Jacob's ladder (Polemonium caeruleum) is a clump-forming perennial that earned its common name due to the rung-like arrangement of its pinnate, light green leaves. However, it is the flowers of Jacob's ladder that are the real attraction. The species form and its various cultivars send up clusters of flowers atop long stems in mid- to late spring. Most varieties have delicate bell-shaped flowers in shades of purple and lavender, but there are also white, pink, and yellow varieties available. The bright blue or purple varieties are among the most popular, blooming in clear tones offset by yellow centers. The delicate foliage and the fluorescent color of the flowers make Jacob's ladder a favorite for shady areas.
|Botanical Name||Polemonium caeruleum|
|Common Name||Jacob's ladder|
|Plant Type||Herbaceous perennial flower|
|Mature Size||12 to 24 inches tall; 12- to 24-inches spread|
|Sun Exposure||Part shade to full shade|
|Soil Type||Rich, well-drained|
|Soil pH||6.2 to 7.0 (acidic to neutral)|
|Bloom Time||Spring, summer|
|Flower Color||Mostly blue and purple; white, pink, and yellow cultivars also available|
|Hardiness Zones||3 to 8 (USDA)|
|Native Areas||Northern Asia, Europe; has naturalized in Eastern North America|
How to Grow Jacob's Ladder Plants
Jacob's ladder thrives in USDA Zones 4 to 9 reaching a height of about 30 inches and spread of 2 feet. This woodland type wildflower grows well in average well-drained soil in shady locations where few flowering plants thrive, provided the soil is kept consistently moist. This can be a slightly temperamental garden plant, reacting badly to soil that is too dry or too wet, or to a climate that is too hot or too humid. Jacob's ladder usually starts blooming in mid-spring, sometimes continuing into early summer. Deadheading spent flowers may prompt a second bloom period.
These plants are easy to grow from seed and they will very easily self-seed and spread in an uncontrolled fashion in the garden unless the spent flowers are removed before seeds can fall.
Jacob's ladder plants prefer partial or dappled shade. Varieties with dark green leaves can handle more direct sun than the variegated varieties, so long as the soil is kept consistently moist.
Plant Jacob's ladder in loose, rich, well-draining soil that will remain moist but not wet. It is more fussy about moisture than about soil pH but does best with a relatively neutral or slightly acidic soil pH.
Jacob's ladder plants that receive regular watering will bloom longer and remain attractive into summer. Water regularly to maintain medium moisture levels, but avoid soggy conditions. During dry periods, you may need to water more frequently to keep the plants lush.
Temperature and Humidity
Jacob's ladder prefers a relatively cool summer climate, and it can succumb to high heat in warm southern gardens. Very humid conditions can bring on leaf spot fungal diseases or powdery mildew.
Polemonium caeruleum is a long-lived perennial in the right conditions and if it is fed properly. 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.
Propagating Jacob's Ladder
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.
Growing From Seeds
If you already have a Jacob's ladder plant, it will self-seed on its own from seeds dropped from flower heads. You can also collect the seeds 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 two months before your last frost date if you want to transplant in spring, or sow in mid-summer if you want 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.
In general, Jacob's ladder requires minimal maintenance. Once the flowers finish blooming, cut the flower stalks back to the plant's base to encourage repeat blooms. If the foliage starts to look tattered, it can also be cut back and cleaned up. New growth will replace the trimmed foliage.
Comparison With Creeping Jacob's Ladder
A closely related plant is Pelamonium reptans (creeping Jacob's ladder), a native wildflower of eastern North America. Also known as Greek valerian, creeping Jacob's ladder has a similar appearance to P. caeruleum, but it is somewhat shorter and even more tolerant of cool conditions. It is a short-lived perennial, however, often behaving as a biennial. The native species is rarely planted in gardens, but there are some good cultivated varieties available, including 'Blue Pearl' and 'Brise d'Anjou'. Despite the name, this plant does not spread by creeping rhizomes, but it does spread readily by self-seeding.
Varieties of Jacob's Ladder
Look for these kinds of Jacob's ladder for your garden:
- Polemonium caeruleum' Album' has white flowers.
- P. caeruleum 'Bambino Blue' features beautiful light blue flowers.
- P. caeruleum 'Snow and Sapphires' has variegated leaves and blue flowers; it is somewhat hardier than the similar Brise d'Anjou.
- P. reptans 'Stairway to Heaven' exhibits blue flowers on variegated foliage that blushes pink in cool weather.
Common Pests/ 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.
Polemonium caeruleum. Missouri Botanical Garden.
Rooney-Latham, S. & Bischoff, Joseph. First Report of Powdery Mildew Caused by Podosphaera euphorbiae-hirtae on Euphorbia tithymaloides in California. Plant Disease. 96. 1822, 2012. doi:10.1094/PDIS-05-12-0461-PDN