Rhubarb Plant Profile

woman holding harvested rhubarb

 Deidre Malfatto/Stocksy

Rhubarb (Rheum rhabarbarum) is a vegetable that’s usually prepared and eaten like a fruit and is 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. Plant in the early spring, but don’t start harvesting until the second growing season. 

Botanical Name Rheum rhabarbarum
Common Name Rhubarb
Plant Size Perennial vegetable
Mature Size 34 feet wide and 23 feet tall
Sun Exposure Full sun
Soil Type Well-drained, fertile, moist
Soil pH 5.56.5
Bloom Time Early summer
Flower Color White
Hardiness Zones 38
Native Area Asia

How to Grow Rhubarb

Rhubarb is usually grown from purchased crowns (root divisions) rather than from seed to have harvests sooner. In early spring once the ground becomes workable, plant your rhubarb crowns around 2 inches deep and 4 feet apart. If placed too closely, the rhubarb will be smaller and less productive. You can plant in a long trench, much like asparagus, or dig individual holes. After planting, water the rhubarb well.

Remove any flower stalks, which are thicker and taller than leaf stalks, as soon as they appear. If allowed to mature and flower, the leaf stalks will be thinner. Moreover, rhubarb does not like competition from weeds. A 2-inch layer of mulch will suppress weeds and help to conserve water.

Rhubarb plants generally have very few pests or diseases. But look out for rot and fungal diseases, such as foot rot, due to soggy soil and poor air circulation. And keep an eye out for black spots on the stems, which might be a type of beetle called rhubarb curculio.

Light

Rhubarb tends to produce best when planted in full sun. However, plants in the warmer growing zones usually benefit from some afternoon shade, especially during the hottest months of the year. Too much shade can result in thin stems.

Soil

Rhubarb prefers a slightly acidic soil pH of around 5.5 to 6.5. 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.

Water

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

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 can help. Moreover, place a thick layer of mulch over your rhubarb once the ground freezes. This will help protect the roots from drying out while the plant is dormant.

Fertilizer

Rhubarb needs lots of organic matter, such as compost, in the soil to grow well. Don’t add any chemical fertilizer to 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. 

Propagating Rhubarb

Rhubarb should be trimmed and divided around every three to five years. You'll know it's time when the plant starts to produce thin stalks. To divide rhubarb for propagation, dig the root mass and split the crown into pieces around 2 inches across with the roots attached. Then, replant the healthy sections a few feet apart (or in another location entirely). 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.

Varieties of Rhubarb

There are several types of rhubarb, each with certain attributes that make it desirable to grow. Here are a few common varieties:

  • Victoria: This is a popular rhubarb variety for cooking, thanks to its mild and tender stalks.
  • Valentine: This variety is hardy against climate fluctuations and diseases.
  • Crimson Cherry: This variety is known for its sweetness.
  • Canada Red: This plant does well in colder climates and contains more sugar than many other rhubarb varieties.

Toxicity of Rhubarb

Only the stalks of rhubarb are edible. The leaves are poisonous and should be removed at harvesting. They contain oxalic acid crystals, which are toxic to both humans and animals. Moreover, frost damage can cause the oxalic acid crystals to move into the rhubarb stalks. So if the stalks are not firm and upright, do not eat them.

Some symptoms of poisoning include weakness, difficulty breathing, burning or pain in the mouth and throat, stomach pain, nausea, vomiting, diarrhea, and tremors. The symptoms are similar in both humans and animals, and they should be addressed by a medical professional as soon as possible.

Harvesting

Don't harvest any rhubarb in your plant's first growing season to allow it to become established. You can take a small harvest in the second growing season. During the third season, you can harvest rhubarb for around one month. And after the third year, you can harvest whenever there are stalks ready for picking. However, if you're growing rhubarb in a warm climate as an annual, you can harvest all you want the first year because the plant likely won't survive a second year.

The main harvest season is the spring, though smaller harvests might continue throughout the summer. To harvest, cut the stalks at the soil line, or pull out individual stalks as needed. You can harvest the whole crop at the same time or over a four- to six-week period.