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Growing Zones
USDA Hardiness Zones
6 - 8These zones indicate the coldest temperatures this plant can typically survive.
What's my zone? →Frost Tolerancehardy
Key Features
Maintenancelow
Overview
Glandora diffusa (formerly Lithodora diffusa) is lithodora (spreading gromwell), a prostrate evergreen sub-shrub growing 6–12 inches (15–30 cm) tall and spreading 12–24 inches (30–60 cm). Vivid gentian-blue funnel-shaped flowers 0.5–0.75 inch (12–18 mm) from late spring through midsummer (May–July). The gentian-blue flower color is among the purest blues of any groundcover plant — the color does not shift toward purple or violet. Dark green narrow hairy evergreen leaves 0.5–1 inch (12–25 mm). The cultivar 'Heavenly Blue' (syn. 'Grace Ward') is the most commonly grown selection. In the borage family (Boraginaceae). Acidic soil required (pH 5.0–6.5) — intolerant of alkaline soil (iron chlorosis and decline at pH above 6.5). Sharp drainage is non-negotiable — root rot in heavy wet soil or waterlogged winter conditions is the primary cause of failure. The stems become woody and bare at the base over time — shearing after flowering promotes denser growth from the cut points, but do not cut into old bare wood (it will not regenerate). Native to southwestern Europe (Spain, Portugal, southwestern France), growing on rocky acidic slopes and in open scrub. Non-toxic. Deer-resistant. Drought-tolerant once established. Full sun (6+ hours). Zones 6–8. Growth rate is moderate.
Native Range
Native to southwestern Europe (Spain, Portugal, southwestern France), growing on rocky acidic slopes and in open scrub.Suggested Uses
Grown in rock gardens, over retaining walls, and in raised beds in zones 6–8. Acidic soil required. Sharp drainage. The pure gentian-blue flower color is the primary feature. Cascading over edges. Non-toxic. Deer-resistant.How to Identify
Appearance
Size & Dimensions
Height6" - 1'
Width/Spread1' - 2'
Reaches mature size in approximately 2 years
Bloom Information
Late spring to midsummer (May–July), lasting 6–8 weeks. Vivid gentian-blue funnel-shaped flowers. Sporadic rebloom after shearing. 'Heavenly Blue' is the most common cultivar.Detailed Descriptions
Flower Description
Vivid gentian-blue, funnel-shaped, 0.5-0.75 inch (12-18 mm)Foliage Description
Dark green, narrow, hairy, 0.5-1 inch (12-25 mm)Growing Conditions
Sun Requirements
Requires 6-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Full sun (6+ hours). Acidic soil pH 5.0–6.5 — intolerant of alkaline soil. Sharp drainage non-negotiable (root rot in wet soil). Shear after flowering — do not cut into old bare wood. Drought-tolerant once established. Non-toxic. Deer-resistant. Zones 6–8.Pruning
Shear lightly after the main flowering flush (July–August) to encourage denser growth and sporadic rebloom. Do not cut into old bare woody stems — they will not regenerate. The prostrate form cascades over walls and raised bed edges.Pruning Schedule
J
F
M
A
M
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J
A
S
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D
summer
Maintenance Level
lowContainer Growing
✓ Suitable for container growing
Minimum container size: 3 gallons