Penstemons are a 'must have' for hassle-free colour in summer gardens

Penstemon 'Electric Blue' Picture courtesy Ball StraathofPenstemon 'Electric Blue' Picture courtesy Ball StraathofNot many perennials are hardy, water-wise, long flowering, and can also grow in full sun or semi-shade. Penstemons can and are available in many gorgeous flower colours, and in all sizes. Read more about growing and caring for them.

Penstemon is also called “beard-tongue” but in South Africa we know them simply as penstemons. This genus belongs to the mint order (Lamiales), containing about 250 species of perennials and sub-shrubs native to North America, particularly the western United States. Some grow on high mountains or in forest glades, while others thrive in the desert, foothills or plains. And, although they are among the most attractive native flowers of North America, Europe has always been more active in their cultivation, and hundreds of beautiful garden hybrids have been developed there since the early 19th century.

Penstemon Hartwegii Arabesque 'Violet' Picture courtesy Ball Straathof Penstemon Hartwegii Arabesque 'Violet' Picture courtesy Ball Straathof In early summer, right after your spring bloomers have faded, they will spring up and quickly fill your garden with their beautiful spires of foxglove-like flowers which come in hues to suit every colour palette. Flowering will continue sporadically throughout summer and into autumn, and in coastal gardens the flowers can appear all year round, making penstemons a 'must have' for hassle free summer gardens.

The large bell-shaped flowers are produced in loose spikes at the ends of tall stems and they come in hues ranging from white to soft pinks, through salmon and peach to deep rose, lavender to dark purple, and also in bold fiery reds to electrifying blues. Some varieties also have distinctive veining and white throats. Penstomon is related to foxgloves and snapdragons, a kinship evident in the vertical flower spikes and the flared, tubular blooms The shape of the flowers will attract nectar eating birds to the garden, as well as butterflies and bees.

The various cultivars also come in many shapes and sizes, from dwarf varieties which you can tuck into rock gardens, to larger plants that bring colour and movement to the back of the flower border. The shape and colour of the leaves also varies, depending on the cultivar, and can be oval, lance-shaped or needle-like, with colours ranging from green or blue-green, to a delightful deep purple.

In the Garden:

Visit your local garden centre to find these beauties in full bloom – they will also stock the best varieties suited to your region. The garden hybrids sold today are very floriferous and are compact, bushy plants which vary in height from short to tall, making them perfect for gardens large or small.

Penstemon Hartwegii Arabesque 'Appleblossom' Picture courtesy Ball Straathof Penstemon Hartwegii Arabesque 'Appleblossom' Picture courtesy Ball Straathof They are indispensable if you want colour in xeriscape and water-wise gardens. The smaller types are ideal in rockeries and the taller growing ones look spectacular when planted next to boulders. In wild meadow and cottage style gardens they are the backbone of mixed perennial borders, with the dwarf ones in front and the taller ones at the back of the bed.

All cut flower gardens need a couple, and for tiny gardens the dwarf varieties are quite delightful and easy to grow in pots. Planted close to fruit trees or vegetable gardens they will not only attract essential pollinators, but will also greatly beautify the area.

Because of their tubular nectar-rich flowers, they are one of the best exotic garden perennials for attracting sunbirds to the garden, not to mention bees, butterflies and other pollinators.

Cultivation/Propagation:

Penstemons are easy to grow in full sun or semi-shade. In coastal regions they thrive in full sun, but in hot inland gardens the plants will appreciate some shade during the hottest time of the day. Varieties with purple or reddish leaves will exhibit the best foliage colour when grown in more direct sunlight.

Although penstemons will adapt to most well-drained garden soils, they do best in slightly alkaline soil, and will even grow in soils that are mostly sand or gravel.  When planting, avoid using soil amendments that hold moisture, such as peat moss and manure. They are extremely sensitive to heavy or poorly draining soils, so if your soil is not perfect try planting them in raised beds or pots. Beds on a slope will allow water runoff, allowing them survive wetter conditions.

Penstemon Hartwegii Arabesque 'Red' Picture courtesy Ball Straathof Penstemon Hartwegii Arabesque 'Red' Picture courtesy Ball Straathof These perennials are water-wise and many of the species even grow well in desert-like climates. They dislike excessive winter moisture and in the winter rainfall regions they are best planted as summer annuals, or in pots which can be moved under cover during the wet months.

The amount of water you will need to give them in the garden will depend on the water-holding capacity of your soil, and because most garden soils tend to be quite fertile, once the plants are established it may not be necessary to water or feed at all.

Garden Hybrids, however, are not as drought tolerant as native North American species, and to keep them looking at their best in the garden they may require moderate watering during prolonged hot and dry spells. Ideally, during the growing season the plants’ crowns should remain dry while the roots should have access to a small but steady supply of moisture.

It is not necessary to feed the plants, but a little general purpose fertiliser, applied occasionally during the growing season, will do no harm, and potted specimens respond well to a little feeding.

Penstemons are hardy to moderate frost if they are kept dry in winter, going dormant and re-shooting again in spring.

To encourage re-blooming, pinch the plants back after the first flush of blooms in spring. And to keep them flowering into autumn, cut the faded flower stems back to side shoots in mid to late summer.  In milder climates where the plants remain evergreen, cut them back hard in late winter to encourage a new flush of dense growth in spring.

Deadheading will also prolong flowering, but be sure to leave a few seed heads on the stalks toward the end of the season so your plants can reseed.

While extremely showy through their lifespan penstmons are relatively short lived and will need replacing every 3 to 4 years.

They are propagated from root division in late winter or early spring, or by seeds sown in autumn. Softwood cuttings of nonflowering shoots root easily, and can be taken in mid-summer to late summer.

Penstemon Hartwegii Arabesque 'Orchid' Picture courtesy Ball Straathof Penstemon Hartwegii Arabesque 'Orchid' Picture courtesy Ball Straathof Problems, Pests & Diseases:

Although there are no serious threats, watch for root rot in heavy, poorly draining soils. Leaf spot, rust, powdery mildew, and blight can also occur. Penstemons may be bothered by slugs, snails, and spider mites.

Toxicity:

Toxic Principle: May accumulate selenium if growing in selenium-rich soils.

Although we could not find Penstemon listed as toxic to pets, there is information online that Penstemon does accumulate Selenium, and additional information indicates that an excess of Selenium is not healthy for pets. So it would be wise to keep your dogs and cats away from Penstemon if you can, and it is always wise to supervise young children in the garden.

There are also reports that Penstemon affects horses and ruminants. Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. Horses, in particular, may become severely lame. Initially, circular ridges form in all feet, and as the hoof wall grows out, the ridges may crack and lames can be severe due to lamimitis and even sloughing of the hoof wall.

It seems that Penstemons are rarely a problem to livestock themselves, but as faculutative selenium accumulators, serve to indicate the potential for other forages high in selenium.

If you are concerned about toxic plants it is always advised that you do your own research before planting.