Shrub (ericaceous)
How to grow azaleas
Rhododendron (Azalea group)
Azaleas are the small-leaved, small-growing end of the rhododendron family. Plant one in September to October or March to April in acid, humus-rich soil (pH 4.5 to 6.0) or a pot of ericaceous compost, with the top of the rootball level with the surface. Evergreen Japanese types want part shade; deciduous types take more sun and give scent and autumn colour. Keep the roots moist with rainwater from July to September, when next year's flower buds form.
- Hardiness
- Fully hardy (deciduous types especially)
- Position
- Part shade
- Soil
- Acid, humus-rich, moist
- Ideal pH
- 4.5 to 6.0
- Water
- High, keep moist; rainwater
- Feeding
- Light feeder
Sowing and planting azaleas
WhenPlant Sep to Oct or Mar to Apr; flowers Apr to Jun
Starting off
Plant pot-grown stock Sep to Oct or Mar to Apr; soak dry rootballs in a bucket for an hour first. Propagate evergreen types by 5 to 8 cm semi-ripe cuttings in Jul to Aug at 18 to 20°C under a lid, rooting in 6 to 8 weeks; deciduous types by softwood cuttings in May to Jun or by layering in Apr. Seed from deciduous azaleas sown on moist ericaceous compost in Feb at 15°C germinates in 3 to 4 weeks but takes 4 to 5 years to flower.
Spacing and planting
Evergreen Japanese azaleas spread 60 to 120 cm by 60 to 100 cm; deciduous Ghent, Knap Hill and Exbury types reach 1.5 to 2.5 m by 1.5 m. Plant 60 cm or 1.2 m apart respectively, in a wide shallow hole with the rootball top level with the surface. Evergreen types make superb plants for a 30 to 40 cm pot of ericaceous compost.
Varieties worth growing
- 'Hinomayo'
- Evergreen Kurume azalea smothered in small clear pink flowers in April and May; dense, slow and about 80 cm tall, so it suits a pot.
- 'Johanna'
- Evergreen with deep red flowers and glossy leaves that turn bronze-red in winter; one of the toughest of the Japanese types.
- 'Palestrina'
- Evergreen, white flowers with a faint green eye in May; a cool colour for a shaded corner.
- Rhododendron luteum
- The yellow deciduous azalea: honeysuckle scent in May, strong red and orange autumn leaves, and it puts up with more sun and poorer soil than the evergreens. It is listed on Schedule 9 of the Wildlife and Countryside Act, so keep it in the garden and never plant it out in the wild.
- 'Gibraltar'
- Knap Hill deciduous hybrid with frilled flame-orange trusses in May; reaches about 1.5 to 2 m.
Azaleas month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do. Check pots are draining and not standing in water.
- February
Sow seed of deciduous azaleas on ericaceous compost at 15 °C. Test the soil pH before ordering plants.
- March
Plant. Light feed. Cut leggy old deciduous plants back to 30 cm if they need renovating.
- April
Plant. Mulch 5 cm with leaf mould or pine needles. Fleece buds on frosty nights. Layer low branches.
- May
Flowering. Pick off azalea galls. Softwood cuttings of deciduous types.
- June
Deadhead deciduous types and tip-prune evergreens straight after flowering. Second light feed.
- July
Water with rainwater in dry spells: next year's buds are forming. Semi-ripe cuttings of evergreen types.
- August
Keep watering. Vine weevil nematodes on pots at the end of the month.
- September
Plant from now while the soil is warm. Keep watering if dry.
- October
Plant. Autumn colour on deciduous types. Rake up mildewed leaves.
- November
Nothing to do. Raise pots on feet for the winter.
- December
Nothing to do.
Feeding azaleas
A light feeder with fine, shallow roots that scorch easily. Acid soil, leaf mould and rainwater come first, so give any azalea fertiliser at half rate and never lime.
Low, ericaceous feed only.
Feeding plan
March, beds
Fruit & Vegetable Fertiliser 4-5-6
Half the label rate: 35 to 55 g/m² scattered over the root area and watered in. That is about 30 to 45 g for a plant 1 m across (0.8 m²). This is not an ericaceous feed, so it does nothing to hold the pH down.
April
Leaf mould, composted bark or pine needles
A 5 cm mulch over the root area, kept just clear of the stems. Do not fork it in: the roots are at the surface.
June, after flowering
Fruit & Vegetable Fertiliser 4-5-6
25 g/m², half the lower label figure for a second dressing, and nothing after June. Skip it for a plant growing and flowering well.
