Rhubarb (Rheum rhabarbarum L.) is a cool season, hardy, perennial vegetable, grown for leafstalks that have a unique tangy taste used for pies and sauces. Rhubarb was first cultivated in the Far East more than 2,000 years ago. It was initially grown for medicinal purposes, but was grown for culinary use in Britain and America in the 18th century. Ohio is well-suited for growing rhubarb. This crop requires winter temperatures below 40° F to break dormancy and stimulate spring growth and also needs summer temperatures averaging less than 75° F for vigorous vegetative growth. The tops are usually killed in the first heavy freeze in the fall, but the roots survive and produce new tops the following spring. While the leafstalks are edible, the leaves themselves contain oxalic acid and should not be eaten.
Rhubarb is generally purchased as crowns or divisions, rather than propagated from seed. Purchase rhubarb crowns from a local nursery, garden center, or from seed catalogs. Common varieties that grow and produce well in USDA hardiness zones 4–7 include MacDonald, Crimson Red, Victoria, Canada Red, Cawood Delight, Glaskin’s Perpetual, and Valentine. Rhubarb varieties vary in color and the number of seed stalks produced. Some varieties, such as Valentine, are more likely to bolt than others. Chinese rhubarb (Rheum palmatum), also known as ornamental rhubarb, is not edible.
Rhubarb will grow and produce in most soils, but grows best in fertile, loamy, well-drained soil that has good organic matter content. Careful soil preparation will help rhubarb stay healthy and productive for many years. The planting area should be cleared of any weeds, especially tough, hard-to-control perennial weeds. Other considerations for a planting site for rhubarb include exposure and location. Earliness is favored by a southern exposure, free from shading trees or buildings. Since rhubarb is a perennial, it should be planted to one side or at the end of the garden so as not to interfere with planting and growing annual vegetables. The rhubarb plant has bold ornamental texture and size, and some gardeners find it suitable to include in a perennial flower border.
Planting and Care
Plant the crowns as soon as possible so they don’t dry out. Don’t use crowns that look diseased or stressed. Rhubarb crowns are best planted in early spring when the roots are still dormant, or the plants are just beginning to leaf out. Rhubarb can also be planted in the fall after dormancy has set in. Individual crowns should be spaced 3 feet apart. Loosen the soil to a depth of 10 inches and add fertilizer based on the recommendations below. Cover the crowns with no more than an inch or two of soil. Planting rhubarb crowns too deep will delay production. Press the soil firmly around the roots and water well. As soil and air temperatures begin to warm, new buds will push up through the soil. Once the plants are up and growing, the addition of a 3–4-inch layer of clean straw, compost, or similar mulching material will help control weeds and conserve soil moisture for plant growth and development. Flower stalks should be removed as they appear—they deplete reserves from the crown that supports vegetative growth. Rhubarb, like most vegetables, requires regular irrigation during dry weather. Keep the soil moist but not soggy.
When a rhubarb crown is 6–10 years old, it may be dug up and divided. This should be done as early in the spring as possible. Insert a shovel about 6 inches into the ground next to the base of the plant and lift out the entire crown. Some roots will break off and be left in the ground. Using your hands, a hatchet, or machete, break the crown into fist-sized pieces, each with at least one bud and a large root piece. Pull away the dark brown sheaths left from last year’s stalks. Small pieces with broken roots that are at least the size of a small cigar can be put together and treated as a single crown, but should be given more time to develop before harvesting. Replant the crown divisions as soon as possible. If planting is delayed due to weather conditions, store them in the refrigerator. Rehydrate the divisions before planting by soaking them in water for at least two hours, or preferably, overnight.
Work the following nutrients into the soil prior to planting crowns and adjust the values based on a soil test report for the site and the site’s planting area characteristics.
- Nitrogen (N): 1¼ pounds N per 1,000 square feet
- Phosphoric acid (P2O5): 0-3¼ pounds per 1,000 square feet
- Potash/Potassium oxide (K2O): 4½ pounds K2O per 1,000 square feet
If no soil test is available, work 2–3 teaspoons of a complete fertilizer with a 1:1:1 ratio, such as 12-12-12 or 13-13-13, into each square foot of soil. Improve the soil’s organic matter by mixing in 3–4 inches of compost or composted manure. Additional P may need to be added when planting crowns.
To maintain established rhubarb plants yearly, only fertilize with N. Apply N applications in the spring and again when active growth occurs. Side-dress two pounds of N and 2–3 inches of compost per 1000 square feet of soil. Repeat after harvest as nutrients in the soil may be depleted. Do not work fertilizer into soil for established plants.
Pests are usually not a problem on rhubarb in the home garden. However, the rhubarb curculio, a rusty snout beetle about 3/4 inch long, can, on occasion, cause serious damage to the leafstalks. Curly dock is an alternate host for this insect, so dock plants nearby should be removed. Treat the base of curculio-infested rhubarb plants with a pesticide recommended by your Ohio State University Extension county office.
Several diseases are known to cause problems in backyard rhubarb. Crown rot, caused by Phytophthora spp., (a funguslike water mold) is a disease that can be a problem in commercial production, but it is seldom seen in the home garden. Symptoms include plants that fail to leaf out in the spring, or they may leaf out only to die abruptly. Upon digging the plants up, the roots and crowns are rotted. Fungicides have not been found to be effective in eliminating the problem. The best control is prevention. Only plant purchased rhubarb crowns rather than getting seeds from a neighbor, and plant in well-drained soil.
Ascochyta leaf spot may also infect rhubarb. Practice good sanitation by removing leaf litter surrounding plants to remove inoculum. Reduce disease potential by removing dead or dying tissue from the previous growing season.
Harvest and Storage
In order for the plant to become well established, leafstalks should not be harvested the first year and only a few should be harvested the second year. From the third year on, rhubarb is harvested in late April and throughout June in Ohio. Stop harvesting leafstalks when the plant begins to produce slender stalks, a sign that its reserves are low. Never harvest more than one-third to one-half of the plant’s stalks to preserve enough foliage to sustain the crown. The stalks are most flavorful when fairly young, so harvest them soon after the leaf expands. Harvest by grasping each leafstalk near the base and pulling it slightly to one side. Cutting rhubarb with a knife is often debated since the resulting wound may become an entry point for crown rot.
Fresh rhubarb can be stored for two to four weeks at normal refrigerator temperatures and 95–100% relative humidity. Store in perforated polyethylene bags in the refrigerator crisper drawer for best results. After the last harvest in early July, the plants should be allowed to grow until killed by frost. After the tops are dead and the ground is frozen, the plants can be covered with 2–3 inches of straw mulch to reduce the risk of crown rot. Remove mulch from the crown before growth starts in the spring, but leave the remaining mulch around the plants to control weeds.
Rhubarb leaves may be added to your compost pile. While the leaves contain oxalic acid, this rapidly decomposes in the compost pile and has no negative effect on the quality of the compost.
If rhubarb is hit by a hard frost or freeze in late spring, it still can be eaten if the stalks are firm and upright. Leaf injury appears as a brown or black discoloration along the margins of the leaf. If the stems are soft and mushy, don’t eat them. Severe cold injury may cause the oxalic acid crystals in the leaves to move into the stalks, increasing the chance of poisoning. If in doubt about the safety of eating the stalks, don’t. Cut the damaged stalks off and compost them. Allow new stalks to develop for eating.
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