How to Grow Rhubarb

Climate comes first

Rhubarb is a hardy perennial in the buckwheat family, and its needs are set by temperature. Oregon State University Extension says the crown needs at least 500 hours between 28°F and 40°F each winter to form new leaf buds, spring temperatures above 40°F to start growing, and summers averaging under 75°F for strong leaf growth. That profile fits the northern states, the Pacific Northwest and the mountain West. Red Butte Garden lists rhubarb as hardy in zones 3 to 8, while Ohio State says common varieties do well in zones 4 to 7.

South of that band, results drop off. University of Arkansas Extension says rhubarb does not grow well in all parts of the state and recommends cool, north-facing slopes and partial shade there. Texas A&M’s Aggie Horticulture says it does not grow well as a perennial anywhere in Texas, except for an unnamed green variety that does well in the Panhandle north of Amarillo. In hot, dry parts of the West such as Oregon’s high desert, Oregon State recommends late-afternoon shade.

Choosing a site

Because one planting can produce for 10 to 15 years (Utah State), put it at the edge of the vegetable garden or in a sunny flower border where it won’t be tilled. Plants reach about 3 feet tall and wide. Ohio State notes that a south-facing site gives the earliest stalks in Ohio.

Drainage matters more than anything else about the soil, because wet ground invites crown and root rot. Arkansas and Wisconsin both recommend raised beds to keep crowns out of standing water. Oregon State gives an ideal pH of 6.0 to 6.8. Before planting, clear out perennial weeds completely, because you cannot dig around the crowns later. Utah State suggests working 2 to 4 inches of compost into the top 6 inches; Ohio State recommends loosening the soil 10 inches deep and adding 3 to 4 inches of compost or composted manure.

Planting crowns

Buy crowns or divisions rather than seed. Arkansas notes that seedlings are slow to establish and don’t come true to color and size, and Oregon State adds that rhubarb is cross-pollinated, so seedlings seldom resemble the parent. To keep crown rot out of a new bed, Ohio State advises planting purchased crowns rather than seed from a neighbor’s plants.

Plant in early spring while the crowns are dormant or just starting to push buds; Wisconsin times divisions about 4 to 6 weeks before the average last frost. Ohio State also allows fall planting after the plants go dormant, but Oregon State recommends spring wherever winters are severe so roots can build reserves first.

Depth advice varies by an inch or so. Utah State says to keep the bud no more than 1 inch below the surface, Ohio State and Oregon State say 1 to 2 inches, and Arkansas and Wisconsin say 2 inches. All agree that planting too deep delays production, and Utah State warns it can kill the plant. Space crowns 3 to 4 feet apart, with rows 3 to 4 feet apart, firm the soil, and water well.

Feeding, watering and mulch

Don’t fertilize in the first year. After that, feed in early spring as growth begins: Utah State suggests ½ cup of 16-16-16 around each plant, and Oregon State suggests ¾ to 1 cup of 10-10-10 or ½ to ¾ cup of 16-16-16 plus a layer of compost. Ohio State and Wisconsin both recommend a second nitrogen feeding after harvest, since picking draws down soil nutrients.

For the first two to three years, Utah State recommends watering once or twice a week so moisture reaches 6 to 12 inches down. Established plants can go every one to two weeks if the water soaks 12 to 18 inches deep. Oregon State advises letting the top 2 inches dry between waterings and notes that limp leaves mean the plant needs water.

Mulch with straw or compost to hold moisture and smother weeds, keeping it under the leaves and off the crown itself (Oregon State). In cold-winter areas, Ohio State and Wisconsin suggest a few inches of straw once the ground has frozen to reduce heaving and crown rot; pull it back off the crowns before spring growth begins.

Flower stalks and dividing

Cut off seed stalks as soon as they appear. Oregon State lists age, heat, drought, low fertility, swings between hot and cold, and long nights as triggers. Some varieties bolt more than others, and sources disagree on one of them: Oregon State and Wisconsin describe ‘Valentine’ as producing few seed stalks, while Ohio State lists it as more likely to bolt. Both Oregon State and Utah State note that ‘Victoria’ bolts readily.

Divide when stalks get thin and crowded: Utah State says every 5 to 10 years, Ohio State when crowns are 6 to 10 years old, and Oregon State often around the fifth or sixth year. In early spring, dig the crown and split it into pieces that each have at least one strong bud and a good piece of root. Replant right away.

Varieties

Ohio State recommends MacDonald, Crimson Red, Victoria, Canada Red, Cawood Delight, Glaskin’s Perpetual and Valentine for zones 4 to 7. Oregon State names Crimson as the leading outdoor variety in Oregon. Utah State’s Utah list adds Cherry Wine, Early Sunshine and Strawberry. Arkansas recommends MacDonald, noting resistance to root rot, along with Tilden and Victoria. Ornamental Chinese rhubarb (Rheum palmatum) is not edible.

Pests and diseases

• Crown and root rot (Phytophthora): plants fail to leaf out or collapse suddenly. Ohio State says fungicides don’t cure it; prevent it with good drainage, raised beds and healthy purchased crowns.
• Rhubarb curculio: a rusty snout beetle about ¾ inch long that bores into stalks. Remove nearby curly dock, its alternate host.
• Red leaf: Oregon State names this bacterial disease, with Phytophthora, as the most serious problem west of the Cascades. Remove infected plants.
• Slugs: a problem on new plantings and in moist areas.
• Ascochyta leaf spot: clear away old leaf litter and last season’s dead tissue.

Leaves are toxic

Only the stalks are food. The leaf blades contain high levels of oxalic acid, which Utah State says can cause serious illness and kidney failure; the stalks contain very little. NC State’s plant database lists abdominal cramps, burning in the mouth and throat, nausea and vomiting as symptoms, notes that serious poisoning takes large quantities, and lists rhubarb as a problem for dogs, cats and horses. The leaves are safe to compost: Ohio State says the oxalic acid breaks down quickly in the pile.

Growing rhubarb as a winter annual in Texas

Texas A&M AgriLife’s Travis County office describes growing rhubarb as a winter annual around Austin. Sow seed indoors in mid to late August (‘Victoria’ is easiest to find as seed), set plants out in late September or early October when they have three to five leaves, shade them through any lingering heat, and harvest from about March through May before removing the plants. Expect mostly green stalks, partly because of the warm climate and partly because the reddest varieties aren’t sold as seed.