March and June, pots
Fruit & Vegetable Fertiliser 4-5-6
1 to 2 g per litre of compost on the surface, half the label top-dress rate: 15 to 30 g for a 30 cm pot (about 15 litres), 30 to 60 g for a 40 cm pot (about 30 litres).
Autumn or early spring, only if a test shows pH above 6
To lower the pH by one unit: 55 g/m² on sand, 110 g/m² on loam in two doses six months apart, 175 g/m² on clay in three doses; never more than 80 g/m² in one go.
Dr Forest has no ericaceous feed. The plan uses the Fruit & Vegetable Fertiliser 4-5-6 at half the label rate as the nearest fit; it is not an ericaceous feed and does not acidify. Mycorrhizal Fungi Powder is not recommended for ericaceous plants.
Signs to watch
New leaves pale yellow with green veins
Iron locked out by lime or hard water
Rainwater, sulphur chips, ericaceous feed with chelated iron
Older leaves yellow between the veins and drop early
Magnesium short on acid sand
Epsom salts spray at 20 g per litre in Jun
Few flowers but lots of leaf, or buds dropping in Mar
Excess nitrogen, or drought in Aug to Sep while buds formed
Stop feedin
Pests, diseases and problems
Pale green, fleshy swellings on leaves or flowers of evergreen azaleas in spring, later turning white and powdery
Azalea gall, a fungus
Pick the galls off and bin them before the white bloom of spores appears. The plant is not harmed otherwise and no spray is needed.
Notches eaten from leaf edges; a pot plant wilts and comes loose, with white C-shaped grubs among the roots
Vine weevil: adults notch the leaves, the grubs eat the roots
Water nematodes into the compost in late August or September and again in April, when the compost is above 5 °C. Pick adults off by torchlight on summer evenings.
Flowers develop watery spots, then collapse into a slimy brown mess that stays stuck to the plant
Petal blight, a fungus that spreads in mild, wet weather at flowering
Pick off and bin affected flowers promptly, water at the base and never over the blooms, and renew the mulch each spring to bury fallen spores.
White powdery coating on the leaves of deciduous azaleas from midsummer
Powdery mildew, worse on dry-rooted plants in still air
Water the roots deeply in dry spells, mulch, and rake up the fallen leaves in autumn. Thin crowded neighbours to let air through.
Open flowers and fat buds turn brown overnight in April or May
Late frost, worst where early sun thaws frozen buds quickly
Throw fleece over the plant on forecast frost nights and avoid east-facing spots. Move pots against a house wall.
Whole plant wilts and dulls in wet ground, roots brown and rotten
Phytophthora root rot in waterlogged soil
No cure. Remove the plant and its soil, improve the drainage or build a raised bed, and replant shallowly.
Pruning
Pruning and care
Flowers on last year's wood, so prune only straight after flowering in May to Jun: tip-prune evergreen types lightly for bushiness and deadhead deciduous types by pinching the spent truss. Leggy old deciduous plants can be cut to 30 cm in Mar and recover over 2 years. Mulch 5 cm with leaf mould or pine needles each Apr and water the roots in Jul to Sep when buds form. Protect the swelling flower buds of
Good to knowEssentially a small rhododendron; deciduous types give autumn colour. Keep moist.
Growing azaleas in pots
Evergreen Japanese azaleas are among the best shrubs for pots; deciduous types get too big after a few years. Use a 30 to 40 cm pot with ericaceous compost, ideally a loam-based one that holds its structure, and set the rootball level with the surface. Water with rainwater whenever you can: hard tap water slowly raises the pH and the leaves yellow. The compost must never dry out between July and September. Stand the pot in part shade, raise it on feet in winter, top-dress with fresh ericaceous compost each March and repot every two to three years.
Azaleas: common questions
What is the difference between an azalea and a rhododendron?
Botanically none: azaleas are rhododendrons. In gardens the name is used for the smaller plants with small, thin leaves, either evergreen Japanese types under about 1.2 m or deciduous types that lose their leaves in autumn. They want the same acid soil and shallow planting.
Why are my azalea leaves turning yellow?
Usually the soil or the water is too alkaline, which locks up iron so the newest leaves yellow between green veins. Test the pH, water with rainwater, acidify with sulphur or move the plant into ericaceous compost. Yellowing all over on a wilting plant points to waterlogged roots instead.
When should I prune an azalea?
Straight after flowering, in May or June, and only lightly. Azaleas flower on last year's wood, so pruning later in the summer removes the buds for next spring. Most need nothing more than the removal of dead or straggly shoots.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.
- How to grow rhododendronsRHS
- Vine weevilRHS
- Wildlife and Countryside Act 1981, Schedule 9legislation.gov.uk