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Blueblossom
Habit (mature) · Miguel Vieira / Wikimedia Commons · CC BY 2.0
Limited coverage
Blueblossom
Ceanothus thyrsiflorus
The hardiest and largest of the California lilacs — a fast-growing broadleaf-evergreen shrub of the Pacific coast that smothers itself in dense thyrse clusters of pale-to-deep blue flowers in spring. Glossy three-veined, finely toothed dark-green leaves and a billowing shrub habit make it a signature blue mass on West Coast slopes. Drought tolerant once established, it asks for little summer water and resents overwatering; deer and elk browse the foliage and the bloom is a documented draw for native bees.
Native: CA, OR
Review: Source-backed
Climate fit: narrow (26/100)
Focal point
Structure
Pollinator
Light
Full sun / Part shade
Water
Low water
Mature size
72-240" tall · 84" apart
Hardy in zones
8a-10b
cold to mild winters
Summer heat range
Warm-Hot
warm to hot summers Interim Plotwright tier until the plant AHS range is authored.
Native in Illinois
No
A documented larval host for the Spring azure — caterpillars feed on its foliage before becoming the next generation.
Wildlife relationships
Cold hardiness
Now
Zone 6b
USDA
Chicago, IL · 1991-2020 average annual coldest day
Source: USDA Plant Hardiness Zone Map 2023 (1991-2020 climatology) via ArcGIS FeatureServer
Won't grow here
2050
Zone 7b
Plotwright
Your zone + climate-model shift · SSP3-7.0 (regional rivalry)
Won't grow here
In plain terms: cold winters — coldest nights typically around -3°F.
Out of range today and still out of range in 2050.
Heat tolerance
Loading current AHS heat-zone and plant heat-fit data at your coordinates…
Sources & citations
Cite this page
For lesson plans, articles, or research that uses this page. To cite a single upstream fact instead, use its specific source listed below.
Plotwright. (2026, May 17). Blueblossom (Ceanothus thyrsiflorus). Retrieved 2026, June 5, from https://plotwright.garden/plants/blueblossom-ceanothus
Sources for every fact
Every fact on this page traces to a source. 18 fields cited18 source-backed.
Missouri Botanical Garden PlantFinder
Botanical research database
Backs 17 fields
Identity
Summary
Plant type
Light
Moisture
Hardiness
Heat zone
Size
Spacing
Habit
Design roles
Seasonal interest
Growth stages
Lifecycle
Regional guidance
Success tips
Designer notes
Wikimedia Commons
Photo · CC BY 2.0
Backs 1 field
Image
Community photos
The photos above are our reviewed reference set, curated for accuracy.
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