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Plant care

Azalea 'Gibraltar' (Gibraltar Azalea) care

Rhododendron 'Gibraltar'

Also called Gibraltar Azalea, Knap Hill Azalea, Deciduous Azalea 'Gibraltar'.

RHS H6USDA 5-8Toxic to petsIndoor 1.5-2 m tall and wide

Watering rhythm

Bright indirect light (just back from a sunny window)

Deeply once or twice a week in dry weather; keep consistently moist year-round

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Light

Bright indirect light (just back from a sunny window)

Soil

Ericaceous (acid), humus-rich, moisture-retentive but free-draining

Humidity

50-80%

Temp

-15-20°C

Pet safety

Toxic to pets

Mature size

1.5-2 m tall and wide

Care at a glance

Light

Bright but filtered. Azalea 'Gibraltar' burns within days in unfiltered south-facing summer sun, and stops growing within months in deep shade. Thrives in dappled shade or partial shade with some morning sun. Avoid intense afternoon sun, which causes petal scorch and bleaching. Under a light tree canopy is ideal. If you only have a south window, set the plant back 1.5 m or hang a sheer curtain — both knock the intensity down into the right range.

Watering

Watering azalea 'gibraltar': deeply once or twice a week in dry weather; keep consistently moist year-round. The number that matters isn't the day of the week — it's how dry the top 2-3 cm of the pot feels. A finger in the soil tells you more than a watering app. After every watering, tip the saucer. Rhododendrons and azaleas are sensitive to drought and waterlogging alike. Use soft water where possible — hard, alkaline tap water can raise soil pH over time. Never let the root ball fully dry out.

Soil and pot

Azalea 'Gibraltar' grows best in ericaceous (acid), humus-rich, moisture-retentive but free-draining. Must have acid soil pH of 4.5-6.0 — alkaline soil causes lime-induced chlorosis. Use ericaceous compost and plant shallowly (fibrous roots sit near the surface). Avoid lime or general fertilisers. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Azalea 'Gibraltar' sits happiest at around 50-80% humidity and -15-20°C (5-68°F). Prefers moderate to high humidity as found in woodland environments. In dry climates, mulching with bark chips conserves moisture and maintains a cooler, more humid root microclimate. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed azalea 'gibraltar' sparingly. Apply a specialist ericaceous or rhododendron fertiliser in mid-spring after flowering. Avoid high-nitrogen feeds that reduce flowering. Do not feed after midsummer as late growth is vulnerable to frost. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on azalea 'gibraltar' in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Lime-induced chlorosis — Yellow leaves with green veins indicate alkaline soil or hard water. Apply sequestered iron or re-pot into ericaceous compost; water with rainwater.
  • Rhododendron powdery mildew — White or pale patches on leaves. Improve airflow, reduce overhead watering, and apply a suitable fungicide.
  • Vine weevil — Adult beetles notch leaf edges; larvae destroy roots. Apply nematode biological controls in late summer and autumn.
  • Bud blast — Flower buds turn brown and fail to open, caused by Pycnostysanus azaleae transmitted by leafhoppers. Control leafhoppers with insecticide in late summer.
  • Waterlogging — Fibrous roots rot quickly in poorly drained ground. Improve drainage before planting; raise the planting level slightly if drainage is borderline.

Companion plants

Azalea 'Gibraltar' pairs well with Camellia japonica, Pieris japonica, Ferns (Dryopteris), and Erythronium. These are species with similar light and water needs, so you can group them in the same room or on the same shelf and water as a batch.

Propagation

Take semi-ripe cuttings 7-10 cm long in summer, dipping in rooting hormone and placing in ericaceous cutting compost under humidity. Layering flexible stems into acidic compost in summer is the easiest method. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Azalea 'Gibraltar' is toxic to pets. The ASPCA lists Rhododendron (including azaleas) as toxic to dogs, cats, and horses. All parts contain grayanotoxins, which can cause vomiting, drooling, weakness, hypotension, and cardiac arrhythmia even in small quantities. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Azalea 'Gibraltar' care — frequently asked questions

What is the common name for Rhododendron 'Gibraltar'?

Rhododendron 'Gibraltar' is most commonly called Azalea 'Gibraltar', but it is also known as Gibraltar Azalea, Knap Hill Azalea, Deciduous Azalea 'Gibraltar'. The names refer to the same species, so care instructions for Azalea 'Gibraltar' apply identically to anything sold as Gibraltar Azalea.

How much light does azalea 'gibraltar' need?

Azalea 'Gibraltar' grows best in bright indirect light (just back from a sunny window). Thrives in dappled shade or partial shade with some morning sun. Avoid intense afternoon sun, which causes petal scorch and bleaching. Under a light tree canopy is ideal.

How often should I water azalea 'gibraltar'?

Water azalea 'gibraltar' deeply once or twice a week in dry weather; keep consistently moist year-round. Rhododendrons and azaleas are sensitive to drought and waterlogging alike. Use soft water where possible — hard, alkaline tap water can raise soil pH over time. Never let the root ball fully dry out. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is azalea 'gibraltar' toxic to cats and dogs?

Azalea 'Gibraltar' is toxic to pets. The ASPCA lists Rhododendron (including azaleas) as toxic to dogs, cats, and horses. All parts contain grayanotoxins, which can cause vomiting, drooling, weakness, hypotension, and cardiac arrhythmia even in small quantities.

What USDA hardiness zone does azalea 'gibraltar' grow in?

Azalea 'Gibraltar' is rated for USDA zone 5-8 and RHS hardiness H6. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Azalea 'Gibraltar' deep-dive guides

Every aspect of azalea 'gibraltar' care, each with its own calibrated guide:

Featured in these plant shortlists

Azalea 'Gibraltar' qualifies for 6 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Azalea 'Gibraltar' is also known as Gibraltar Azalea, Knap Hill Azalea, and Deciduous Azalea 'Gibraltar'.