Flame azalea

Sun

Partial shade or filtered sunlight; morning sun with afternoon shade is ideal. More sun is suitable where summers are cool and the soil stays moist.

Water

Keep evenly moist but never waterlogged; water during dry spells, especially while establishing and during flower-bud formation in summer.

Soil

Acidic, humus-rich, well-drained soil, ideally pH 4.5-6.0. Avoid chalky soil and heavy, poorly drained clay.

Height

6-12 ft (1.8-3.7 m)

Spread

6-10 ft (1.8-3 m)

Flowers

Late spring to early summer; clusters of yellow, orange, scarlet or orange-red flowers, usually opening as the leaves emerge.

Foliage

Soft green, oval leaves with fine hairs, turning yellow, orange or reddish in autumn; autumn colour varies.

Growth

Slow to moderate

Care needed

Medium

• Pollinators
• Low allergen

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

Difficulty

Moderate

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

   2.8 ft (0.85 m)

3. After 2 years

   4 ft (1.2 m)

4. After 3 years

   5 ft (1.5 m)

5. After 5 years

   7 ft (2.2 m)

About 7 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

Native to

the US

Growth rate

Slow

• Plant with the top of the root ball level with, or slightly above, the surrounding soil; do not bury the root collar.
• Water deeply during dry weather, keeping the shallow root zone moist without leaving it saturated.
• Maintain a 2-3 in (5-8 cm) mulch of leaf mould, pine bark or composted bark, keeping it clear of the stems.
• If growth is weak, apply a light feed formulated for rhododendrons in spring; avoid heavy or late-season feeding.
• Keep cultivation and digging away from the shallow roots; remove nearby weeds by hand.

Pruning. Prune only as needed immediately after flowering, shortening wayward shoots and removing damaged or crossing branches. Avoid routine shearing or late-season pruning, which removes the following year's flower buds.

Early spring

Check winter damage and soil moisture; apply a light rhododendron feed only if needed.

Spring

Plant in workable soil, water thoroughly and mulch without covering the root collar.

Late spring to early summer

Enjoy the flowers, then carry out any necessary shaping as soon as flowering finishes.

Summer

Water during dry spells and inspect leaf undersides for lace bugs.

Autumn

Refresh the organic mulch and water well before winter if the soil is dry.

Winter

Check drainage and protect young plants from browsing rabbits or deer where needed.

• Plant in loose groups along a woodland edge for a bright late-spring display against green foliage.
• Combine with evergreen rhododendrons to give a mixed shrub border contrasting foliage and seasonal colour.
• Use beside a shaded path with ferns and foamflowers beneath it, allowing room for its open branching habit.
• Include in an eastern North American native garden with mountain laurel and other acid-soil woodland plants.

Garden styles it suits: Woodland, Wildlife garden, Pollinator garden, English country, Mountain lodge and Traditional.

Plant it with: Mountain laurel, Evergreen rhododendrons, Japanese pieris, Christmas fern, Foamflower and Solomon's seal.

Wildlife: Flowers attract bumblebees and butterflies, including swallowtails. Its native range supports specialist insects associated with azaleas; deer may browse the shoots and buds.

• Azalea lace bugs cause pale stippling and dark specks beneath leaves. Reduce drought stress, avoid hot exposed sites and treat leaf undersides with insecticidal soap if needed, following the label.
• Phytophthora root rot causes wilting and root decline in wet soil. Improve drainage before planting, keep the root collar exposed and remove badly affected plants.
• Powdery mildew can mark foliage, especially in crowded conditions. Improve air circulation, maintain steady soil moisture and remove fallen affected leaves.
• Yellow leaves with green veins often indicate iron deficiency caused by alkaline soil. Test the soil; use an acidic raised bed or suitable container rather than repeatedly treating unsuitable ground.

All parts, including leaves, flowers and nectar, contain grayanotoxins and are poisonous to people, cats, dogs and horses if eaten. Poisoning can cause vomiting, weakness, low blood pressure and dangerous heart disturbances; substantial ingestion can be fatal. Seek urgent medical or veterinary advice after suspected ingestion.

• Cumberland azalea (Rhododendron cumberlandense)

  Also has orange to red flowers, but generally blooms later, after the leaves have fully expanded, and is usually a smaller shrub.

• Florida flame azalea (Rhododendron austrinum)

  Usually has fragrant yellow to orange flowers with long, slender tubes, opening before or with the first leaves; flame azalea flowers are generally not fragrant and have broader, showier lobes.

• Sweet azalea (Rhododendron arborescens)

  Has strongly fragrant white to pinkish flowers with conspicuous red stamens, rather than the yellow, orange or red flowers of flame azalea.

The epithet calendulaceum means resembling Calendula, referring to its marigold-like flower colours, while flame azalea describes the fiery shades of its blooms.

Propagation. Raise from seed surface-sown on a moist, acidic medium with light and gentle warmth; seedlings vary in flower colour and take several years to bloom. Layering low branches is a practical way to preserve a particular plant. Cuttings are possible but can be difficult to root.

Accepted botanical name

Rhododendron calendulaceum

In the US and Canada

Native in the lower 48 states.

Native range

Alabama, Georgia, Kentucky, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia and Maryland.

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