Jacob's ladder (Polemonium) was given its common name because the arrangement of its leaves is somewhat ladder-like. However, it's Jacob's ladders' flowers that are the real attraction. Polemonium caeruleum and its cultivars send up clusters of flowers atop long stems in late spring/early summer. The bright blue varieties are among the most popular, blooming in clear tones of blue and bluish-purple, offset by yellow centers.
Although Jacob's ladder plants are relatively pest free and low maintenance, they are particular about where they will grow. But if you have the right conditions, as described below, Jacob's ladder is lovely.
Overview and Description
Jacob's ladder is a hardy perennial plant. It is upright and clump-forming, but it will spread by seed.
- Botanical Name: Polemonium caeruleum and cultivars
- Flowers: Most Jacob's ladder plants have bell-shaped flowers in shades of purple and lavender, but there are also white, pink and yellow varieties available, although harder to find. Jacob's ladder will start blooming in late spring/early summer. The initial bloom will last two to four weeks, with flowers opening from the tops of the stalks down. Deadhead the spent flowers for repeat blooms.
- Leaves: The compound leaves are composed of rows of narrow, pinnate leaflets. The branches grow from a basal rosette and arch and sway as they grow tall.
- Mature Size: This will depend on which Polemonium you are growing, but in general, the plants will reach 12 to 24 inches in height and 12 to 15 inches in width.
- USDA Hardiness Zones: Hardiness depends on the variety you are growing and your growing conditions, but most Jacob's ladder plants are reliably perennial in USDA Hardiness Zones 3 to 8.
Jacob's ladder blooms about the same time as many alliums, bleeding heart, and Brunnera and the colors are very complimentary. The delicate swaying branches of Jacob's ladder plants are a nice contrast to the more substantial leaves of Brunnera as well as hosta leaves that may still be unfurling as Jacob's ladder blooms.
Look for these kinds of Jacob's ladder for your garden:
- Polemonium Album: White flowering
- Polemonium Bambino Blue: Beautiful light blue flowers.
- Polemonium Snow and Sapphires: Variegated leaves and blue flowers. Somewhat hardier than the similar Brise d'Anjou (24 to 30 inch tall, suitable for zones 5 to 8)
- Polemonium Stairway to Heaven: Blue flowers on variegated foliage that blushes pink in cool weather. (12 to 24 inches tall. Zones 4 to 8)
Jacob's ladder can be grown from seed or from division:
- Starting Jacob's Ladder Seed: If you already have a Jacob's ladder plant, it will self-seed on its own. You could also collect seed to replant elsewhere. 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 two months before your last frost date to transplant in spring or sow in mid-summer to transplant in the fall. Seed takes up to a month to germinate and should be kept moist until then. Transplant outdoors in spring, just before your last frost date, or in early to mid-fall.
- Dividing Jacob's Ladder Plants: Jacob's ladder plants should be divided every two to four 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.
Soil: Jacob's ladder is more fussy about moisture than about soil pH, but they will grow best in a loose, rich soil with a neutral soil pH of about 6.2 to 7.0.
Exposure: Jacob's ladder plants prefer partial or dappled shade and a moist, but well-draining soil. Varieties with dark green leaves can handle more direct sun than the variegated varieties if the soil is moist. Plants that receive regular watering will bloom longer and remain attractive into summer. Jacob's ladder prefers moist, but not wet, soil.
Maintenance: Jacob's ladder requires minimal maintenance. 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 will replace the trimmed foliage.
Feeding: 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. Feed them again once the faded flowers have been cut back.
Pests and 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. Other potential problems include leafminers, slugs, leaf spot, and powdery mildew. They are also apparently delicious to groundhogs.