From the Greek pente, five, and stemon, stamen, about the five stamens (Scrophulariaceae). This genus of over 250 species of hardy and half-hardy herbaceous annuals, perennials, and sub-shrubs is almost exclusively North American. The name is sometimes erroneously spelled Pentstemon. Though many are grown in British gardens, some species do not thrive, and it seems likely that the continental climate, with its colder winters and hotter summers, needs to make these plants happy.
The very popular late summer bedding penstemons were derived from an initial crossing of P. cobaea and P. hartwegii, and they have a reasonably wide color range from pinks and reds to deep maroons and purples. P. heterophyllus is a fine sub-shrub with blue flowers which usually attract interest when well grown. Another striking plant is the herbaceous P. barbatus (syn. Chelone barbata), a tall grower up to 3 feet, with bright vermilion-scarlet flowers.
Types of Penstemon
- P. angustifolius, 1 foot, soft blue, July, western United States.
- P. antirrhinoides, 3 feet, lemon-yellow, July, California.
- P. azureus, 1 foot, blue, August, North America.
- P. barbatus, 3 feet, scarlet, summer, Colorado.
- P. barrettiae, 1 foot, bright violet, May—June, western United States.
- P. bridgesii, 2 feet, scarlet, July to September, North America.
- P. campanulatus, 2 feet, rosy-purple, violet or white, June, Mexico and Guatemala.
- P. centranthifolius, 3 feet, scarlet, summer, California and western Arizona. P. cobaea, 2 feet, purple or white, August, United States.
- P. confertus, 1 foot, purple and blue, summer, Rocky Mountains.
- P. cordifolius, 4 feet, scarlet, summer, partial climber, southern California.
- P. davidsonii, 1-2 inches, ruby-red, summer, spreads by underground stems, rock garden. California.
- P. diffusus, 2 feet, blue or purple, September, western North America.
- P. fruticosus, 9-12 inches, purple, summer, north-western United States; var. crassifolius, with minor leaf differences.
- P. glaber, 2 feet, purple, July, United States.
- P. glaucus, 15 inches, purple, July, Rocky Mountains.
- P. hartwegii, 2 feet, scarlet, summer, Mexico.
- P. heterophyllus, 1-3 feet, sky blue, July, California.
- P. hirsutus (syn. P. pubescens latifolius), purple or violet, 1-3 feet, July, United States.
- P. isophyllus, sub-shrubby, 4-5 feet, crimson-scarlet, white within, late summer, Mexico.
- P. laevigatus, 3 feet, white or pink, summer, United States.
- P. menziesii, 6 inches, purple, June, northwestern America.
- P. ovatus, 2 feet, blue to purple, August to October, United States.
- P. richardsonii, 2 feet, violet, summer, United States.
- P. rupicola, 4 inches, ruby, northwestern America.
- P. scouleri, 1i feet, purple, May to June, United States.
- P. spectabilis, 4 feet, rosy-purple, summer, Mexico and southern California.
New types Penstemon
The following are some suitable modern varieties:
- ‘Blue Gem’, azure-blue, summer;
- ‘Chester Scarlet’, summer;
- ‘Evelyn’, pink, May—October;
- ‘Garnet’, wine-red;
- ‘George Home’, summer;
- ‘Newberry Gem’, pillar-box red;
- ‘Six Hills Hybrid’, rosy-lilac, May—June.
How to plant and grow Penstemon
A rich, slightly acid soil or compost mixture of 1 part leaf mold or peat and two parts good loam is most suitable. A sunny aspect is required. The summer bedding penstemons need weekly watering with a soluble fertilizer or liquid manure to keep them growing and flowering well. Seed is available for many species. This should be sown under glass in February or March at a temperature of 55-65°F (10-18°C), and the young plants are set out in May after they have been hardened off. However, to get similar hybrid plants precisely, it is necessary to take cuttings and raise them under glass in August. They should not be disturbed till the following April. Plants may also be divided in April.