Also known as beard tongue, the penstemon plant is a popular selection for gardeners for its wide array of colours and the ability of various varieties to grow in different climates and terrains. In the proper conditions, the plant, with its tubular bell-shaped flowers, should grow with no problem. To enhance the plant's appearance, you should cut it back periodically to encourage a more full, compact growth and more flowers.
Mix a very mild solution of bleach in water in a small bucket, about one part bleach to nine parts water or a little more. The solution is for the sterilisation of your pruners, to prevent bacteria and other microbes from invading the cuts you are about to make to your penstemon.
Sterilise your pruners by dipping the blades into the mild bleach solution. Wipe the blades dry with a small cloth.
Cut back your penstemon plants using your pruners. Plants should be cut back until they are just about five or six inches from the ground. Small penstemon plants--those that grow to about four inches--can be pruned to about two inches from the ground.
Remove old stems. As you are going through your penstemon plants, note where there are new shoots and cut out old stems as close to the base of the plant as you can.
Penstemon should be cut back in the spring, after the last frost. Cutting them back at that time encourages growth, blooms in the summer and fall, and prevents them from getting floppy as they grow. Avoid pruning your penstemon in the late summer or fall, as they will need the growth to protect them in the cold winter months. If you do not see any new growth as you are pruning your penstemon, either it has not yet sprouted, or it may be a sign that your penstemon is nearing the end of its life. Either way, just cut the stems back but do not remove them entirely. Check again in a couple of weeks for any new growth. After cutting back your penstemon plants, make sure the surrounding area is weed free to prevent invasive plants from competing with your penstemon for space, nutrients, water and sunlight.
Use caution when dealing with any sharp instrument, like pruners. Keep them sharp to make pruning easier and to prevent slips and accidents. Wear gloves for protection.