Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Lobelia siphilitica
Blue Cardinal Flower, Great Blue Lobelia
I planted 3 young plants and they all held up well in moist soil conditions, sensitive to drought, beautiful flowering.
pascale, 01/09/2025
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Description
The Lobelia siphilitaca or Syphilitic Lobelia is a charming perennial that thrives in moist to wet soil and deserves to be used more often in gardens. It has upright stems with large leaves at their base and large floral spikes, from early summer to early autumn, composed of blue flowers tinged with mauve. It prefers sunny, non-scorching exposures, but also not too dense shade. A perfect plant for flowering in your woodland areas or pond edges.
The Syphilitic Lobelia is a tall, erect perennial native to North America. It has a fast growth rate and can reach 60 to 90 cm (24 to 35in) in height with a spread of 30 cm (12in) per stem. Its leaves are dark green and lanceolate, alternating along the stem. They start off large at the base of the stem and become progressively smaller towards the floral spike, similar to foxglove leaves. From August to October, floral spikes at the top of the stems reveal flowers that progressively open along the spikes. Its beautiful blue flowers tinged with mauve have a trumpet shape, similar to Snapdragons (Antirrhinum majus), ending with two cut, outward-curved lips. This perennial tends to have a short lifespan, but self-seeds under favorable conditions without becoming invasive. Its above-ground, deciduous vegetation dries up in autumn and regrows in spring.
The Syphilitic Lobelia is highly frost hardy (-20° C). Allow for a relatively large space for the plant to develop and charm you with its vigor. It thrives in heavy, ordinary, moist to wet soils and can tolerate short periods of root submersion. It enjoys sunny exposures with moist soil, but also shaded exposures in a consistently moist summer soil. It is ideal for water gardens, pond edge plantings, and woodland areas. Its striking habit is complemented by Phlox, Grasses, Goat's Beards, and Astilbes.
Lobelia siphilitica in pictures
Flowering
Foliage
Plant habit
Botanical data
Lobelia
siphilitica
Campanulaceae
Blue Cardinal Flower, Great Blue Lobelia
North America
Planting and care
Pretty hardy and robust young plant that grows in moist to wet soil, in non-burning sun or partial shade. It prefers a soil rich in humus, well-drained, alkaline or neutral.
Planting period
Intended location
Care
Planting & care advice
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Hardiness is the lowest winter temperature a plant can endure without suffering serious damage or even dying. However, hardiness is affected by location (a sheltered area, such as a patio), protection (winter cover) and soil type (hardiness is improved by well-drained soil).
In temperate climates, pruning of spring-flowering shrubs (forsythia, spireas, etc.) should be done just after flowering.
Pruning of summer-flowering shrubs (Indian Lilac, Perovskia, etc.) can be done in winter or spring.
In cold regions as well as with frost-sensitive plants, avoid pruning too early when severe frosts may still occur.
The harvesting period indicated on our website applies to countries and regions in USDA zone 8 (France, England, Ireland, the Netherlands).
In colder areas (Scandinavia, Poland, Austria...) fruit and vegetable harvests are likely to be delayed by 3-4 weeks.
In warmer areas (Italy, Spain, Greece, etc.), harvesting will probably take place earlier, depending on weather conditions.
The sowing periods indicated on our website apply to countries and regions within USDA Zone 8 (France, UK, Ireland, Netherlands).
In colder areas (Scandinavia, Poland, Austria...), delay any outdoor sowing by 3-4 weeks, or sow under glass.
In warmer climes (Italy, Spain, Greece, etc.), bring outdoor sowing forward by a few weeks.
The planting period indicated on our website applies to regions in USDA Zone 9a (East Coast and Midlands: Dublin, Wexford, Waterford, Kilkenny, Portlaoise). It will vary depending on where you live:
- On the west coast and in the north-west (Galway, Limerick, Sligo, Donegal, Westport), delay planting by 1 to 2 weeks in spring and bring it forward by 1 to 2 weeks in autumn compared to the dates given, preferably choosing periods without strong winds.
- In the inland hills and plateaus (Wicklow Mountains, Macgillycuddy’s Reeks, Connemara, Killarney), it is best to plant in spring (April–May) or autumn (September–October), avoiding periods of waterlogged soil in winter and strong winds, which pose the main risk to newly planted trees in these areas.
The flowering period indicated on our website applies to regions in USDA Zone 9a, such as the East Coast and Midlands, including Dublin, Wexford, Waterford, Kilkenny and Portlaoise.
This will vary depending on where you live:
- On the west coast and in the northwest (Galway, Limerick, Sligo, Donegal and Westport), it will be delayed by one to two weeks compared to the given dates, due to stronger Atlantic winds and less spring sunshine.
- In the inland hills and plateaus (the Wicklow Mountains, the Macgillycuddy's Reeks, Connemara and Killarney), flowering will be delayed by two to three weeks. Flowering mainly occurs between May and July, with the limiting factors being less frost and more of the excessive humidity, strong winds and lack of sunshine that are characteristic of these areas.
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