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Eupatorium coelestinum
Blue Mistflower
{Eupatorium coelestinum} (synonym {Conoclinium coelestinum}) is native to the eastern United States, from New Jersey south to Florida and west to Kansas and Texas; the species grows in moist meadows, stream margins, roadside ditches, and open woodlands on a range of soil types; the species name 'coelestinum' means 'sky-blue', referring to the soft blue flower color that is uncommon in the fall perennial palette
Overview
Eupatorium coelestinum (synonym Conoclinium coelestinum) is a native perennial growing 18-30 inches (45-75 cm) tall and wide. Flat-topped clusters of soft blue to violet-blue fluffy flowers resembling annual ageratum (Ageratum houstonianum) appear from August through October, giving among the rare true blue colors available in the fall garden when most blooming perennials are yellow, orange, and purple. The common name hardy ageratum references this ageratum-like flower appearance in a cold-hardy perennial format. The species spreads aggressively by rhizomes, forming expanding colonies that can overrun less vigorous neighbors in rich moist soil. In lean dry conditions, the spread is more manageable. This aggressive habit is the primary limitation — in confined garden settings, root barriers or periodic thinning are needed. Medium green triangular to heart-shaped coarsely toothed leaves cover the branching stems. Pinching stem tips by one-half in early June produces shorter bushier growth that is less prone to flopping. The late bloom is a major nectar source for monarch and other migrating butterflies in the fall. The species name 'coelestinum' means 'sky-blue'. Some taxonomists have moved this species to the genus Conoclinium spp.. Deer avoid the foliage.
Native Range
Eupatorium coelestinum is native to the eastern United States, from New Jersey south to Florida and west to Kansas and Texas. It grows in moist meadows, stream margins, roadside ditches, and open woodlands on a range of soil types.Suggested Uses
Used in naturalized plantings, meadow edges, and large-scale perennial borders where the aggressive spread is acceptable. The late-season blue gives fall butterfly nectar when few other blue flowers are available. Works in rain gardens and moist areas. Container culture in pots of 5 gallons (19 L) or more contains the rhizome spread. Not suited to small contained borders where the spread would overwhelm neighbors.How to Identify
Appearance
Size & Dimensions
Height1'6" - 2'6"
Width/Spread1'6" - 2'6"
Reaches mature size in approximately 2 years
Bloom Information
Flowering from August through October, approximately 6 weeks. Soft blue fluffy flower clusters cover the plant. Among the rare true blue fall flowers, complementing the yellow and orange tones that dominate the fall palette.Detailed Descriptions
Flower Description
Soft blue to violet-blue fluffy flat-topped flower clusters resembling annual ageratum (Ageratum houstonianum); among the rare true blue colors available in the fall garden when most blooming perennials are yellow, orange, and purpleFoliage Description
Medium green triangular to heart-shaped coarsely toothed leaves cover the branching stemsGrowing Conditions
Sun Requirements
Requires 5-10 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
Plant in full sun to partial shade with 5-10 hours of light. Average to moist soil. Water during dry spells. Pinch all stem tips by one-half in early June for shorter bushier more compact growth. The aggressive rhizome spread requires management — contain with root barriers, regular thinning, or placement in areas where spreading is acceptable. Cut all stems to ground level in late fall or early spring.Pruning
Pinch stem tips by one-half in early June for compact growth. Cut all stems to ground level in late fall or early spring. Thin rhizome spread by removing outlying shoots as needed.Pruning Schedule
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summerfallearly spring
Maintenance Level
moderateContainer Growing
✓ Suitable for container growing
Minimum container size: 5 gallons