Swollen penstemon or penstemon rydbergii as it is known botanically, is a flowering perennial herb or small shrub. It produces small lavender blue flowers in late spring and summer and grows from a semi-woody clumping rhizome. Swollen penstemon grows in moist soil in open undisturbed lands including meadows and gentle hillsides. It is widely naturalized in the western United States and requires little pruning unless damaged or a need to control its sprawl or size.
Trim swollen penstemon to remove dead stems, damaged or diseased foliage as you see it throughout the growing season. Secateurs work well as do loppers. Cuttings should be cleaned up from the soil to prevent disease from taking hold.
Cut swollen penstemon down to size once a year or as needed in the late summer after bloom to control its shape, size and spread in the garden.
Shear down swollen penstemon top foliage in the early winter or early spring in climates where it does not survive the winter. Remove foliage early enough in the spring after the last hard frost to make room for new growth.