Penstemon ‘Sour Grapes’ – This RHS Award of Garden Merit winner features magenta-blue flowers with white throats and deep purple striping. These are borne from early summer to autumn over lance-shaped mid green foliage. Penstemon prefer part to full sun, with well-drained soil and are much favoured by hummingbirds. Grows 24″ high by 18″ wide. Zone 7.
Penstemon ‘Rich Ruby’ – A very large-flowered cultivar with foxglove-like blooms of a deep ruby red with darker throats and contrasting white stamens. You need to be careful not to over-fertilize Penstemon as this can lead to lush growth which is prone to winter dieback. Eventually forms large multi-stem clumps. Grows 22-30″ high by 18″ wide. Hardy to zone 7.
Penstemon heterophyllus ‘Margarita BOP’ – This Penstemon was discovered at Los Pilitas Nursery in California and features unusual flowers of a clear sky blue blended with violet (the two-tone effect reminds me of some Pulmonaria) that fade to purple – these emerge from yellow-tinted buds. Probably a hybrid with P. laetus. Grows 24″ high by 18″ wide. Hardy to zone 6.
Penstemon ‘Garnet’ (syn. ‘Andenken an Friedrich Hahn’) – A long-lived Penstemon with pendulous deep reddish-pink flowers that appear from July through to October. It is named after an 18th century German astronomer and is considered to be a P. campanulatus hybrid. Cut back in spring when new growth appears at the base. Grows 18-24″ high by 18″ wide. Zone 7.
Penstemon ‘Prairie Dusk’ – This cold hardy hybrid was developed in Nebraska and features rosy-purple flowers with white throats borne from May to August. It is a cross of Penstemon barbatus ‘Flathead Lake’ and Penstemon strictus and is quite drought once established. This is a good perennial to draw hummingbirds into your garden. Grows 2′ high by 12-18″ wide. Hardy to zone 3.