Rhododendron aureum: The Enchanting Golden Wonder

The Rhododendron aureum, also known as the Golden Rhododendron or Leather Rhododendron, is a low-growing evergreen shrub in the family Ericaceae, typically reaching heights of 10-50 cm.

Its stem grows horizontally with ascending side branches that have persistent bud scales. The leaves are leathery, usually grouped in clusters of 4-5 at the end of the twigs, and are lanceolate or ovate-oblong in shape.

The upper surface of the leaves is a dark green color, while the underside is a lighter shade of green. The plant produces terminal umbellate inflorescences with 5-8 flowers.

The corolla is bell-shaped and pale yellow, with one lobe featuring red spots. The blooming period is from May to June, and the fruiting period is from July to September.

The Golden Rhododendron is native to regions in China, Russia, Mongolia, North Korea, and Japan, and can be found in alpine grassland zones or moss layers at elevations of 1000-2500 meters.

This plant is highly valued for ornamental purposes due to its beautiful form and year-round verdant foliage. Its thick, glossy, and bright green leaves are part of what gives it the name ‘Leather Rhododendron’.

However, the species’ distribution is narrow, with small wild populations, and its habitat is under threat from degradation.

I. Common Varieties

This species is a small shrub characterized by persistent bud scales and leathery leaves, which are hairless on both surfaces. Its yellow flowers make it easy to distinguish from other species.

II. Growth and Distribution

The Golden Rhododendron thrives in alpine grassland zones or on moss layers at elevations of 1000-2506 meters. The type specimen was collected from eastern Siberia.

III. Morphology and Characteristics

The Golden Rhododendron is an evergreen dwarf shrub, 10-50 cm in height. The stem grows horizontally, with ascending side branches that have persistent bud scales. The leaves are leathery, typically clustered in groups of 4-5 at the tip of a twig.

They are lanceolate or ovate-oblong in shape, 2.5-8 cm long and 1-3.5 cm wide, with a blunt or rounded tip, a wedge-shaped base, and slightly recurved margins. The upper surface is dark green, slightly wrinkled, hairless, with the midvein sunk and 8-13 pairs of lateral veins slightly sunk.

The undersurface is pale green, hairless, with the midvein protruding, sometimes with remnants of young hairs, and the lateral veins slightly protruding. The leaf stalk is 5-10 mm long, with a groove on the upper side and a round shape on the underside.

The terminal umbellate inflorescence has 5-8 flowers, with a total axis length of about 1 cm. The pedicel is erect, about 3 cm long, sparsely covered with red fluff, located within the persistent bud scales and bracts.

The calyx is small, about 2 mm long, with 5 small teeth and covered with coiled hairs. The corolla is bell-shaped, 2.5-3 cm long, pale yellow, 5-lobed, with lobes nearly round and slightly unequal in size.

One lobe features red spots, measuring 1-1.2 cm long and 1.5-1.8 cm wide, with a slightly missing tip. There are 10 stamens that are unequal in length, 1.2-2.3 cm long, with the filament base covered with white soft hairs.

The anthers are elliptical, pale brown, and 2 mm long. The ovary is ovate-globular, 5 mm long, densely covered with rust-colored woolly hairs. The style is 2.5 cm long and hairless, with a small stigma that is shallowly 5-lobed.

The fruiting inflorescence is erect, with a pedicel 4.5-6 cm long, sparsely covered with soft hairs. The capsule is cylindrical, 1-1.4 cm long and 5-6 mm in diameter, 5-lobed, and more or less woolly.

The blooming period is from May to June, and the fruiting period is from July to September.

IV. Living Habits

Rhododendrons originate from high-altitude regions, thrive in cool, moist climates and don’t tolerate harsh, hot, and dry conditions. They require acidic soil with a pH of 5.5 to 6.5 that is rich in humus, loose, and moist.

Some species and horticultural varieties are highly adaptive, can withstand drought, and can grow in soil with a pH of 7 to 8. However, they struggle to grow in heavy or poorly drained soils.

