Why are my leaves turning yellow?

This is often due to iron chlorosis caused by soil that is not acidic enough.

Do I need to prune them?

Only prune immediately after flowering to shape the plant and remove dead wood.

Plant guide

Rhododendron.

Rhododendron

Pronounced roh-duh-DEN-drun

Also known as Azalea, Rhododendron, Azaleas, Rhododendron, Rhododendrons, Rhododenron, Rosebay, azalea, rhododendrons and azaleas

Rhododendron indicum — Photo by Nicollas Michels (CC BY-SA) via iNaturalist

Rhododendrons are stunning woody shrubs known for their massive, showy flower clusters. They thrive in cool, moist environments with acidic soil. Most varieties prefer dappled shade to protect their foliage from harsh afternoon sun.

At a glance

Care level: Moderate
Plant type: Shrub
Light: Partial shade
Indoor light: Bright indirect
Water: Every 5 to 10 days
Mature size: 1 to 6 meters
Growth rate: Medium
Hardiness: USDA 4 to 9
Bloom time: Mid spring to early summer

Care

Keep the soil consistently moist but never waterlogged to prevent root rot. Mulch around the base to maintain root coolness and moisture. Watch for yellowing leaves which often signal poor drainage or incorrect soil pH.

Watering: Water deeply whenever the top few centimeters of soil feel dry.
Feeding: Apply an acid loving fertilizer once in early spring after flowering.
Pruning: Prune immediately after flowering to shape the shrub and remove dead wood.
Repotting: Repot only when the plant has clearly outgrown its container.
Soil: Well draining, acidic, organic rich soil
Soil pH: 4.5 to 6.0
Temperature: -25 to 30°C
Humidity: 60 to 90%
Drought tolerance: Low
Lifespan: Perennial, typically 20 to 50 years or more.
Fragrance: Light
Deer and rabbits: Low

Signs it needs repotting

Roots growing out of the drainage holes.
Water running straight through the pot without soaking in.
Stunted growth during the active season.

Safety

People: The plant contains grayanotoxins which are poisonous to humans and pets if consumed.
Pets: All parts of the plant are highly toxic to cats and dogs if ingested.
Children: Keep children away from the plant as ingestion of any part can lead to severe poisoning.
Contact allergens: The leaves and stems can cause mild skin irritation in sensitive individuals.
Airborne allergens: The pollen is generally not considered a major airborne allergen.
Edibility: All parts of the plant are highly toxic if ingested and can cause serious illness.

How to identify it

Large, leathery evergreen leaves
Showy, bell shaped flower clusters
Woody, multi stemmed growth habit
Leaves often have scaly undersides

Height: 0.6 to 4.5m
Spread: 0.6 to 4m
Leaves: dark green, evergreen
Flowers: pink, purple, white, red, yellow, 2 to 10cm
Fruit: brown, late summer

Problems to watch for

ChlorosisCommon
Lace BugCommon
PhytophthoraCommon
Leaf ScorchUncommon
Root RotUncommon
Vine WeevilUncommon

By symptom

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Growing it

Propagation: cuttings, seed, layering
When to plant: spring, autumn
Overwintering: Apply a thick layer of mulch around the base to protect roots from freezing temperatures. Ensure the soil remains moist but not waterlogged during dry winter spells.
In containers: They grow well in large containers, provided you use a high-quality, acidic potting mix and ensure excellent drainage.

Stem Cuttings

Take a 10 cm cutting from new growth in late summer.
Remove the lower leaves and dip the end in rooting hormone.
Plant in a mix of peat and perlite.
Cover with a plastic bag to maintain humidity.
Keep in bright, indirect light until rooted.

Group them with other acid-loving plants to make soil management easier.

Grows well with

Japanese Maple — They share similar requirements for acidic soil and partial shade.
Ferns — Ferns provide a beautiful textural contrast and thrive in the same woodland conditions.
Pieris — This companion shares the same cultural needs and blooms at a similar time.

Similar species

Azalea — Azaleas are technically a subgenus of Rhododendron with similar care needs.
Mountain Laurel — It is a related ericaceous shrub that thrives in identical woodland environments.

Science

Family: Ericaceae
Genus: Rhododendron
Order: Ericales
Class: Magnoliopsida
Native range: Widely distributed across the Northern Hemisphere, particularly in the Himalayas and North America.
Conservation: Some rare species are protected, but most common garden varieties are not of conservation concern.

They typically grow in cool, moist, acidic forest understories where they benefit from dappled shade.

Value to wildlife: nectar source, shelter for small birds
Pollinators: bees, butterflies, hummingbirds
Uses: ornamental shrub, woodland garden feature, privacy screen

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 1/9
Soil reaction: 3/9
Light: 4/9
Moisture: 6/9
Temperature: 5/9
Nutrients: 4/9

Taxonomy resolved against GBIF.

Questions people ask

Why are my leaves turning yellow?: This is often due to iron chlorosis caused by soil that is not acidic enough.
Do I need to prune them?: Only prune immediately after flowering to shape the plant and remove dead wood.

Where the name comes from

The name Rhododendron is derived from the Greek words rhodon, meaning rose, and dendron, meaning tree. It was named by Linnaeus to describe these woody plants with rose-like flowers.

Good to know

Rhododendrons are the national flower of Nepal.
The genus name comes from the Greek words for rose and tree.
Some species can grow into massive trees in their native habitats.
They prefer acidic soil to thrive.

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.