Just Bloom Guide to Hydrangea Classifications
Hydrangeas are beloved flowering shrubs known for their spectacular blooms and adaptability to various garden conditions. Understanding their classifications helps gardeners select the right varieties and provide proper care. This Just Bloom florist guide explores both botanical taxonomy and practical gardening classifications.
Botanical Classification
Family and Genus
Family: Hydrangeaceae (formerly placed in Saxifragaceae)
Genus: Hydrangea
Origin: The genus name derives from Greek "hydro" (water) and "angeion" (vessel), referring to the cup-shaped seed capsules
Major Species Groups
Hydrangeas are classified into approximately 75 species worldwide, but several major species dominate cultivation:
1. Hydrangea macrophylla (Bigleaf Hydrangea)
Origin: Japan and Korea
Characteristics: Large, serrated leaves and globular or flat-topped flower clusters
Subspecies:
H. macrophylla subsp. macrophylla (garden hydrangeas)
H. macrophylla subsp. serrata (mountain hydrangeas)
2. Hydrangea paniculata (Panicle Hydrangea)
Origin: Eastern Asia
Characteristics: Cone-shaped flower panicles, tree-like growth habit
Notable varieties: 'Grandiflora', 'Limelight', 'Phantom'
3. Hydrangea arborescens (Smooth Hydrangea)
Origin: Eastern North America
Characteristics: Native species with white, dome-shaped flower clusters
Famous variety: 'Annabelle'
4. Hydrangea quercifolia (Oakleaf Hydrangea)
Origin: Southeastern United States
Characteristics: Oak-shaped leaves, cone-shaped white flowers, excellent fall color
Growth habit: Typically 4-6 feet tall and wide
5. Hydrangea anomala subsp. petiolaris (Climbing Hydrangea)
Origin: Asia
Characteristics: Vigorous climbing vine, white lacecap flowers
Growth: Can reach 30-50 feet when mature
6. Hydrangea aspera
Origin: China and Himalayas
Characteristics: Velvety leaves, lacecap flowers in various colors
Notable subspecies: H. aspera subsp. sargentiana
Horticultural Classifications
By Flower Type
Mophead (Hortensia)
Description: Large, rounded flower clusters composed entirely of sterile flowers
Appearance: Dense, ball-shaped blooms
Popular varieties: 'Nikko Blue', 'Endless Summer', 'Big Daddy'
Lacecap
Description: Flat-topped clusters with fertile flowers in center, surrounded by showy sterile flowers
Appearance: More natural, delicate appearance
Popular varieties: 'Blue Wave', 'Lanarth White', 'Tokyo Delight'
Panicle
Description: Cone or pyramid-shaped flower clusters
Species: Primarily H. paniculata
Characteristics: Usually starts white/cream, may age to pink
By Blooming Behavior
Old Wood Bloomers (Traditional)
Blooming habit: Form flower buds on previous year's growth
Pruning timing: Immediately after flowering (late summer)
Winter hardiness: More susceptible to bud damage from late frosts
Examples: Most H. macrophylla varieties, H. serrata
New Wood Bloomers (Remontant)
Blooming habit: Form flower buds on current year's growth
Pruning timing: Can be pruned in late winter/early spring
Advantages: More reliable flowering, especially in cold climates
Examples: H. arborescens, H. paniculata
Reblooming (Both Old and New Wood)
Blooming habit: Bloom on both previous and current year's growth
Advantages: Extended blooming season, more reliable flowering
Popular series: Endless Summer, Forever & Ever, Let's Dance
By Hardiness Zones
Cold Hardy (Zones 3-4)
Species: H. paniculata, some H. arborescens
Characteristics: Withstand temperatures to -30°F or lower
Examples: 'PeeGee', 'Grandiflora', 'Annabelle'
Moderate Hardy (Zones 5-6)
Species: H. quercifolia, hardy H. macrophylla varieties
Temperature range: -10°F to -20°F
Examples: 'Alice', 'Snow Queen', Endless Summer series
Tender (Zones 7-9)
Species: Most H. macrophylla, H. aspera
Temperature tolerance: Above 0°F to 10°F
