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 to early summer. The bright blue varieties are among the most popular, blooming in clear tones of blue and bluish-purple, offset by yellow centers.
Jacob's ladder is a hardy perennial plant. It is upright and clump-forming, but it will spread by seed. 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. 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.
- Botanical Name: Polemonium caeruleum
- Common Name: Jacob's ladder
- Plant Type: Perennial flower
- Mature Size: 12 to 24 inches tall and 12 to 15 inches wide
- Sun Exposure: Part shade
- Soil Type: Rich, well-drained
- Soil pH: 6.2 to 7.0
- Bloom Time: Spring, summer
- Flower Color: Purple, lavender, white, pink, yellow
- Hardiness Zones: 3, 4, 5, 6, 7, 8
- Native Area: Eastern North America
How to Grow Jacob's Ladder
Jacob's ladder will start blooming in late spring to early summer. The initial bloom will last two to four weeks, with flowers opening from the tops of the stalks down. After the bloom, deadhead the spent flowers to ensure repeat blooms. New plants are easy to grow from seed. Mature plants should be divided to prevent them from dying out in their centers. Jacob's ladder is relatively pest-free and low-maintenance, but it is particular about where it will grow.
Jacob's ladder plants prefer partial or dappled shade. Varieties with dark green leaves can handle more direct sun than the variegated varieties, as long as the soil is moist.
Plant Jacob's ladder in loose, rich, well-draining soil that can stay moist but not wet. It is more fussy about moisture than about soil pH but does best with a neutral soil pH of about 6.2 to 7.0.
Jacob's ladder plants that receive regular watering will bloom longer and remain attractive into summer. Water regularly to maintain medium moisture levels. Do not keep the soil wet. During dry periods, you may need to water more frequently to keep the plants lush.
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.
Divide mature Jacob's ladder plants 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.
In general, 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.
Jacob's ladder blooms about the same time as many alliums, bleeding heart, and Brunnera, and the colors are very complementary. 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 flowers
- Polemonium Bambino Blue: Beautiful light blue flowers
- Polemonium Snow and Sapphires: Variegated leaves and blue flowers; somewhat hardier than the similar Brise d'Anjou
- Polemonium Stairway to Heaven: Blue flowers on variegated foliage that blushes pink in cool weather
Growing From Seeds
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, then water. Keep the soil 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. The seeds take 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.
Common Pests and Diseases
Jacob's ladder plants are generally problem-free, but there are a few pests and diseases that will attack, particularly if 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: Control leafminers by removing affected leaves and/or by treating with neem oil.
- Slugs: Eliminate slugs with various homespun methods (such as tuna cans or eggshells) or apply an organic treatment (such as diatomaceous earth or a natural commercial repellent).
- Leaf spot: Prevent leaf spot by pruning to ensure good air circulation and watering in the morning so the foliage dries during the day.
- Powdery mildew: Control powdery mildew by keeping the foliage dry (water the ground, not the leaves), pruning for good air circulation, removing affected leaves (as practical), and applying a fungicide as needed.