required for the crown of penstemon plants. Avoid planting in locations with standing water. Before planting, amend the soil with humus, fine gravel, and compost to add pore space to improve soil drainage and appropriate moisture retention and mix these ingredients in to a depth of 12 inches. The best amendment is a finished compost made from leaf mold. A finished compost changes soil structure well in all types of soil mixtures. Sites with a sand and gravel mix allow the homeowner to accommodate a wider selection of penstemon, especially allows for drainage. Most penstemon prefer a slightly alkaline pH above 7.0. However, this requirement varies with the species. Incorporating pumice or ground oyster shell will help amend the soil for better growing conditions. When planting penstemon in rock gardens, slopes and raised beds, you have the most ideal sites for many penstemon. Northern and alpine species are dependent on your soil preparation and the area’s precipitation.
Watering Requirements/Water Use
Overall, penstemons are “drought tolerant”. Soils that are well-drained are ideal because they will allow for root penetration. It is extremely important to match the soil type with the desired species to meet the appropriate water requirement. This recommendation needs to be applied regardless of the environment it is planted in. This is a general rule that needs to be applied whether you are growing penstemon in a container, trough or as an annual. Remember the hybrids bred for garden containers will need regular watering which means infrequent slow-trickle watering.
Test the soil moisture weekly by inserting a long screwdriver in the soil to check how far the soil moisture has traveled. Adjust watering needs based on recent precipitation. The watering requirement for penstemon depends on species such as the large-flowered hybrid species that requires some moisture but not be allowed to dry out completely. Avoid over watering these plants to avoid crown rot and decreased plant vigor.
Generally, fertilization is not required. Older and longer blooming plants may benefit from fertilization. However, do not use fertilizers high in nitrogen. Fertilize after the first flush of blooms.
To ensure the health of our penstemon, it is important to think about their care long after they are established. The large-flowered hybrids and bedding types need only dead-heading.
If more of these plants are desired, then leave the lower seed capsule to dry and reseed in the planting beds. Some penstemon species and hybrids will need to have their stems cut back after blooming. For many other species little pruning is needed. Winter protection is only necessary if the plants were not planted in the right place initially.