Rheum

( REE - um )

At-A-Glance Information

Commonly known as Rhubarb, this flowering perennial plant needs either full sun or partial shade and ample water. Plants are grown for their beautiful foliage and their flower bracts which form clusters of color in spring and summer. Flowers are typically greenish white to rose-red. Most species are native to eastern Europe, southern and eastern temperate areas of Asia, and to a lesser extent tropical Asia. Species are cultivated worldwide as crop plants. Take care when planting some species of this genus in the garden, as fresh leaves are toxic if ingested.

Rheum Species and Varietals

The genus Rheum includes around 60 ornamental and crop species and is a member of the plant family Polygoniaceae. Most species and varietals of Ornamental Rhubarb grow best in zones 2b-7 and 14-17. To find your zone, click here: Zone Map.

Rheum australe (Rheum emodi) (Himalayan Rhubarb, Indian Rhubarb, Red-Veined Pie Plant)
Native to the Himalayas, this plant reaches 4-10 feet tall and 6-8 feet wide, with red-veined leaves. Flower plumes are white, yellow, or dark reddish-purple and stretch to 8-12 inches in length. This is known as a medicinal plant, but the species is not commonly cultivated as a crop.

Rhubarb x hybridum (Cultivated Rhubarb)
This group of hybrids and cultivars are known as garden crops, and mostly hail from central Asia. There are many different varieties, listed below:

'Hawke's Champagne'

'Grandad's Favourite'

'Stein's Champagne'

'Timperley Early'

'Reed's Early Superb'

'Victoria'

'Early Albert'

'Glaskin's Perpetual'

'Valentine'

'Crimson Cherry'

'Canada Red'

Rheum maximowiczii
Native to mountainous regions in central Asia, these plants produce round leaves with wavy margins. Each plant produces a single, unbranched reddish leafless stem to 40 inches tall that holds greenish-yellow flowers with long stamens from May to June in the plant's native range.

Rheum nobile (Sikkim Rhubarb, Noble Rhubarb)
These giant herbaceous plants are native to the Himalayas, and reach up to six and a half feet tall when in bloom. Plants form a conical tower of delicate, shiny straw-colored to whitish leaves; ones higher up on the plant have pink edges. Lower leaves are green. Sikkim Rhubarbs bloom annually in June and July in their native range.

Rheum officinale (Chinese Rhubarb, Indian Rhubarb)
These plants are native to China, and typically reach up to 6.5 feet tall when mature and in bloom. The roots of these plants are used in traditional Chinese medicine practices. Leaves are green.

Rheum palaestinum (Desert Rhubarb)
These plants are native to Israel and Jordan, and produce broad, rigid leaves with a waxy surface. Basal foliage is green, and plants produce multiple branched flowering stems. This species prefers to grow in rocky substrate.

Rheum palmatum (Chinese Rhubarb, Ornamental Rhubarb, Turkey Rhubarb, East Indian Rhubarb)
This plant reaches 6-8 feet tall and 6 feet wide and is native to China and Tibet. Leaves are deeply cut and toothed, and flowers are red, borne on plumes reaching 2 feet in length. Variety 'Atrosanguineum' is tinted red, and Rheum palmatum tanguticum (pictured) is tinted purple, with flowers in white, pink or red.

Rheum rhaponticum (False Rhubarb, Rhapontic Rhubarb, Rhapontic)
This species is thought to be an ancestor of modern culinary Rhubarb hybrids, and is native to Europe. These robust plants grow from woody rhizome roots, and produce heart-shaped basal foliage with prominent veins. Flowers are light greenish white to yellow in color.

Rheum ribes (Syrian Rhubarb, Currant-Fruited Rhubarb, Warty-Leaved Rhubarb)
These plants are native to temperate and subtropical regions in the Middle East and India. These stout perennials produce a plant up to 3 feet tall with reddish-green foliage. Flowers are small and white to cream-yellow.

