The following directions apply to gardeners in difficult climates such as high altitudes where the sun is strong and where temperatures and climate conditions can vary from mild to freezing any day in the planting seasons. Those in gentler climates can probably plant young plants directly in the garden and shelter them from direct sun for a week to ten days, water regularly for the first growing season, and have great success. When you have small plants from nurseries, prepare a soil mix that is similar to your garden soil but enriched with some compost, loosened with sand and moistened. Remove plants from their containers one at a time and wash the potting soil away by swishing in a bucket of water, or shaking it off if the roots are not too tangled, until the roots are bare. Separate the roots and spread over some of your soil mix in a larger pot. Firm additional soil mix among and over the roots and up to where stems break from the crown. Water with a transplant solution and set the plants in a location where they are protected from strong winds and sun. If they have just come from a coldframe or greenhouse they may also need protection from cold. Gradually expose them to outdoor conditions when it is mild. If they need watering again, set them in a tray of water only until the top of the pot shows moisture. Remove from the water tray. After two or three weeks they will be ready to set into prepared holes in the ground to which a small amount of slow-release fertilizer has been added. Be sure the crown is in the soil but not buried. Firm the soil around the crown and water with transplant solution to settle soil around the roots. Add more soil if the crown is exposed after the plant has been watered in. An up-ended basket or translucent row cover will be needed for several days after plants have been set out in case weather conditions suddenly become harsh.

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