Formosa azalea

Sun

Partial shade, preferably morning sun and afternoon shade. Tolerates more sun where summers are mild and the soil stays moist.

Water

Keep the shallow root zone evenly moist, especially during establishment and hot, dry weather; avoid waterlogged soil.

Soil

Acidic soil, ideally pH 4.5-6.0, rich in organic matter and freely drained. Unsuitable for chalky or persistently wet ground.

Height

6-8 ft (1.8-2.4 m)

Spread

6-10 ft (1.8-3 m)

Flowers

Early to mid-spring; large, funnel-shaped purple-magenta flowers with darker spotting on the upper petals.

Foliage

Evergreen. Dark green, oval to elliptic leaves on a densely branched shrub; some older leaves may yellow and drop during seasonal turnover or cold weather.

Growth

Moderate

Care needed

Medium

• Pollinators
• Heat tolerant
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Needs looking after

Pick your zone, country, light and whether you have pets.

1. Planting day

   1.6 ft (0.5 m)

2. After 1 year

   2.7 ft (0.82 m)

3. After 2 years

   4 ft (1.1 m)

4. After 3 years

   5 ft (1.5 m)

5. After 5 years

   7 ft (2.1 m)

   full size

About 5 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Growth rate

Moderate

• Plant with the top of the root ball level with, or slightly above, the surrounding soil; do not bury the crown.
• Water deeply during dry spells, checking beneath the mulch rather than relying on surface appearance.
• Apply 2-3 in (5-8 cm) of pine bark or leaf mould, keeping it clear of the stems.
• If growth is weak, feed lightly with an azalea fertiliser after flowering; avoid heavy feeding and late-season nitrogen.
• Avoid digging around the shallow roots; remove weeds by hand.

Pruning. Prune immediately after flowering, shortening overlong shoots and removing dead or crossing branches. Avoid late-summer, autumn or winter trimming, which removes the following spring's flower buds.

Spring

Check soil moisture as buds open, and water during dry weather.

Late spring

After flowering, prune selectively and feed lightly if needed.

Summer

Maintain even moisture and inspect leaf undersides for lace bugs.

Late summer

Take semi-ripe cuttings; stop pruning so next spring's flower buds remain intact.

Autumn

Plant in mild regions and renew mulch without covering the crown.

Winter

Water during prolonged dry spells when the ground is unfrozen, and protect container roots from hard freezes.

• Plant as an informal flowering hedge along a shaded boundary, allowing room for its mature width.
• Group beneath high-canopied trees with camellias and ferns for layered woodland planting.
• Use behind lower shrubs and perennials, where its evergreen foliage provides a year-round backdrop.
• Place beside a broad entrance or terrace in acidic soil, leaving space so repeated shearing is unnecessary.

Garden styles it suits: Southern, Traditional, Woodland, Japanese, Romantic rose garden and Grand estate.

Plant it with: Camellias, Japanese pieris, Japanese maples, Hydrangeas, Hostas and Autumn ferns.

Wildlife: Flowers attract visiting bees and other pollinating insects. Dense branches provide shelter for small birds, but this cultivated shrub is not a substitute for locally native habitat plants.

• Azalea lace bugs cause pale stippling above and dark specks beneath leaves. Reduce drought stress and spray leaf undersides with insecticidal soap labelled for azaleas, repeating as directed.
• Phytophthora root rot causes wilting and dieback in wet soil. Improve drainage before planting; remove badly affected plants and do not replace them in the same poorly drained spot.
• Yellow leaves with green veins often indicate iron deficiency from alkaline soil or water. Test the soil, address the pH problem and use an appropriate chelated iron product for temporary relief.
• Petal blight makes flowers develop watery spots and collapse. Remove affected flowers and fallen petals, avoid overhead watering during bloom and improve air circulation.

Toxic to people, cats, dogs and horses. All parts, including leaves, flowers and nectar, contain grayanotoxins; ingestion can cause vomiting, weakness, low blood pressure and dangerous heart rhythm changes. Suspected ingestion needs prompt medical or veterinary advice.

• George L. Taber azalea (Rhododendron 'George L. Taber')

  Has pale pink to nearly white flowers with a conspicuous darker pink-purple blotch, rather than the strong purple-magenta flowers of 'Formosa'.

• Mrs. G. G. Gerbing azalea (Rhododendron 'Mrs. G. G. Gerbing')

  Has large white flowers; its evergreen foliage and broad growth habit are similar, so identification is easier during bloom.

Rhododendron comes from the Greek words for rose and tree, referring to the showy flowers of these woody plants.

Propagation. Take semi-ripe cuttings in summer and root in an acidic, freely drained medium under high humidity. Layering low branches also works; seed does not reliably produce plants identical to 'Formosa'.

Accepted botanical name

Rhododendron

Sources: GBIF (CC BY 4.0). The care and design notes are LandscapeGPT's own.