When to Plant Penstemon: Spring or Fall Planting, Cold-Stratified Seed, Drainage and Deadheading Beardtongue

Penstemon, or beardtongue, is the largest genus of flowering plants native to North America, with 281 species by NC State's and Colorado State's count (MU Extension says about 270). The common name comes from a fifth, sterile stamen in each tubular flower, which is often hairy and looks like a tongue sticking out (NC State, MU Extension, UC Master Gardeners). Species range from 1-inch mats to 9-foot plants (NC State), and most bloom in spring and early summer, though some hybrids rebloom later (CSU). In the eastern U.S. the easiest native is tall white beardtongue, Penstemon digitalis, which NC State says grows 2 to 4 feet tall in Zones 3 to 8 and tolerates clay as long as it drains.

When to plant penstemon

Use our planting calendar to find your last spring frost for potted plants, or count back about 16 weeks from it if you want to chill seed indoors. The UC Master Gardeners note that some penstemons will not bloom until their second season, so a fall or early-spring start buys you flowers sooner.

How to plant penstemon

CSU calls rock gardens and xeriscapes ideal for many penstemons. In heavy soil, plant on a slight mound or in a raised bed so water drains away from the crown (our reading, based on the drainage warnings from CSU, MU Extension and the UC Master Gardeners).

Watering, feeding and deadheading

• Water sparingly once established. CSU says most are drought tolerant but even dry-land species need good spring moisture, and overwatering after flowering can cause crown rot. MU Extension waters infrequently.
• Skip fertilizer in the ground. CSU says most garden soils need none; feed only containers or cut-flower plants lightly. The RHS mulches border plants with compost each spring.
• Deadhead for more flowers (MU Extension, RHS, UC Master Gardeners). CSU says removing spent stalks before they set seed can lengthen a plant's life.
• Or let some seed ripen. Leave a few stalks in fall if you want seedlings or seed for birds (CSU, UC Master Gardeners, NC State).
• Prune in spring. The UC Master Gardeners cut back by about a third in March; the RHS cuts border hybrids back by a third in fall and then to just above the lowest new shoots in April or May.

Penstemon in containers

CSU recommends long-flowering, compact hybrids for pots, such as the 'Twizzle' series, 'Red Riding Hood' and 'Prairie Twilight', and names P. heterophyllus and P. × mexicali among good container choices. The RHS uses a gritty mix (about 30 percent grit by volume), waters until it runs out of the drainage hole and then waits until the top inch is dry, feeds with a balanced fertilizer in spring and wraps pots if more than a day or two of freezing weather is forecast.

Fall and winter

• Plant early enough that roots establish before winter; in Missouri, divide in spring or fall (MU Extension).
• Keep the crown dry. The RHS says alpine kinds especially dislike winter wet; CSU and MU Extension link wet soil to root and crown rot.
• Replace old plants. The RHS says penstemons often need replacing after about five years as they get woody, so keep a few cuttings or seedlings coming.

Pests and problems

Penstemons are generally trouble-free (CSU, MU Extension, RHS), and NC State lists no serious pests for P. digitalis. CSU names grasshoppers, flea beetle larvae, seed bugs, leaf spot and rust, and says plants that suddenly collapse in wet soil usually have root or crown rot; don't replant penstemon in the same spot. The RHS mentions powdery mildew and frost damage, and MU Extension says tall species such as P. digitalis can flop in wind and heavy rain. The UC Master Gardeners call penstemons deer resistant.

Penstemon around the vegetable garden

CSU says most penstemons draw pollinators, especially solitary bees; NC State notes that the genus supports a specialized native bee; and MU Extension says firecracker penstemon attracts hummingbirds. A clump at the sunny, dry corner of the plot brings bees in early summer (our reading). See flowers that attract beneficial insects. Good neighbors with the same lean, well-drained needs include yarrow, salvia, catmint and Russian sage.

Frequently asked questions

When is the best time to plant penstemon?

In most of the U.S., in spring after the last frost (MU Extension). In hot, dry-summer climates, fall is best and early spring second best; avoid midsummer (UC Master Gardeners).

Can I plant penstemon in fall?

Yes, early enough for roots to establish. The RHS plants container-grown plants through October if the soil stays moist, and the UC Master Gardeners prefer fall in California's Central Valley.

How do I grow penstemon from seed?

Most need a cold, moist period. Sow outdoors in fall or early winter, no more than 1/2 inch deep (MU Extension, UC Master Gardeners), or chill sown pots in the refrigerator for about 112 days before warming them (MU Extension).

Why did my penstemon die?

Usually wet soil. CSU, MU Extension and the UC Master Gardeners say overwatering or poor drainage causes root and crown rot. Penstemons are also short-lived, about 3 to 4 years (UC Master Gardeners).

Should I deadhead penstemon?

Yes, for more flowers (MU Extension, RHS). CSU says removing spent stalks before they set seed can extend a plant's life; leave a few in fall if you want seedlings.

Does penstemon need fertilizer?

Not in most garden soils (CSU). MU Extension keeps fertility low; feed container plants lightly in spring (RHS, CSU).