Rhubarb (Rheum rhabarbarum)

Rhubarb (Rheum rhabarbarum) is a vegetable that’s usually prepared and eaten like a fruit, turned into pies, jams, jellies, and more. This cool-season crop, which is perennial in many areas, is grown for its fibrous leaf stalks that can make a wonderful tart treat. In addition, rhubarb can be a beautiful ornamental plant with its large, textured leaves and chunky stems. Rhubarb plants are generally hardy and long-lived, with some varieties growing for 20 years or longer.

I. Appearance and Characteristics 

Rheum rhabarbarum is a species of flowering plant in the family Polygonaceae, native to a region stretching from southern Siberia to north and central China.

Rheum rhabarbarum was first described by Carl Linnaeus in 1753. Linnaeus also described R. undulatum, but this is now considered to be the same species.

The name rha barbarum, Latin for ‘foreign rha’, was first used in the writings of Celsus, who uses the word to describe a valued medicinal root imported from the east.

Rhubarb (Rheum rhabarbarum) is a hardy perennial that will grow from 61 to 122 cm tall. Heart-shape leaves with thick, succulent red or green leaf stalks grow up to 46 cm long. Foliage dies back each winter. Flower stalks with hundreds of small white flowers bloom in summer and are yellow or pinkish green. Fruits with seeds ripen in fall.

In China, it is known as a species growing on mountain slopes at 1,000–1,600 m elevation. In Russia it occurs in sandy ground along field edges, on the steppes, and in the regionally uncommon copses of woodland.

In China, it flowers in June, and has fruit after July.

Most documented insect relationships with this species are muddied by the misapplication of the name R. rhabarbarum to plants of R. × hybridum. As such, most of the insects which are said to use this species as a food plant are generalists from Europe or North America which did not actually eat this species nor are native to the region where this species occurs. An exception is the butterfly Lycaena violacea, whose caterpillars are only known to feed on R. rhabarbarum and whose range is concurrent with that of its host plant (most Lycaena spp. are specialised on Polygonaceae).

Cosmia trapezina var. exigua is roughly native to some of the same areas, and its European variety has been found to have eaten rhubarb in Finland (it usually feeds on various tree species). Other species found to eat (garden) rhubarb which occur in the native range of this plant are Arctia caja, Hydraecia micacea, Spilarctia luteum and Xestia baja.

II. How to Grow and Care

Sunlight

Rhubarb tends to produce best when planted in full sun, meaning at least six hours of direct sunlight on most days. However, plants in the warmer growing zones usually benefit from some afternoon shade, especially during the hottest months of the year. Too much shade, however, can result in thin stems.

Temperature and Humidity

Rhubarb likes climates in which the average temperature is below 40 degrees Fahrenheit in the winter and below 75 degrees Fahrenheit in the summer. It can be grown as an annual in warmer areas; however, too much heat can cause it to have thin stalks and leaves. Dry climates will make it difficult to maintain the level of moisture rhubarb craves, though a layer of mulch to conserve soil moisture can help.

Watering

Rhubarb likes consistent moisture. While mature plants can be somewhat tolerant to drought, rhubarb in its first two years of growing needs regular watering. However, don’t overwater rhubarb, as the crowns can rot in wet soil. A good rule is to water the plant when the top inch of soil dries out.

Soil

Rhubarb prefers a slightly acidic to neutral soil pH. In addition, it likes soil that’s high in organic matter, which helps to support its growth. The soil should be moist but well-draining. If you have heavy soil, such as clay, consider planting your rhubarb in raised garden beds to provide the appropriate growing environment.

Fertilizing

Rhubarb needs lots of organic matter, such as compost, in the soil to grow well. Don’t use any chemical fertilizer on a young rhubarb plant, as the nitrates can kill it. You can add an organic fertilizer around your plant at the start of its second growing season, but make sure it’s safe if you intend to eat your rhubarb.

Pruning

Remove any flower stalks, which are taller than leaf stalks, as soon as they appear. If rhubarb is allowed to mature and flower, the leaf stalks will be thinner.

Propagation

Rhubarb is best propagated by division. You can do this in the early spring or fall, though it’s easier in spring when the plant is coming out of dormancy and growing new roots. Dividing rhubarb plants roughly every five years is ideal to keep them healthy and vigorous. You’ll know it’s time to divide when the plant starts to produce thin stalks. Here’s how:

• Dig up the plant, keeping its roots as intact as possible.
• Gently split the crown into pieces around 2 inches across with roots attached to each section.
• Replant the sections at least 4 feet apart (or in entirely different locations). Water well.

How to Grow From Seed

Rhubarb is not commonly grown from seed, as it can take several years to get a good harvest and sometimes seeds can be difficult to find. If you wish to start plants from seed, fill a tray with moistened seed-starting mix. Soak the seeds in warm water for about an hour before planting, and then plant them about an inch deep. Cover the tray with plastic wrap to retain moisture, and place it in bright, indirect light. Ensure that the soil remains moist but not soggy. Seedlings should appear in one to two weeks. 

Potting and Repotting 

A well-draining potting mix made for vegetables is typically good for rhubarb. Plant the crown around 4 inches deep in the pot just like you would in the ground, and water after planting to evenly moisten the soil.

