Penstemon cobaea aka Cobaea Beardtongue

Penstemon cobaea belongs to the Plantaginaceae family. It is a perennial with soft, non-woody stems. Its common names include prairie beard-tongue and dew flower. It comes from the central United States to Arkansas. It grows in mild regions and forms leafy clumps. It is not native to Britain or Ireland. Its leaves fall when the growing season ends.

Garden plants grow about 1.6–3.3 feet (0.5–1 metre) tall and wide. The RHS also lists plants in bloom about 2 feet (0.6 metres) tall. Large, oval, green leaves sit below upright flower spikes. The leaves clasp the stems. The bell-shaped blooms range from white and pink to deep purple. Each spans about 0.08–0.25 feet (0.025–0.076 metres). Flowers open from spring into early summer. Missouri Botanical Garden lists May as the main bloom month. The blooms draw butterflies. NC State also lists the plant as a draw for pollinators.

Choose full sun, though the RHS allows some shade. Use sandy or loamy soil that drains well. The RHS lists neutral to alkaline soil as suitable. It favors rich soil that stays moist but drains well. Missouri Botanical Garden gives a dry-to-medium water range. It notes that the plant copes with drought and dry soil. It also copes with shallow, rocky ground. These sources suggest some range in water needs. They do not suggest that standing wetness suits the plant. Hardiness ratings are USDA zones 5–8 and RHS H6. The RHS advises dry winter mulch in cold areas.

Use it in sunny borders, rock gardens, or native plant beds. It also suits gravel gardens, prairie plantings, and wildflower meadows. The RHS lists pots, courtyard gardens, and wildlife gardens too. Tall flower spikes add height above the leafy clump. Missouri Botanical Garden says it needs little care and resists deer. Remove spent flower spikes to help prolong the bloom season. Cut stems back to low shoots in mid- to late March. Take softwood cuttings in early summer. Take semi-ripe cuttings in midsummer.

Missouri Botanical Garden reports no major pest or disease problems. Wet soil that drains poorly can still cause root rot. The RHS names powdery mildew as a possible disease. Aphids, slugs, and snails may cause trouble too. Chrysanthemum eelworm may also pose a problem. Soil must drain well even when the plant gets water regularly.