Rhododendrons need a certain amount of light, but they can’t handle direct sunlight. During the summer and fall, they should be shielded from the harsh sun by deciduous trees or shade structures, and the ground should be regularly sprayed with water.

Rhododendrons typically sprout in spring and fall, with spring being the dominant season. They grow best at temperatures of 15-20°C, bloom from March to May, and are tolerant of pruning.

Generally, pruning is done before May, and the new shoots formed can all produce flower buds within the year. Late pruning can affect blooming.

V. Cultivation Methods

Fertilizer and Water Management

Rhododendrons require acidic soil to grow and develop. As most soils in the north are alkaline, the potting soil should be a mixture of decomposed pine needle soil and other humus soils.

Rhododendrons have fine, hair-like root systems and need a specific concentration of fertilizer and water quality. When fertilizing, follow the principle of timely and moderate application, and apply thin fertilizer frequently.

Apply phosphate once a month before blooming in the spring to promote the growth of leaves and buds. After flowering, apply a mixed fertilizer of nitrogen and phosphorus 1-2 times.

During the bud formation period in September and October, apply phosphate 1-2 times. During the growth and blooming period, rhododendrons need more fertilizer and water.

In the dormant winter and slow-growing summer, control the amount of fertilizer and water to prevent root rot. Rhododendrons like a moist and cool environment. The northern climate is dry, so water and spray mist timely to maintain high air humidity.

Watering with alum water and rainwater is best. If using tap water, add a small amount of ferrous sulfate and vinegar. You can also add pieces of watermelon or tomato to improve the soil quality and the quality of the flowers.

Shaping and Pruning

To make the plants bloom more abundantly, rhododendrons are often pinched to stimulate new branches. For crowded flower clusters that affect the shape of the flowers, thin the buds early.

This not only makes the current year’s flowers bigger and brighter in color but also benefits the growth and flowering of the plants the following year. Rhododendrons have strong budding power.

Branches that seriously affect the growth and development of the plants and reduce their ornamental and commercial value need to be pruned. Pruning is generally done after the flowers fade in spring and in autumn.

Cut off dead branches, slanting branches, overgrown branches, diseased branches, and some crossing branches to avoid nutrient consumption and make the whole plant bloom fully.

Flowering Control

Rhododendrons undergo flower bud differentiation in autumn. Through refrigeration and heating treatments, the flowering period can be artificially controlled.

To make rhododendrons bloom early, move them to a greenhouse for cultivation, control the temperature at 20-25°C, and frequently spray water on the branches and leaves to maintain a relative humidity of over 80%. After a month and a half, they can bloom.

To delay the flowering of rhododendrons, keep the budding rhododendrons in a low-temperature state, maintain a temperature of 2-4°C, water when the pot is dry, move them outside in summer and autumn, and they can bloom after 2 weeks.

Creating Bonsai

For the leatherleaf rhododendron, it’s essential to maintain warmth and moisture. In spring, two-thirds of the dug-up stump should be buried in soil. After planting, ensure the soil is moist but not waterlogged.

Once the plant has stabilized and sprouted, gradually remove the sandy earth around the trunk. During the shaping process, regularly mist the foliage and trunk to increase air humidity, but avoid over-saturating the roots.

In particular, prevent waterlogging to avoid root rot. Shade the plant in summer to protect it from harsh sun exposure.

The leatherleaf rhododendron can be shaped into various bonsai forms such as upright, slanted, curved, twin-trunk, multi-trunk, exposed-root, cliff, rock-clasping, and water-land styles.

Seedlings propagated by cutting or layering can be shaped annually after 3-4 years of growth, typically before spring budding or during the summer or autumn growth period. Trimming is the primary shaping method, supplemented by wiring.

When shaping, follow the principle of shaping coarse parts first, then fine ones. Apply appropriate wiring to the main trunk and branches, and trim other branches. Rhododendron branches are fragile and prone to breaking, so handle with care.

If a branch breaks during the growing season, apply yellow mud to the wound, cover with plastic wrap, and it will heal quickly. Older rhododendron stumps are shaped by trimming, but some branches can also be wired.

