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PENSTEMONS:  AN INTRODUCTION

Genus Penstemon  is a genus in the family Scophulariaceae and  is related to such plants as foxgloves, veronicas, diascias, cape fuchsias and even hebes.  The genus Penstemon  has approximately 270 species with many more subspecies.  All are found in North and Central America.   These include both herbaceous and evergreen species, many of which form attractive sub-shrubs.   Penstemons are characterized by their colorful tubular, sometimes bell-shaped, flowers.  Many are considered short-lived in the garden.

When Peter James and David Way prepared their The Gardener’s Guide to Growing Penstemons in 1998, they separated their book into two parts - Species Penstemons and Garden Penstemons.   We follow their precedent in these notes and begin with the species.

Avid hikers who have explored the  mountains of the West, the desert Southwest, the Great Plains or even the woods and meadows of the East Coast, might recall lovely vistas with patches of one species or another of penstemons accenting the landscape.  

The Species Penstemon are divided into various subgenera and sections which reflect the various adaptations the species have made to their environments and their pollinators.  Many of the species can be difficult to identify without the aid of a good guide.  There are many fine books on the species, including Penstemons by Robert Nold.  The American Penstemon Society also has a yearly bulletin and many useful resources to help amateur botanists identify penstemon in the field.  Membership is inexpensive and their yearly field trips are a wonderful way to meet fellow penstemon enthusiasts.

At Joy Creek Nursery, we have raised and killed scores of  species in our attempts to find plants suitable for our Pacific Northwest climate.  We have found many wonderful plants along the way that now brighten our gardens.  They include P.  pinifolius, P. cardinalis, P.  digitalis, P. heterophyllus, P. campanulatus, P. kunthii  and P. hirsutis.

We are especially interested in our own Northwest penstemon species many of which we have found to be temperamental in containers but successful in the garden.  What we have learned is that most of our natives thrive in difficult circumstances.  They resent fertilization.  They do not want any standing water around their crowns during our winter storms, although they have no objection to our local clay.

In order to accommodate these wonderful plants in our garden, we have modified rock gardening techniques to suit our purposes.  We have taken to adding ¼-10 gravel (made from our Northwest basalt) to our soils.  We top dress our dry-land beds with this gravel to wick standing water away from the root crowns of the penstemons.   Where we can, we grow our penstemons on a slope.  And, we grow them out in the open in full sun-light.

We especially admire P. cardwelli which is an evergreen sub-shrub creating a large mound of attractive leathery  foliage  This shrublet comes to vivid color in the spring when it is covered in violet blue tubular flowers.  Other sub-shrubs that we enjoy are P. fruticosa and its many forms and all selections of  P. davidsonii.  An imaginative gardener could have a whole dry-land garden that never looked withered in summer or devastated during the cold of winter by the skillful inclusion of these perennials.

Many of our native species form evergreen mats.  These can be employed as groundcovers.  Penstemon euglaucus and P. procerus are useful in this capacity. 

Among other outstanding  Northwest natives, our selection of P. serrulatus has turned out to be a very tough and colorful garden plant.  Its big cabbage-like leaves are stained burgundy during the winter.  In spring, spikes of purple blue flowers bring additional color to the plant.

The Garden Penstemons are often what gardeners think of when they hear the word penstemon.  These are the plants they see in mass plantings, sometimes even used as bedding plants in city parks.  These semi-evergreen perennials bloom from summer to fall bearing tall racemes of brilliant flowers.  They are the result of the complex crossing of many species.

As far as the Garden Penstemons are concerned, James and Way sorted them into three classifications that denote the sizes of the flowers:  small, medium and large.  They divided these classifications in turn into sub-classifications describing the shapes of the flowers: narrow, broad and (in the case of the large flowers) bell-flowered.  This is only one way to describe the Garden Penstemons but it is especially useful  for gardeners who are planning their gardens. 

We have found that another way to describe the Garden Penstemons is to measure the width of their foliage.  In general, our observations have led us to believe that the narrower the foliage the hardier and more long-lived the plants are for us.  For many years, the penstemons in our gardens had no trouble surviving our wet winters.  But recent weather patterns have brought more sudden and extreme early freezes and more rain.  Those penstemons with very wide foliage have been vulnerable to this weather and have tended to die or suffer severely.   Because we enjoy their brilliant flowers so much, we always replace them as needed.

The size of the foliage is directly related to the ancestry of the penstemon.  Those with narrower foliage and smaller flowers appear to have more influence from P. campanulatus and a few allied species which have proven undaunted by cold or wet in the Portland area.   It seems that the diminished surface area of the leaves protects the plants from the severity of freezing winds from the Columbia River Gorge.  The penstemons with broader leaves blacken in this kind of wind.  Their stems also display blackening and sometimes the plants die entirely.  Many times, however, the plants are only damaged and as soon as warmth returns to the Portland area, the remaining stems put on new growth.  As a rule of thumb, we prune our penstemon at the end of winter.  We cut out dead wood and cut back stems above a point where we see active growth.

Even with the Garden Penstemon, we use our modified rock gardening techniques.  We always make sure that the soil drains well and we often top-dress with an inch or so of ¼-10 gravel.  This trick really does increase the survivability of these penstemons.  We give them all as much sun-light as possible.  The Garden Penstemon do need occasional water in the summer to continue looking good, especially if they are intended to repeat bloom.  We cut spent bloom spikes back on a regular basis.  This stimulates the plants to produce more bloom spikes which helps continue the flower display well into the autumn.  Do not fertilize your Garden Penstemons.

Favorites among the large flowered forms include plants from an English series with bird names such as  P. ‘Raven’ and P. ‘Blackbird’.  Both have incredibly dark flowers that show up beautifully in contrast with the tawny tones of ornamental grasses.  Penstemon ‘Cherry Glow’ is breath-taking in its brilliant red flowers which rise up very tall flowering stems.

Penstemon  ‘Blue Midnight’ and P. ‘Garnet’ (‘Andenken an Friedrich Hahn’) are among the hardiest of the garden penstemons.  Their flowers are medium-sized, as are their leaves.  The iridescent flowers of P. ‘Mother of Pearl’ also fall in this category.

The small, inch-long flowers of P. ‘Evelyn’ represent the smallest flowers.  Echoing the small size of the flowers is the smaller size of the foliage.  As a result of this, ‘Evelyn’ has done very well in our dry border for more than a decade.

We have been lucky at Joy Creek Nursery to be able to introduce our own Garden Penstemon selections.  P. ‘Purple Tiger’, with medium-sized flowers, was the first and is still the hardiest of our introductions.  We have also released a series of large-flowered penstemons with vividly colored mouths and pure white throats which we call the Kissed Series.  The series includes P. ‘Violet Kissed’, P. ‘Coral Kissed’, P. ‘Cerise Kissed’ and P. ‘Wine Kissed’.  Our P. ‘Raspberry Flair’ and P. ‘Raspberry Wine’ have some of the largest flowers of all the garden hybrids.  In 2011, we introduced P. ‘Aurora’ which has large flowers of dark coral pink.

 

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