Rhododendron dauricum: A Cold-Resistant Gem for Your Garden

The Rhododendron dauricum is a cold-resistant species within the Rhododendron family. It bears vibrant and fragrant flowers that can be planted individually or in clusters, forming attractive landscapes, and is also an excellent choice for rock gardens.

With a well-developed root system that spreads out in various directions, it is a great plant for soil and water conservation, and can be used to make bonsai or root carvings.

I. Basic Introduction

The Daurian Rhododendron (scientific name: Rhododendron dauricum L.) is a semi-evergreen shrub from the Rhododendron genus, reaching up to 2 meters in height with numerous branches.

Its leaves are nearly leathery, elliptical or oblong, with blunt ends. The upper surface is dark green and the underneath is pale green, with a leaf stalk that is slightly hairy. The flowers, which bloom before the leaves, grow in umbels at the top of the branch or in a false terminal position.

The corolla is wide and funnel-shaped, pink or purple-red, with purple-red anthers and pistils. The fruit is an oblong capsule. It flowers from May to June and bears fruit in July.

It grows in mountainous larch forests, under birch trees, or along the forest edges. The Daurian Rhododendron is not only used for ornamental purposes, but its leaves, which contain essential oils and coumarin, can be used to extract aromatic oils and produce fragrances.

Additionally, it has medicinal properties; it is cold and bitter in nature and is used to treat acute and chronic bronchitis by suppressing coughs and eliminating phlegm. The stem, branches, and fruit contain tannins and can be used to produce glue.

II. Growth and Distribution

Growing Environment

It grows in mountainous larch forests, under birch trees, or along the forest edges.

Distribution Range

It is found in Japan, Korea, and Russia.

III. Morphology and Characteristics

This semi-evergreen shrub grows between 0.5 and 2 meters tall, with numerous branches. The young branches are thin and curved, covered with soft hairs and scales.

The leaves are nearly leathery, elliptical or oblong, 1-5 cm long and 1-1.5 cm wide, with blunt ends. Sometimes, the base is broad wedge-shaped.

The upper surface is dark green with scattered scales, while the underneath is pale green and densely covered with scales of varying sizes. The leaf stalk is 2-6 mm long and slightly hairy.

The flowers grow in umbels at the top of the branch or in a false terminal position, with 1-4 flowers blooming before the leaves.

The flower stalk is 2-8 mm long, and the corolla is wide and funnel-shaped, 1.3-2.3 cm long, pink or purple-red, usually with soft hairs on the outside and no scales. The ovary has 5 compartments and is densely covered with scales. The pistil is purple-red, smooth, and longer than the corolla.

The fruit is an oblong capsule, 1-1.5 cm long and about 5 mm in diameter, splitting at the top into 5 sections. It flowers from May to June and bears fruit in July.

IV. Cultivation Method

Transplantation: Seedlings and cuttings can be transplanted in the same year. Water the seedbed thoroughly a day in advance. When lifting the seedlings, do not damage the roots. Choose high-quality seedlings without pests or diseases for transplantation.

Water thoroughly to facilitate normal growth of the seedlings, while preventing pests and diseases, and apply fertilizer, weed, and loosen the soil.

Planting: Seedlings and cuttings usually grow to the 3rd year and can be planted directly. Wild seedlings can also be transplanted. Usually, this is done after the leaves fall in autumn until the buds sprout in spring.

The seedlings can be row-planted or hole-planted. Apply enough base fertilizer and water thoroughly a day in advance. Do not damage the main root when lifting the seedlings.

When row planting, the row spacing should be 70-80 cm, and the plant spacing should be 20-30 cm. When hole planting, the hole spacing should be 60-70 cm, with 2-3 seedlings planted in each hole.

When planting, put the seedling into the hole. When the filling soil is about half, gently lift the seedling so that the root system is well spread, then fill the soil and tread it firmly, and then water the seedling.

Half a month after planting, water once more to improve the survival rate. Pay attention to weeding and loosening the soil in the summer and autumn rainy season, and prevent pests and diseases.

V. Methods of Propagation

The propagation methods used are seeding and cutting.

Seeding: Fill a flower pot with sandy loam mixed with peat soil, then mix the seeds with fine sand and sow them in the pot. Cover the pot with a piece of glass to maintain a temperature of 15-20℃, and sprinkle water to keep the soil moist.

After about two weeks, the seeds will start to germinate. Once they grow three true leaves, they can be transplanted.

Cutting: In May or June, cut robust new branches, keep the top leaves, and cut the branches into 10-20 cm cuttings. Insert them diagonally or vertically into the nursery bed, and maintain the bed’s temperature and humidity. After about a month, new roots will start to grow.

Tissue Cultivation:

Collecting and Processing of Materials: Choose robust, disease-free wild Rhododendron dahuricum plants and cut 50 cm long branches for hydroponic treatment.

When the stem grows to 3 cm, cut it off, rinse it with tap water for 2 hours, and then sterilize it on a sterile operation table.

Specific Method of Sterilization: Rinse the rinsed stems with sterile water once, then put the stems in 70% alcohol for 10 seconds to sterilize. Remove the stems, rinse them with sterile water three times, then use 3% sodium hypochlorite to sterilize for 40 seconds.