To enhance aesthetic appeal, graft a high-quality rhododendron onto a robust, beautifully shaped, old white rhododendron stump. Depending on the stump’s condition, gradually remove some soil to expose the roots, creating an antique, vigorous look.

Leatherleaf rhododendrons prefer a warm, humid, semi-shaded environment with good ventilation. Place them in a brightly lit location for everyday care.

During the hot seasons of summer and early autumn, provide shade to protect from intense sunlight, which can scorch the leaves. However, avoid excessive shading to prevent the plant from becoming leggy and affecting blooming.

Keep the soil moist during the growing period, but avoid waterlogging. In rainy seasons, ensure proper drainage. When the air is dry, spray water on the plant and the surrounding ground to increase air humidity and prevent leaf desiccation.

To prevent the sun from scorching the fine roots on the surface of the potting soil, cover it with a layer of soft grass. Apply a thin, decomposed liquid fertilizer every 15 days.

To prevent yellowing disease, add a small amount of green vitriol to the fertilizer to maintain the leaves’ bright green color. During the bud stage, apply 1-2 doses of bone meal or superphosphate to enhance flower size and color.

During winter, move the plant to a sunny indoor location, maintaining a soil temperature above 0°C to prevent freezing, and control watering to keep the potting soil slightly moist.

After the annual flowering, trim the plant, removing diseased, dead, crossing, overlapping, weak, and leggy branches. Appropriately trim excessively long branches to maintain a beautiful shape and a reasonable distribution of branches, enhancing the plant’s growth.

Every 2 years, in spring or late autumn, repot the plant using slightly acidic, sandy soil rich in humus and fertility.

VI. Reproduction Method

The propagation of leatherleaf rhododendron can be achieved through methods such as layering, cutting, dividing, and grafting. You can also use rhododendron stumps that have grown for many years and have a unique and antique trunk to create bonsai.

They are often excavated and transplanted before the flowers fade in spring or late autumn and early winter, bringing much of the original soil with them. The main trunk and main roots should be appropriately pruned, cutting off branches that affect the shape, leaving lateral roots and fibrous roots.

For larger branches, they should be carefully examined and only removed if they do not contribute to the desired shape. They should first be planted in tile pots or underground to nurture the base, using well-draining sandy soil.

For stumps dug up in late autumn and early winter, they should be completely buried in sandy soil after planting, leaving only a small amount of branches exposed. After thorough watering, cover with a plastic bag.

VII. Disease Control

Leaf Swelling Disease

Before the onset of the disease, especially during the leaf expansion period, a Bordeaux mixture of 1:1:200 can be sprayed. Diseased leaves should be removed promptly.

Before budding, you can spray 0.3-0.5% of Bomei stone sulfur compound or 1:1:200 of Bordeaux mixture 2-3 times, usually every 7-10 days. After the disease, you can spray 65-80% of Daisen manganese zinc 500 times liquid or 0.3-0.5 Bomei stone sulfur compound 3-4 times, every 7-10 days.

Leaf Spot Disease

Leaf spot and brown spot diseases can be controlled effectively by spraying 70% methyl tobujin 1000 times liquid, 20% rust 4000 times liquid, 50% Daisen manganese zinc 500 times liquid from May to August, every 10 days, a total of 7-8 times. To prevent leaf yellowing, ferrous sulfate can also be applied.

Mite Disease

Affected young branches and leaf tips are covered with a dense layer of white or pink mite substance, sometimes leaf mites are produced, often caused by aphid puncture leaf infection.

The prevention and control methods include: while removing diseased leaves, spray copper sulfate-containing drugs; spray oxidized happy fruit emulsion oil or put furan directly in the pot to prevent aphids and other sucking pests.

VIII. Value and Others

The leaves of this species contain essential oils, which can be used as fragrance ingredients. The roots, stems, and leaves contain tannins, which can be used to make glue, and the leaves can also be used as a tea substitute.

Endangered species. This plant has large, beautiful leaves and is a rare evergreen ornamental plant in the northeast. It grows on alpine tundra and stony slopes, which is beneficial for soil and water conservation, playing an important role in maintaining ecological balance. In addition, it is also a germplasm resource for breeding.