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Rhododendron 'Herbert'
Herbert Rhododendron
Hybrid of garden origin; bred by Joseph Gable in Stewartstown, Pennsylvania; the Gable hybrids were selected specifically for cold hardiness in Pennsylvania winters and carry cold tolerance to USDA zone 5 — a zone harder than the zone 6 limit of most other evergreen azalea groups
Overview
Rhododendron 'Herbert' is an evergreen azalea reaching 3-4 feet (0.9-1.2 m) tall with a spread of 3-4 feet (0.9-1.2 m) and a compact, dense, upright-to-rounded habit. A Gable hybrid developed by Joseph Gable in Stewartstown, Pennsylvania, the cultivar carries semi-double to double (hose-in-hose) flowers 2 inches (5 cm) wide in reddish-purple to purple-violet, densely covering the plant in May; bloom duration is 3-4 weeks. Small elliptic leaves 1-2 inches (2.5-5 cm) long are glossy dark green and turn reddish-bronze to purplish in winter, giving a second seasonal color display after the spring bloom ends. Growth rate is moderate. Hardy to USDA zone 5 — a zone harder than the zone 6 limit of most other evergreen azalea groups. Toxic to pets and humans if ingested. The Gable hybrids were bred specifically for cold hardiness in Pennsylvania winters, and 'Herbert' carries the group's zone 5 tolerance together with a double-flowered purple color combination that is not common in the hardy azalea market.
Native Range
Rhododendron 'Herbert' is a hybrid of garden origin, bred by Joseph Gable at his Stewartstown, Pennsylvania nursery as part of the Gable series of cold-hardy evergreen azaleas.Suggested Uses
Used in mass plantings, mixed borders, and foundation plantings in zones 5-9 at 3-4 foot (0.9-1.2 m) spacing. USDA zone 5 cold hardiness extends the planting range north of most evergreen azaleas and suits colder-zone gardens that cannot support the zone 6 groups. Winter foliage color — reddish-bronze to purplish from late autumn through early spring — adds a second seasonal interest window beyond the May bloom. Containers of 3 gallons (11 L) minimum suit the compact habit. Toxic to pets and humans if ingested, so not suited to sites where pets or small children may browse plant material. Also not suited to alkaline soils, full sun in hot climates, or dry conditions.How to Identify
Appearance
Size & Dimensions
Height3' - 4'
Width/Spread3' - 4'
Reaches mature size in approximately 6 years
Bloom Information
Semi-double to double (hose-in-hose) reddish-purple to purple-violet flowers 2 inches (5 cm) wide densely covering the plant in May. Bloom duration is 3-4 weeks.Detailed Descriptions
Flower Description
Reddish-purple to purple-violet semi-double to double (hose-in-hose) flowers 2 inches (5 cm) wide densely covering the plant; MayFoliage Description
Glossy dark green leathery leaves; small elliptic 1-2 inches (2.5-5 cm) long; turning reddish-bronze to purplish in winterGrowing Conditions
Sun Requirements
Requires 3-6 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
Grows in partial shade in moist, well-drained, acidic soil at pH 4.5-6.0. Hardy to USDA zone 5. Cold tolerance exceeds the zone 6 limit of most other evergreen azaleas, so the cultivar suits Pennsylvania, Ohio Valley, and upper Midwestern gardens where evergreen azaleas are otherwise difficult. Winter foliage turns reddish-bronze to purplish, a seasonal color shift that reverses as new spring growth emerges. Mulch the root zone 2-3 inches (5-8 cm) deep with pine bark, pine needles, or oak leaves to hold moisture and protect the shallow root system. Toxic to pets and humans if ingested.Pruning
Prune lightly after flowering to shape if wanted. Avoid pruning after July — next year's flower buds form in summer. The compact form develops naturally and needs no structural pruning.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late spring
Maintenance Level
lowContainer Growing
✓ Suitable for container growing
Minimum container size: 3 gallons