March or April would be too late to plant penstemon seeds in the Sierra Nevada. The ground is often not accessible that time of year because of all the snow we get. In April, we can get very snowy weather followed by temperatures warm enough to dry the soil out significantly.

I have had the best results planting containers in the ground from June through October. In the spring or late fall, smaller plants can heave out of the ground from the frosts we get. I live across the street from a meadow, in a cold micro climate. We typically get below freezing nighttime temperatures until mid-June. Mulching heavily can help prevent frost heave, but dry-growing penstemons tend not to like lots of material around their stems.

Thanks for commenting.