Rhododendron Irene Koster

Irene Koster Rhododendron

Irene Koster (Rhododendron ‘Irene Koster’) is a deciduous azalea with white and pink flowers. Its display arrives in the later part of the rhododendron flowering season, with the exact timing influenced by local weather. Individual flowers measure about 2½ inches across. The flower tubes widen into flared faces that display the color clearly. Wavy petal edges give the clusters additional texture. The flowers are fragrant. Contrasting yellow markings add detail within the flower faces.

The shrub sheds its leaves for winter, making its seasonal foliage and flower display especially noticeable. Allow space for the branches to develop without crowding nearby plants or paths.

Give it acidic, humus-rich soil that stays moist and drains freely. A sheltered position with filtered light or morning sun is a useful starting point; protect the roots from prolonged drying and keep mulch clear of the stems.

Size guide
• Height: About 6 ft at 10 years; growth continues afterward
• Width: Allow for the cultivar’s natural branch spread; a verified numerical spread is not available in this reference.

Hardiness
• Approximate cold tolerance: -15°F
• USDA cold-limit equivalent: Zone 5b
This equivalence is calculated from the published temperature rating. Local conditions and summer climate also affect performance.

Best Uses
• Border
• Woodland Gardens
• Accent Plant

Plant type

Deciduous Shrub, Flowering Deciduous Shrub

Height

6 ft+

Width

6-8 '

Hardiness zones

5b–9

Sunlight

Part shade

Growth rate

Slow

Bloom time

Spring to summer

Flower color

Pink, White

Leaf color

Green

Fall color

Green

Attracts

Butterflies

Soil

Acidic, Humus rich, Moist well-drained

Landscape use

Accent Plant, Border, Woodland Gardens

Bark

Smooth

Fruit

No

Fragrant

Yes

Deer resistant

No

Salt tolerant

No

Drought tolerant

No

10-year height

6 ft