Caring for Rheum

Plant Rheum, or Rhubarb, in early springtime once the last threat of frost has passed by. Rhubarb is typically purchased as crowns (root divisions) rather than from seed, as this speeds up the harvesting time by quite a bit. Crowns should be spaced about 4 to 6 feet apart for best results, and buried 4 inches deep under the soil surface. If Rheum plants are spaced too closely, they will not produce well. Choose a space in the garden that receives full sun; ideally they appreciate between 6 and 8 hours of direct sun each day to produce (or flower) well. In warmer climates, they do like to get some afternoon shade during the warmest hours of the day (typically between 2 and 3 PM). Too much shade, however, can result in thin stems. Ensure that soil is well-draining and fertile, amended with plenty of organic material. They like a soil pH in the range of 6.0 and 6.8 (slightly acidic). If local soils are particularly poor in nutrients, are heavy clay, or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Rhubarb also does very well in raised garden beds. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention.

Water newly planted Rhubarb plants regularly to help them develop strong root systems. At maturity, these plants are somewhat drought-tolerant, though they will produce and flower better if provided with consistently moist soil. Take care not to overwater Rhubarb plants, as doing so can lead to the crowns rotting out. As a general rule of thumb, water whenever the top inch or two of soil feels dry to the touch. Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. These plants are not heavy feeders, and this should be sufficient to provide the necessary nutrients for the active growing and flowering seasons.

Harvesting Rhubarb
When grown as perennials, Rhubarb plants are typically harvested only after the second year in the ground; if harvested earlier, plants have a much tougher time getting established. The second year, a small harvest can be taken, and in the third season, a full harvest can be taken. As a general rule of thumb, never harvest more than 1/3 of the foliage on any one plant. Grown as annuals, plants can be harvested in their first year, as they will be pulled out at the end of the growing season anyway. The best time of the year to harvest Rheum plants is in springtime through early summer. Stalks that are between 12 and 18 inches long and have their full color are perfect for harvesting; using clean, sharp shears, remove the stalks back to the soil line. After harvest is complete, bring the leaves inside to process them.

Do not eat uncooked Rhubarb leaves or stalks, as they are toxic. To process Rhubarb, remove all leafy parts from the stems. Stalks can be cooked immediately, or kept in the refrigerator for up to 1 week. Rhubarb has a tart, sour taste that is often compared to lemons or sour green apples. It is typically cooked with sugar or paired with sweet fruits to help balance the sourness. The cooked flavor is described as pleasantly tart with a hint of celery. Use Rhubarb in baked goods like pies and cakes, turn it into a preserve like jam or jelly, or use it to flavor ice cream.

Propagation

Rheum, or Rhubarb, can be propagated by division or seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the division method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant, especially if you are propagating a hybrid cultivar. To propagate your Rhubarb plant, follow the instructions below:

Propagating Rheum by Seed

Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
Harvest your seeds. The seed heads on plants are pretty easy to spot, they're left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will continue to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
Get your container prepared. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 2-6 weeks from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 65 and 72 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.

Propagating Rheum by Division
This type of propagation is relatively simple; you will need a clean shovel, mulch, fresh soil (any kind will do, though it does need to be well-draining), compost and pots (only necessary if you will be saving divided plants for transporting elsewhere). Division is best done in very early spring (after the plant has entered dormancy, but before it has begun its new spring growth), and needs to be done every few years regardless of whether you have the goal of propagating the plants for best performance. To propagate by division, follow these steps:

Using a shovel, dig up your existing plant. Start from the outside and work your way in to avoid damaging the root(s). Once you have worked it up out of the ground, lay it out.
Start to tease apart the roots with your gloved fingers. Once the roots are untangled, separate your plant into segments, ensuring that each one has at least one thick root section attached.
Prepare your pot(s) or new planting site(s) with amended, well-draining soil. You can either bring in new soil or simply amend your existing soil with compost to complete this task. Then, plant your divisions and water thoroughly.
Apply a thick layer of mulch over the new planting to protect it from cold weather as it acclimates to its new home. Then, enjoy watching it sprout in the next growing season.