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 1/4-10 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 1/4-10
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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