The majority of penstemons thrive in full sun, but some prefer or tolerate sun for only part of the day or filtered sun. This has usually been mentioned in the descriptions. Where you live will have a great influence on how much light your penstemons receive. In high precipitation areas and those with many cloudy days, the greatest amount of sun exposure possible will produce plants that grow erect and with the brightest, clearest colors from the hybrids, midwestern and western species. Eastern species that are paler in color will grow well and show to good advantage in areas of partial shade. Choosing an area with good drainage and where air moves freely about the plants will also be beneficial, and you will probably not be troubled with diseases. Most penstemons are well able to withstand wind and rain damage and will not need staking if they have all the light they need. At high altitudes and in hot climates, many species that grow in full sun in their native locations often will bloom longer and fuller where they are shaded part of the day. There are a few tall-growing species such as Penstemon comarrhenus that do need full sun all day to develop strong stems that will not break off at the base when exposed to wind. Eastern species and hybrids will do well where they have only part-day sun exposure or filtered light. Hail will do little damage to any of the penstemons except the very large-flowered hybrids that have tender blooms and foliage. Many penstemons are secund and should be placed so that the flowers will face the sun and the viewer. Although many penstemon flowers are beautiful when backlit, particularly the reds and those that are glandular-hairy, most will be enjoyed where they face the viewer and the sun. Species that are quite open with medium or small, pale flowers are most effective against a dark background hedge, fence or wall.

Selecting, Growing and Caring for Penstemons
From Chapter 41

Lindgren, Dale and Wilde, Ellen. 2003. Growing Penstemons: Species, Cultivars and Hybrids: American Penstemon Society. 519 West Lancaster Avenue, Haverford, PA 19041-1413 : pp. 105-110