Rhododendron Blue Diamond
Compact, aromatic, and generous with flower, Rhododendron 'Blue Diamond' is one of the most popular dwarf rhododendrons for a small garden. Around October it covers itself in masses of small violet-blue flowers, held above tiny leaves that release a light scent when brushed. The habit is upright and densely branched, building slowly into a neat, well-furnished shrub.
This is a rhododendron that earns its place in tight spaces. It suits the front of a border, a rockery, a woodland edge, or a container on a patio, and groups well for a drift of spring colour. Blue Diamond fits cottage gardens, woodland schemes, and shade or Japanese-influenced plantings, and unusually for a rhododendron it tolerates more sun, provided the soil stays moist.
Plant in dappled shade or morning sun in free-draining, acidic soil enriched with compost or leaf mould. Keep the shallow roots cool and damp with annual mulching and water through dry spells. Rhododendron foliage is toxic to cats and dogs if eaten in quantity.
Blue Diamond reaches around 1 to 1.2 m tall and slightly less wide at maturity, growing slowly and staying compact.
Trimming: Rhododendrons need very little pruning. After flowering in spring, remove any dead, damaged, or crossing stems and lightly shape to keep the form neat. Avoid cutting hard into old, bare wood, as rhododendrons can be slow to reshoot from it.
Deadheading: Deadheading is not essential. If you have time, snap off the spent flower trusses by hand once flowering finishes, which tidies the plant and channels energy into next season's growth rather than seed. Take care not to damage the new buds forming just below.
Fertilising: Feed in early spring with a fertiliser made for acid-loving plants, such as rhododendron, azalea, and camellia food. A second light feed after flowering supports new growth. Avoid lime and high-nitrogen lawn fertilisers, which the shallow roots dislike.
Watering: Keep the soil evenly moist, especially through the first two summers and in dry spells. The shallow, fibrous roots dry out quickly, so water deeply and mulch with bark or leaf mould to hold moisture. Rainwater is better than hard tap water where possible.
Pest Control: Thrips are the main concern in NZ, silvering the upper leaf surface in warm, dry weather, while two-spotted mite and scale insects can also appear. Treat with horticultural oil, keep plants well watered, and improve airflow around the foliage.
Disease Management: Most problems trace back to soil and drainage. Phytophthora root rot causes wilting and dieback in wet, heavy ground, so plant in free-draining soil or a raised position. Petal blight can mark the flowers in warm, humid spring weather; remove affected flowers promptly.
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