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Polemonium caeruleum Blue Pearl seeds - Jacob's ladder

Polemonium caeruleum Blue Pearl
Jacob's Ladder, Greek Valerian

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This Polemonium is a compact perennial with azure blue flowers borne in terminal clusters. Valued for its finely divided foliage and spring flowering, this variety thrives in humus-bearing, moist, but well-drained soils. Hardy down to -20 °C, it prefers partially shaded positions. Sow indoors 6 to 8 weeks before the last frosts, or directly in situ in spring.
Flower size
2 cm
Height at maturity
45 cm
Exposure
Sun, Partial shade
Germination time (days)
25 days
Sowing method
Sowing under cover
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Sowing period February to April
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Flowering time May to July
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Description

Polemonium caeruleum 'Blue Pearl' is a compact variety of Jacob's Ladder, also known as Greek Valerian, remarkable for its azure blue spring flowering. This bushy perennial has charming, finely divided foliage, similar to that of ferns. In borders, naturalistic gardens, or partially shaded areas, it appreciates moist, well-drained soil. This soft, poetic blue polemonium is robust, easy to grow and undemanding.

Polemonium caeruleum 'Blue Pearl' belongs to the Polemoniaceae family. Native to temperate regions of Europe and Asia, the species is naturally found in damp meadows, forest edges and mountainous areas.
The 'Blue Pearl' cultivar was selected for its abundant flowering and reduced size. This plant reaches a height of 30 to 60 cm and spreads 30 to 45 cm wide. It has a bushy and supple habit. The growth is moderate and flowering generally occurs from the second year after sowing. The upright stems bear clusters of campanulate azure blue flowers at their tips, measuring about 2.5 cm in diameter, with a light centre and yellow anthers. The flowering extends from May to June, sometimes until July, depending on the climate. The foliage is deciduous; it disappears in winter and re-emerges from the ground the following spring. It is compound with alternate, pinnate leaves, with bright green, oblong leaflets.
Polemonium 'Blue Pearl' is hardy down to -20°c but does not tolerate periods of prolonged drought or intense summer heat. The plant can self-seed spontaneously and is easily divided in spring.

The blue polemonium 'Blue Pearl' proves to be an excellent perennial for the damp, natural corners of the garden. More compact than the 'Lambrook Mauve’ variety, it fits well in the front or heart of beds, at the foot of old-fashioned roses or on the edge of light woodland. Perfect in mixed borders or in naturalistic garden scenes, it harmonises beautifully with mid-spring to early summer blooms like late tulips, columbines or foxgloves. Its soft blue pairs particularly well with silver or bronze foliage, or with orange blooms like Geum ‘Totally Tangerine’. Placed in borders, in cool rockeries, or even in partially shaded containers, it adds a light and poetic touch thanks to its airy foliage and luminous flowering.

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Polemonium: planting, growing and care
Family sheet
by Eva 10 min.
Polemonium: planting, growing and care
Read article

Flowering

Flower colour blue
Flowering time May to July
Inflorescence Corymb
Flower size 2 cm
Bee-friendly Attracts pollinators
Good for cut flowers Cut flower blooms

Foliage

Foliage persistence Deciduous
Foliage colour green

Plant habit

Height at maturity 45 cm
Spread at maturity 40 cm
Growth rate normal

Botanical data

Genus

Polemonium

Species

caeruleum

Cultivar

Blue Pearl

Family

Polemoniaceae

Other common names

Jacob's Ladder, Greek Valerian

Botanical synonyms

Polemonium caucasicum HORT.

Origin

Cultivar or hybrid

Product reference24572

Planting and care

Polemonium caeruleum ‘Blue Pearl’ is best sown between February and April, under heated cover (15–20 °C), in fine seed compost, kept moist but not waterlogged. Germination usually takes 20 to 30 days.
Transplant young plants into pots when they are strong enough, then plant them in the garden after the last frosts, in May.
Sowing in situ is possible, but more delicate, as emergence is slow and seedlings are sensitive to competition.
Plant in rich, moist, well-drained soil, in partial shade or gentle sun. Space the young plants about 30 cm apart to allow them to form attractive clumps. Water regularly for the first few weeks to encourage rooting, especially in hot weather. An organic mulch can help maintain soil moisture. Remove faded flowers to encourage a second flush and limit self-seeding.

Divide clumps every 3 to 4 years in spring to aerate the crown and rejuvenate it. ‘Blue Pearl’ is not very susceptible to pests but may be prone to powdery mildew if the atmosphere is too humid or confined: good air circulation will limit this risk.

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Sowing period

Sowing period February to April
Sowing method Sowing under cover
Germination time (days) 25 days

Intended location

Suitable for Meadow, Woodland edge
Type of use Border, Edge of border
Hardiness Hardy down to -23°C (USDA zone 6a) Show map
Ease of cultivation Beginner
Exposure Sun, Partial shade
Soil pH Acidic, Neutral
Soil moisture Moist soil, well-drained, humus-rich

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