Rinse with sterile water three more times, then use sterile filter paper to dry the water on the stem surface. Use sterile scissors to cut off the part of the stem that has been oxidized by the disinfectant, and the process is complete.

Induction and Propagation of Adventitious Buds: After sterile treatment of the materials, inoculate them into the adventitious bud induction medium WPM1 and cultivate at a temperature of 25℃, 16 hours of daily light, and a light intensity of 40 micromoles/(square meter·second).

After 20 days, adventitious buds can be induced, continue to place in the medium WPM1 for adventitious bud propagation.

Induction of Adventitious Bud Elongation: Cut the callus tissue with adventitious buds into pieces and put them into the adventitious bud elongation medium WPM2.

Cultivate under the conditions of 25℃, 16 hours of daily light, and a light intensity of 40 micromoles/(square meter·second). After about 20 days, the adventitious buds will elongate 1-2 cm.

Rooting of Cluster Buds: Inoculate the stems with 1-2 cm of cluster buds into the rooting medium WPM3. Cultivate at a temperature of 25℃, 16 hours of daily light and a light intensity of 40 micromoles/(square meter·second) for 20-25 days, and the base of the bud will start to root. After 40 days of cultivation, the average root length is 3.5 cm.

Transplanting Seedlings: After the seedlings have been hardened for two days, transplant the plants with roots longer than 2 cm to a greenhouse for cultivation.

After transplantation, the survival rate of the seedlings is 100%. Before hardening, add a small amount of sterile water to the bottle of the tissue-cultured seedling after rooting, and place it in the greenhouse for hardening.

VI. Disease Control

Wilt Disease

This is a significant nursery disease for Rhododendron xinganense. The pathogen enters through stomata and wounds at the root neck of seedlings and cuttings, causing the seedlings’ root neck to constrict.

Subsequently, the leaves turn yellow, and the plants die off abruptly. The control method is to use sterilized soil for seeding, maintain ventilation and air permeability in the nursery, enhance seedling management, and irrigate with a 70% carbendazim solution diluted 500-800 times at the onset of the disease.

Black Spot Disease

This primarily affects the leaves. In the early stages of the disease, the leaves start to show chlorotic spots and fall off from bottom to top. The control method is to strengthen management, provide adequate ventilation and air permeability, increase scattered light, and irrigate with an 800-fold solution of thiophanate-methyl.

Leaf Swelling Disease

In the early stages, the leaves show chlorotic spots, thicken, and swell. Later, the disease spots turn brown and die off. The control method is to strengthen field management, plant disease-resistant varieties, and remove infected leaves promptly.

Potted rhododendrons should be placed in ventilated and well-lit areas, and a solution of 70% thiophanate-methyl or 70% carbendazim diluted 1,000 times should be sprayed at the onset and peak of the disease.

Dieback Disease

In the early stages, the new shoots and buds of the affected rhododendrons wilt and thin out, with the tops curving downwards in a hook shape. Subsequently, the new shoots lignify and die standing up.

The control method is to use crop rotation, avoid planting too densely, and avoid planting for two consecutive seasons. Before planting, disinfect the soil with fungicides like carboxin, control soil moisture, and fumigate with 2.5% carbendazim when not infected.

At the onset of the disease, spray with a solution of 400 times diluted alum.

Red Spider Mites

The adults primarily damage the backs of leaves, petioles, and main veins, causing the affected leaves to scorch and drop off, severely affecting their ornamental value.

The peak period is from July to September. The control method is to first remove or burn off the infected leaves, and in severe cases, spray a 0.01%-0.025% solution of 40% chlorfenapyr.

Armyworms

They parasitize the backs of leaves, causing the affected leaves to exhibit brownish-yellow spots. Spray a 50% zinc phosphide solution every 7-10 days, for a total of 2-3 times.

VII. Value and Others

Primary Value

Medicinal Use

Leaves or leafy twigs are used to treat indigestion, cold diarrhea, dry cough, lung disease, kidney cold, edema, physical weakness, and sperm deficiency.

Leaves are used to treat chronic bronchitis, coughing, high blood pressure, arthritis, difficulty urinating, alopecia, and stomach spasms.

The root is used to treat enteritis, acute bacillary dysentery, and more, demonstrating its medicinal value. Its flowers also have calming and sleep-inducing effects. The leaves can be used in medicine to treat coronary heart disease, chronic bronchitis, bronchial asthma, and other diseases.

Horticulture

Xing’an Rhododendron is among the more cold-resistant species of the rhododendron family, with its vibrant and fragrant flowers being deeply loved by people. It can be planted individually or in groups to create beautiful landscapes and is a top-notch material for rock garden construction.

The Xing’an Rhododendron has a well-developed root system, making it an excellent plant species for soil and water conservation. Its intertwined roots can be used to create bonsai and root carvings.

Its bright, eye-catching flowers bloom early, adorning the cold mountains of early spring in the North, bringing delight and a sense of spring. With a long blooming period, it is a beautiful ornamental and nectar-producing plant.

Therefore, the Xing’an Rhododendron can be widely used in medicine, landscaping, ecology, crafts, and as a street tree.

Plant Culture

Every May, the fiery red flowers of the Xing’an Rhododendron bloom proudly, covering the mountains and forests. The Little Xing’an Range is filled with colors, competing in beauty and splendor, earning the title of “Sea of Rhododendron Flowers”.