Rhododendron maddenii
A fragrant species rhododendron, Rhododendron maddenii is grown for its large, white trumpet flowers and powerful scent. The flowers, sometimes flushed pink on the outside of the tube, appear later than most rhododendrons, often into late spring, and carry a rich perfume on warm days. The shrub is open and somewhat upright, with handsome scaly, deep green leaves.
Because of its scent, Maddenii is best sited where people pass close by, near a path, a door, or a sheltered patio. It can be grown against a warm wall or kept in a large container moved under cover for winter. This rhododendron suits cottage gardens, courtyard plantings, and sheltered coastal gardens, and its later flowering extends the rhododendron season.
Plant in dappled shade in free-draining, acidic soil enriched with compost or leaf mould. Maddenii is frost tender, so it is best in warm, sheltered, and coastal gardens and is not suited to frost-prone inland districts such as Central Otago or inland Southland without protection. Rhododendron foliage is toxic to cats and dogs if eaten in quantity.
Maddenii grows into a larger shrub over time, reaching around 2 m or more, and takes well to pruning after flowering.
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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