Overview of Rheum L.
Rheum L. is a genus of perennial flowering plants that belongs to the family Polygonaceae. The plants are known for their attractive foliage and are distributed across Asia, Europe and North America. Rheum L. comprises of approximately 60 species of plants, many of which are used for medicinal purposes. The plants are commonly referred to as rhubarb.
Appearance of Rheum L.
Rheum L. plants vary in size and appearance depending on the species. Generally, the plants have large, alternate leaves that can grow up to 3 feet in diameter and are typically reddish-green in color. The stem of the plant is long and thick, with an upright growth habit, and can reach up to 8 feet tall. The flowers appear in long, spiky panicles that grow at the top of the stem and range in color from white to cream, and are often lined with a pink or red hue.
Uses of Rheum L.
Rheum L. plants are highly valued for their medicinal properties. The roots of the plants are used in traditional Chinese medicine and Western herbalism to treat a variety of ailments, including digestive disorders, constipation, inflammation, and arthritis. The plants are also eaten as a food in some parts of the world, with the leaf stalks often used in desserts or savory dishes. Additionally, Rheum L. is used in cosmetics and dye-making due to the presence of anthraquinones in the plants that provide a red pigment.
Common Names of Rheum L.
Rheum L. is commonly referred to as rhubarb in English-speaking countries, with the word “rhubarb” derived from the Latin “rhabarbarum,” which means “root of the barbarians.” In other languages, the plant is referred to by varying names, for example, in Chinese, it is known as dàhuáng while in Russia, it is called rabarber.
Other common names for Rheum L. plants include pie plant, garden rhubarb, medicinal rhubarb, and ornamental rhubarb.
Light Requirements
Rheum L. requires full sunlight to grow properly. It should receive at least six hours of direct sunlight every day. The plant may suffer if grown in low light conditions.
Temperature Requirements
Rheum L. thrives in cool to temperate conditions. The plant grows best in temperatures ranging from 4°C to 24°C (40°F to 75°F). The optimal temperature range is between 10°C to 18°C (50°F to 64°F). Temperatures that are too high or too low can cause the plant to wilt or die.
Soil Requirements
Rheum L. prefers moist, well-drained soils rich in organic matter. The ideal soil pH is between 5.5 to 6.5. The plant can tolerate a slightly alkaline soil up to pH 7.5. The soil should have excellent drainage to prevent waterlogging, which can cause root rot. Adding compost or aged manure can help improve soil texture and fertility.
Cultivation Methods
Rheum L., generally referred to as rhubarb, requires fertile and well-draining soil to grow well. You can cultivate this plant by using root divisions rather than planting from seeds. The site where you grow the plant must have ample sun exposure, preferably six hours of full sunlight. This plant is tolerant of low temperatures, and you can set it out from late winter to early spring when the soil has warmed up to 10 °C or more.
Watering Needs
You must water Rheum L. regularly to avoid moisture stress, which is common in a dry climate. A constantly moist soil is ideal for this plant, but it's crucial to avoid waterlogged soil as the plant may rot. You can check the soil moisture content by inserting a finger into the soil, and if it feels dry, it's time to water. In the absence of rainfall, you can irrigate the plant by flooding the ground around it as it's a deep-rooted plant.
Fertilization
It's vital to fertilize Rhubarb in the early spring season with plenty of well-rotted farmyard manure as it’s a heavy feeder. Additionally, you can top-dress the plant with potassium-rich fertilizers in early autumn. Nitrogen-rich fertilizers and fresh manure could hurt the plant roots. Too much nitrogen could lead to growth of lush foliage at the expense of the rhizome.
Pruning
Pruning Rheum L. will allow enough air circulation and soil moisture conservation, leading to vigorous plant growth. After harvesting the leaves, cut off the leaf stems near the ground using a sharp knife. The plant leaves will regrow in a few weeks. To maintain the plant’s productivity, remove any flowers that develop since this may affect leaf growth and quality. When the plant reaches four or five years, you can dig it out, divide the rhizomes, and replant with the new divisions in a different location.
Propagation of Rheum L.
Rheum L. is commonly known as the rhubarb plant, which belongs to the family of Polygonaceae. It is a herbaceous perennial plant and mainly propagated by using its crown or root cuttings.
Propagation by Crown
The most common method of propagating Rheum L. is through crown division or separation. Crown is the upper part of the root system, which is located at the soil surface. This part should be divided and replanted every four to five years for better growth and yield.
Crown division should be done in early spring or late autumn before the development of new leaves. For better results, the selected crown should have at least three to four buds with a well-developed root system. To separate the crown, the plant should be uprooted carefully and excess soil should be washed off. Then, using a sharp and sterilized tool, the crown should be divided into pieces, making sure that each part has enough buds with roots attached.
The separated crowns should be planted in well-prepared soil, with proper depth and spacing. The top of the crown should be placed at soil level, and the soil should be properly firmed and watered.
Propagation by Root Cuttings
Another method of propagating Rheum L. is through root cuttings. This method is practical when the plant is not yielding or the crown is unavailable.
Root cuttings should be taken in early spring when the plant is dormant. The selected root should be thick, mature, and free of disease or damage. The root should be cut into 2-3 inch pieces, making sure that each piece has at least one bud and a well-developed root system.
The root cuttings should be planted in well-drained soil, with proper spacing, and the top of the cutting should be just above the soil surface. Water the cuttings immediately and keep the soil moist. The cuttings will develop roots and new shoots in a few weeks.
Disease and Pest Management for Rheum L.
Rheum L., commonly known as rhubarb is a perennial plant widely cultivated for its edible stalks. While it is known for its culinary use, it is not immune to diseases and pests that can threaten its growth and quality. Here are some common diseases and pests that affect the plant and ways to manage them:
Diseases
Crown Rot: This disease is caused by a fungus called Phytophthora cactorum which attacks the crown and roots of the plant. The infected plants have stunted growth, wilted leaves, and sometimes no production of stalks at all. To manage the disease, avoid planting in areas with poor drainage and use resistant cultivars. Avoid wetting the leaves or stem while watering and remove the infected plants to prevent spore dispersal.
Fungal Leaf Spot: The disease is caused by the fungus Ascochyta rheum which causes circular or irregular brown-colored spots on the leaves. It can be managed by keeping the area weed-free, providing adequate space for the plants to grow, and practicing crop rotation. Fungicides like copper-based sprays can also be used to prevent the spread of the disease.
Pests
Rhubarb Curculio: The Rhubarb Curculio is a small brown-colored beetle that causes holes in the leaves and stem of the plant. The larvae of the beetle burrow into the stalks, causing damage that reduces marketability. Pesticides like pyrethrin can be used for management during the early stages of infestation.
Rhubarb Aphids: These aphids feed on the sap of the plant, causing the leaves to curl and contort. They are small, yellow, and green-colored insects that form dense colonies on the underside of the leaves. Use insecticidal soap or neem oil to manage the infestation. They can also be naturally controlled by introducing beneficial insects like ladybugs.
Having a healthy and vibrant Rhubarb plant requires careful management of diseases and pests. Always keep a close eye on the plants and be ready to take measures when there is an infestation or disease break out to prevent it from spreading.
