Penstemon is a large genus of flowering perennial plants with many different species. Most species of penstemon have similar germination requirements. But because the genus is so large, there are a few outliers with different requirements. While these instructions are general guidelines, research your specific variety of penstemon for specific requirements.
A Cold Period
Penstemon needs cold temperatures to germinate. If you live in an area where the temperature falls below freezing for at least 60 days in winter, then sow the seeds outside in December. If your climate is warmer, place moistened vermiculite in a plastic bag, mix in the seeds then store the bag in the refrigerator for 12 weeks before planting them outdoors in early spring.
Water the soil for Penstemon seeds so that it is moist a few inches below the seedlings immediately after planting. Then check the soil's moisture level daily with your finger to make sure it remains moist while the seeds are germinating. Continue watering the area, only as needed.
Light and Oxygen
Most penstemon seeds should be planted shallow, to provide access to light and oxygen while they are germinating. Small penstemon seeds (like firecracker penstemon seeds) should be sown on the surface of the soil or covered with a thin layer of soil. Larger penstemon seeds (like 'Bandera' Rocky Mountain penstemon seeds) should be planted 1/4 inch deep. Research your penstemon species for specific sowing depths for your seeds.
After a period of cold (in the ground or in the refrigerator), your penstemon seeds should germinate within 4 to 8 weeks (depending on the species). However, some species of penstemon are tougher to germinate. If your seeds have not sprouted by May, they may need to spend another season or two underground before conditions are right for germination.