Jacob's Ladder (Polemonium)
dJacob's Ladder (Polemonium caeruleum) and cultivars
Type: Perennial Hardiness Zones 3–8. Bloom Time: late spring/early summer. Height: 12 -24 in (h) Spread: 12 - 15 in Exposure: Shade to partial shade. Moist, but not wet, soil.
Soil/pH/Water: Jacob's Ladder is more fussy about moisture than about soil pH, but they will grow best in a loose, rich, well-draining soil with a neutral soil pH of about 6.2 - 7.0. Plants that receive regular watering will bloom longer and remain attractive into summer.
Maintenance: Jacob's Ladder requires minimal maintenance. The initial bloom will last 2--4 weeks, with flowers opening from the tops of the stalks down. Once the flowers finish blooming, cut the flower stalks back to the plant's base. You should get repeat blooms. If the foliage starts to look tattered, it too can be cut back and cleaned up. New growth should replace the trimmed foliage.
Fertilizing: Jacob's Ladder is a long-lived perennial. Give the plants a boost in early spring with a dose of balanced fertilizer, as the new growth is emerging. Once the faded flowers have been cut back, they can be fed again to encourage repeat blooming.
Pests & Diseases: Jacob's Ladder plants are generally problem free, but there are a few pests and diseases that will attack, particularly is the plants are stressed. The most common problems are sun scorch and insufficient water, which cause the leaf tips to start browning. Varieties with dark green leaves can handle more direct sun than the variegated varieties, if the soil is moist. Other potential problems include: Leafminers, slugs, leaf spot and powdery mildew. They are also apparently delicious to grounghogs.
Propogation/Transplanting: Jacob's Ladder can be grown from seed or from division. Plants should be divided every 2 - 4 years, or they will start to die out in the center. They divide most easily and successfully in early spring. Carefully lift and separate the basal rosettes, replant and water well.
Starting Jacob's Ladder Seed: If you already have a Jacob's Ladder plant, it will self-seed on its own. Jacob's Ladder can be direct seeded in either spring or fall. Loosely cover the seed with soil, water and keep moist and be sure to mark the spot so that you do not disturb it. To start seed indoors, sow either 2 months before your last frost date or in mid-summer, to transplant in the fall. Seed takes up to a month to germinate and should be keep moist until then. Transplant outdoors in spring, just before your last frost date, or in early to mid-fall.