Plan to repot once you see roots growing out the bottom of the container and up above the soil line. You’ll likely have to do this roughly every three years, depending on your container size. You can either divide the plant into separate containers or repot the whole plant into a larger container. Wait one growing season before harvesting from a repotted rhubarb plant.

Overwintering

Rhubarb stems will die back in the fall. At that time, cut the depreciated foliage to the ground. Then, cover the plants with 2 to 4 inches of mulch once the ground freezes to protect the roots and keep them from drying out over the winter.

Pests and Diseases

Rhubarb can be susceptible to crown rot, especially in poorly drained wet soils. Foliar leaf spots also can occur, but while disfiguring, this does not usually hinder harvest of the stalks.

Moreover, stalk borers, beetles, and rhubarb curculio can infest rhubarb. Either organic or chemical pesticides will generally control these, though you should follow label directions for using these compounds with edible plants. Keep the ground around the plants free of debris to remove breeding areas.

III. Uses and Benefits 

Ornamental uses

The humongous leaves of rhubarb are interesting and ornamental, growing from spring through autumn. This plant is especially showy in the summer when its colorful flowers bloom. While it can be used as an accent or border plant in moist, sunny wildflower garden beds, it’s often grown in vegetable gardens for its culinary value.

Culinary uses

Rhubarb is a versatile ingredient that can be used in various sweet and savory dishes. Some common ways to cook it include:

• Rhubarb pie: It is often paired with sugar and used in pies, tarts, and cobblers. It provides a tart contrast to sweet fillings.
• Rhubarb compote: It can be simmered with sugar and water to create a compote that can be used as a topping for ice cream, yogurt, or pancakes.
• Rhubarb sauce: It can be blended with sugar and spices to create a sauce that can be used as a topping for meats or as a glaze for roasted vegetables.
• Rhubarb crumble: It can be paired with sugar and topped with a crumbly topping made from flour, butter, and sugar to create a delicious dessert.
• Rhubarb jam: It can be cooked with sugar and pectin to create a tangy, spreadable jam that can be used as a topping for toast or as a filling for cakes and pastries.

When cooking with rhubarb, it is important to balance the tart flavor of the stalks with sugar or other sweeteners to create a balanced, enjoyable dish. Additionally, it should always be cooked or processed before consumption, as the raw stalks can be tough and difficult to digest.

Health Benefits 

The stalks of rhubarb are a good source of several essential vitamins and minerals and have been associated with several health benefits. Some of the potential health benefits include:

• Antioxidant properties: Rhubarb is a good source of antioxidants, which help to protect cells from damage caused by free radicals.
• Vitamin K: One serving of rhubarb (100 grams) contains approximately 26% of the recommended daily intake of vitamin K. This vitamin is important for blood clotting and bone health.
• Fiber: Rhubarb is a good source of fiber, which can help to improve digestion and support healthy gut bacteria.
• Vitamin C: Rhubarb is a good source of vitamin C, which is an essential nutrient that helps to support a healthy immune system.
• Calcium: One serving of rhubarb (contains approximately 15% of the recommended daily calcium intake. Calcium is essential for strong bones and teeth.

• Potassium: Rhubarb is a good source of potassium, which helps to regulate blood pressure and support heart health.
• In addition to these essential nutrients, rhubarb also contains smaller amounts of other vitamins and minerals, including vitamin B6, folate, and magnesium.
• Rhubarb is often paired with sugar in cooking, so it is important to enjoy it in moderation as part of a balanced diet.
• Nutrition Facts (per 100 grams): 116 calories, 31.2 grams carbs, 0.4 grams protein, 0.2 grams fat, 2 grams fiber.

IV. Harvesting and Storage

Harvesting

Do not harvest the first year after planting, but in the second year, only harvest a few stalks. In subsequent years, harvest the stalks in the spring and early summer, taking care not to damage the crowns.

Here are some guidelines for harvesting this wonderful plant:

• Timing: It is usually ready to harvest in late spring or early summer, depending on the variety and the climate. The stalks should be at least as thick as a pencil and around 12-18 inches long.
• Method: To harvest, gently grasp the stalk near the base and gently pull it from the plant. Take care not to damage the crown or the surrounding plants.
• Frequency: It is important not to over-harvest rhubarb, as this can weaken the plant and reduce its overall health. In general, only harvest a few stalks at a time, and avoid harvesting the entire plant.
• After-harvest care: After harvesting, water the plant well to help it recover from the loss of the stalks. Additionally, consider removing any yellow or wilted leaves to reduce disease risk.
• By following these guidelines, you can successfully harvest rhubarb and enjoy this delicious and versatile ingredient in various sweet and savory dishes.

Storing

Rhubarb can be stored in various ways to extend its shelf life and stay fresh and flavorful. Here are some tips for storing:

• Fresh storage: If you have just harvested your rhubarb or purchased it from a farmer’s market, store it in the refrigerator in a plastic bag. It will keep in the refrigerator for up to 7 days.
• Freezing: Rhubarb can also be frozen for long-term storage. Wash and chop the stalks, then spread them in a single layer on a baking sheet and freeze until solid. Once frozen, transfer it to a freezer-safe bag or container and store it in the freezer for up to 8 months.