Penstemons, commonly referred to a beardtongue, are popular flowers in home gardens, as they bloom profusely from midsummer until frost and are available in a wide range of colours. Penstemon is large species that encompasses approximately 275 species. It is a perennial in Zones 8 to 10, but is grown as an annual in colder climates. Perennial penstemon requires moderate pruning to encourage lush new growth and abundant blooms.
Prune in spring once new growth appears--generally in April or May.
Examine the new shoots to determine if they are growing from the base of the plant or if they are growing on old wood from the prior year. Do not attempt to prune the plant unless you are sure if new growth grows on old wood or from the roots. If you can't tell for sure, wait until it is clear. Where new growth forms varies between species and determines how you prune the plant.
Cut old stems to the ground, if the new shoots are growing from the roots at ground level. This provides room for the new plant to grow and opens up the plant to sunlight and water.
Prune just above the lowest set of new leaves on plants where leaves form on old wood. This encourages the plant to send out side shoots and creates a compact, bushy plant.
Do not prune penstemon until you are sure if new growth occurs on old wood or from the roots.