How to Grow Underwood Azalea

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Underwood Azalea

Rhododendron × 'Underwood'

shrub

Underwood azalea is a hybrid evergreen shrub prized for its vibrant deep pink to red flowers that bloom in mid to late spring. This compact, dense cultivar is particularly valued for its cold hardiness and reliable flowering, making it an excellent choice for northern gardens. It produces glossy foliage that provides year-round interest and reaches a moderate size suitable for landscapes and foundation plantings.

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Example Underwood Azalea timeline · Pittsburgh, PA (Zone 6b)

Plant Underwood Azalea
Around Apr 17

Near Pittsburgh's average last spring frost.
Tend & protect
Late spring–summer

Watering, feeding, and pest-watch reminders.
Harvest Underwood Azalea
Late summer into fall

Before the first fall frost (≈ Nov 8)

Sample dates for Pittsburgh, PA. Sign up to get exact Underwood Azalea dates for your own zip code.

Growing Conditions

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Sun: Partial shade, 3-6 hours of morning sun daily; afternoon shade is beneficial in warmer zones

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Water: Consistently moist but well-draining soil; water deeply during dry spells, especially during the growing season and first year after planting. Azaleas are shallow-rooted and prefer evenly moist conditions. Reduce watering in winter.

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Spacing: 48-60 inches

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Days to maturity: Not applicable (woody shrub); reaches mature size in 7-10 years

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Planting depth: Plant at or slightly shallower than root ball depth; do not bury the stem

Soil

Type: Well-draining acidic soil, preferably with high organic matter content

pH: 4.5-5.5

Amendments:

Peat moss Pine bark Compost Sulfur (if soil pH is too high)

Growing Zones

Find your zone →

Thrives in zones 5-8, with best performance in zones 5b-7b

5a 5b 6a 6b 7a 7b 8a

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Growth Stages

Establishment (Year 1)

12 months

Young plant develops root system and establishes in the landscape with minimal flowering

Water regularly and deeply, maintain consistent moisture. Apply 2-3 inches of organic mulch around base (keeping away from stem). Avoid heavy pruning; remove only dead or crossing branches.

Vegetative Growth (Spring-Early Summer)

4-6 weeks

Plant puts out new shoots and leaves following spring bloom; foliage is bright green and expanding

Continue consistent watering. Light fertilization with azalea-specific fertilizer (low nitrogen) after flowering. Prune lightly after bloom if needed to shape.

Flower Bud Formation (Summer-Early Fall)

8-10 weeks

Buds for next season develop along branch tips; foliage matures to deep green

Maintain moisture during hot, dry periods. Avoid excessive nitrogen fertilizer which can inhibit flowering. Do not prune after early summer as you'll remove developing flower buds.

Dormancy (Fall-Winter)

8-12 weeks

Foliage may take on bronze or burgundy tones (depending on winter severity); plant enters rest period

Reduce watering but don't let soil dry out completely. No fertilizer. Mulch well to protect shallow roots in harsh winters. Underwood is cold-hardy but benefits from wind protection in zone 5.

Flowering (Mid-Late Spring)

2-4 weeks

Dense clusters of deep pink to red flowers bloom along branches, creating a showy display

Enjoy the blooms; deadheading spent flowers can encourage more blooms but is not essential. Avoid spraying with pesticides during bloom to protect pollinators.

Companion Planting

Plan your garden →

Plant with:

Daffodils Candytuft Bleeding heart Japanese ferns Hostas Astilbe Hellebores Boxwood

Avoid planting near:

Walnuts (juglone toxicity) Highly competitive evergreens in too-close proximity

Common Pests

Spray undersides of leaves with horticultural oil or insecticidal soap in early spring and summer; encourage natural predators
Increase humidity, spray with water to dislodge; use miticide if severe; avoid drought stress
Yellow sticky traps, insecticidal soap, or neem oil spray
Hand-pick on small plants; use Bacillus thuringiensis (Bt) for larger infestations
and (fungal: Exobasidium, Phytophthora)
Ensure excellent drainage, avoid overwatering, remove infected plant material; apply fungicide if needed

Uses

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Ornamental Landscaping

Household

Underwood azaleas are premier spring-blooming shrubs for foundation plantings, mixed borders, woodland gardens, and shaded landscape beds. Their compact form, reliable flowering, and cold hardiness make them invaluable for creating color and structure in temperate gardens. [source]

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Cut Flowers & Arrangements

Household

The vibrant flower clusters make excellent additions to spring floral arrangements and can brighten indoor spaces. Cut early in the morning and condition in water immediately for best vase life (typically 1-2 weeks). [source]

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Pollinator Support

Wildlife

Azalea flowers attract bees, butterflies, and other pollinators, supporting local ecosystems during the spring bloom period. The plant provides early-season nectar when other food sources are limited. [source]

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Pressed Flowers & Crafts

Craft

The delicate flowers can be pressed for botanical crafts, bookmarks, and decorative projects. The vibrant color is retained reasonably well through the pressing process. [source]

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Traditional Uses

Medicinal

While not commonly used medicinally today, rhododendrons and azaleas have a history of use in traditional medicine in parts of Asia for treating inflammation and cough, though modern use is limited. [source]

This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.

Harvest Tips

Azaleas are not harvested but rather enjoyed for ornamental flowers and foliage. Flowers can be cut for indoor arrangements by snipping stems early in the morning. Deadheading (removing spent flower clusters) after bloom encourages bushier growth and potentially more blooms next season, though it is not required.

Fun Facts

🌱 Underwood azalea was developed as a cold-hardy hybrid specifically to thrive in northern climates where many other azalea varieties struggle, making it a breakthrough for gardeners in zones 5-6.
🌱 Azaleas and rhododendrons are both members of the Ericaceae family and have a symbiotic relationship with mycorrhizal fungi in the soil, which helps them absorb nutrients from acidic soils where most plants would struggle.
🌱 The deep pink flowers of Underwood azalea often intensify in color when exposed to cooler spring temperatures, creating a more vivid display in regions with variable spring weather.

Gardening Terms

New to gardening? Learn about terms used in this guide:

Cultivar Deadhead Hybrid Mulch Partial Shade

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