Common Name: Jacob's ladder
Type: Herbaceous perennial
Family: Polemoniaceae
Native Range: Northern Asia, Europe
Zone: 4 to 8
Height: 1.50 to 2.00 feet
Spread: 1.50 to 2.00 feet
Bloom Time: April to May
Bloom Description: Deep blue
Sun: Part shade to full shade
Water: Medium
Maintenance: Medium
Suggested Use: Naturalize
Flower: Showy
Tolerate: Deer, Heavy Shade
Culture
Grow in average, medium moisture, well-drained soils in part shade to full shade. Prefers rich, humusy, consistently moist soils. Soils must not be allowed to dry out. Best performance occurs in cool summer climates. Plants are intolerant of the high heat and humidity of summers in the deep South. Plants may be cut back to basal foliage after bloom to tidy the planting, to prevent any unwanted self-seeding and to encourage a possible late summer rebloom. Easily self-seeds in optimum growing conditions.
Noteworthy Characteristics
Polemonium caeruleum, commonly called Jacob’s ladder, is a generally erect, clump-forming perennial that typically forms a foliage mound to 18-24” tall and as wide. Odd-pinnate compound bright green leaves (to 27 leaflets each) appear ladder-like, hence the common name. Cup-shaped, deep blue flowers with contrasting yellow stamens appear in loose, drooping, terminal clusters (cymes) in spring (April-May in the St. Louis area).
Genus name comes from the Greek name polemonion originally applied to a medicinal plant associated with Polemon of Cappadocia.
Specific epithet means sky blue in reference to the flower color.
Problems
No serious insect or disease problems. Leaf spot and powdery mildew can be problems, particularly in humid climates. Foliage may scorch in too much sun. Leaflet tips will brown up if soils are allowed to dry out. Foliage will generally decline and become less attractive as the summer progresses. Watch for slugs.
Uses
Bright foliage and blue flowers will brighten shady locations in border fronts, rock gardens, woodland gardens, cottage gardens or shade gardens.