Protection: May need winter protection in borderline zones
By Growth Habit
Shrub Forms
Height range: 2-12 feet depending on species
Growth pattern: Multi-stemmed, bushy growth
Examples: Most hydrangea species and varieties
Tree Forms (Standards)
Description: Trained to single trunk
Species: Primarily H. paniculata
Mature size: 10-25 feet tall
Dwarf Varieties
Height: Under 4 feet at maturity
Uses: Containers, small gardens, border fronts
Examples: 'Mini Penny', 'Little Lime', 'Bobo'
Climbing Forms
Species: H. anomala subsp. petiolaris, H. seemannii
Support needed: Walls, trees, trellises
Mature size: 30-80 feet
Color Classifications
pH-Dependent Color Change
Applies primarily to H. macrophylla and H. serrata:
Blue Hydrangeas
Soil requirement: Acidic soil (pH 5.0-5.5)
Aluminum availability: High (aluminum sulfate can be added)
Popular blue varieties: 'Nikko Blue', 'All Summer Beauty'
Pink Hydrangeas
Soil requirement: Alkaline soil (pH 6.0-7.0)
Aluminum availability: Low (lime can be added to raise pH)
Popular pink varieties: 'Forever Pink', 'Blushing Bride'
Purple Hydrangeas
Soil requirement: Neutral soil (pH 6.0-7.0)
Color result: Intermediate between blue and pink
Achievement: Often occurs naturally in mixed soil conditions
White Hydrangeas
Color stability: Generally unaffected by soil pH
Varieties: 'Annabelle', 'Incrediball', 'Blushing Bride' (starts white)
Fixed Color Varieties
Some species and varieties maintain consistent colors regardless of soil pH:
H. paniculata: Usually white aging to pink/red
H. arborescens: Predominantly white
H. quercifolia: White flowers
Regional Classifications
Japanese Hydrangeas (Ajisai)
Traditional varieties: Many H. macrophylla cultivars
Cultural significance: Associated with rainy season (tsuyu)
Breeding focus: Flower form, color intensity
European Garden Hydrangeas
Development: Heavily hybridized from Japanese introductions
Characteristics: Often larger flowers, different growth habits
Climate adaptation: Bred for European growing conditions
American Native Species
H. arborescens: Smooth hydrangea
H. quercifolia: Oakleaf hydrangea
Breeding programs: Focus on hardiness and native plant gardens
Modern Breeding Classifications
Proven Winners Selections
Endless Summer Series: Reblooming H. macrophylla
Incrediball Series: Improved H. arborescens
Little Lime Series: Dwarf H. paniculata
Bailey Nurseries (First Editions)
Let's Dance Series: Reblooming, compact varieties
Focus: Cold hardiness and reliability
Monrovia Selections
Various series: Emphasis on consistent performance
Garden-tested: Trialed across different climates
Care Considerations by Classification
Pruning Requirements
Group 1 (Old wood bloomers): Prune immediately after flowering
Group 2 (New wood bloomers): Prune in late winter/early spring
Group 3 (Both): Minimal pruning needed, deadhead for appearance
Fertilization Needs
Acid-loving varieties: Benefit from acidic fertilizers
General feeding: Balanced fertilizer in spring
Color enhancement: Specific amendments for desired colors
Winter Protection
Zone-appropriate: Choose varieties suited to your climate
Marginal hardiness: Provide mulch, burlap protection
Container growing: Move tender varieties to protection
Just Bloom Florist tips
Understanding hydrangea classifications helps gardeners make informed choices about variety selection, placement, and care. Whether you're drawn to the classic mophead blooms, prefer the delicate beauty of lacecaps, or want the reliability of newer reblooming varieties, there's a hydrangea classification that will thrive in your garden conditions.
The key is matching the right hydrangea type to your climate, soil conditions, and garden design goals. With proper selection and care, these magnificent shrubs will provide years of spectacular blooms and seasonal interest.
