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How to Prune Rocky Mountain Penstemon

By Malia Marin ; Updated September 21, 2017

Native to dry woodlands, this relatively inconspicuous evergreen plant, with glossy narrow leaves, bears 18-inch stalks of deep blue-violet flowers each spring. Its beauty and drought tolerance has made this hardy jewel a classic component of water wise gardens. Like many other Southwestern natives, Rocky Mountain penstemon thrives on lean soils, modest amounts of water and little care. Too much pampering can actually cause weak growth and poor bloom. Proper early pruning will make plants bushier and produce more flowers. Pruning spent flower stalks will give your garden a manicured appearance.

Cut or pinch the tips of young plants in spring when the plant is well established, just above the second set of leaves on each stalk to encourage bushiness. Don’t cut the bottom rosette of leaves, just the tip ends of new stalks growing out of the base.

Trim off the spent flower stalks down to the base of the plant before the seeds ripen in summer to save energy in young Rocky Mountain penstemons. Sometimes this may even trigger a second bloom. You can also wait to trim the stalks until after the tiny black seeds fall away from the dry capsules so the plant can reseed.

Prune woody, older stalks from the base of the plant in late autumn to encourage new growth the following spring.

 

Things You Will Need

  • Sharp pruning shears

Tips

  • Allow seeds of older plants to mature and self sow to ensure a steady supply of these short-lived perennials in your garden.
  • Resist pruning a few plants in wilder parts of your garden to provide food and shelter for native birds and other animals over the winter.
  • Leave spent stalks over winter to shelter dormant plants if you live where winters are particularly cold and snowy.
  • You can safely mow Rocky Mountain penstemons planted in wildflower meadows down to a few inches in fall.
  • Plant Rocky Mountain penstemons in masses so that new, younger plants will hide older, woody ones for low maintenance spring color.
  • Combine Rocky Mountain penstemons with other native plants in mixed beds for a long blooming tapestry of colors and textures.
  • Don't spoil this plant with too much water or fertilizer. It will bloom best with lean, well drained soil and minimal irrigation.
  • You can use the attractive dried seed heads for craft projects.

Warning

  • Avoid pruning mature plants in early spring because this will interfere with flowering.

About the Author

 

Malia Marin is a landscape designer and freelance writer, specializing in sustainable design, native landscapes and environmental education. She holds a Masters in landscape architecture, and her professional experience includes designing parks, trails and residential landscapes. Marin has written numerous articles, over the past ten years, about landscape design for local newspapers.