Pie is usually what comes to mind first when people see rhubarb. The tart, stalk vegetable has a wide variety of uses including in jams, jellies and medicinal treatments as long as the leaves, which contain oxalic acid and are toxic, are not eaten. According to Dalhousie University in Nova Scotia, Canada, rhubarb is commonly used in traditional Chinese medicine for treating an assortment of diseases and illnesses from bacterial infections to urinary tract lesions, constipation and cholesterol.
In the United States, it’s considered a specialty crop with limited commercial acreage in production, yet it is still in high demand.
“There is not a code in the U.S. Department of Agriculture’s Economic Research Service for the crop so estimates are interpolated from the reported statistics in Oregon,” said Shawn Wright, horticulture specialist at University of Kentucky’s Robinson Center. “It was once a staple in home gardens and since those are less common than 75 years ago, rhubarb isn’t as common as it once was,” he said.
The cool-season perennial plant is a winter hardy plant that prefers moderate summer temperatures and winter temperatures that dip to 40 degrees and below, which allow the plant to go dormant. Thus the plant performs best in northern climates such as the Pacific Northwest and New England.
Kentucky, Wright’s home state, is the lower latitude for production of rhubarb because it gets too hot in the summer and not cold enough in the winter.
“Temperatures above 90 degrees limit growth in the summer,” he said. “In the United States it does best across the Northern Tier states.”
For growers in the right climate, there is a lot of opportunity for the spring-ready crop. Nourse Farms, the Whately, Massachusetts nursery that produces certified plant material for growers and home gardeners, sells out of stock by early February each year (see the profile on page 11).
In this article, you can find tips for planting, maintaining, harvesting and selling an economically feasible rhubarb crop.
Rhubarb was once considered a hardy, relatively easy crop to grow, but borne diseases have made it increasingly difficult to produce. Cultural practices play an important role in establishing and maintaining a healthy crop.
Before planting, conduct a soil test and adjust soil pH levels so that they are between 5.6 and 6.8. Wright recommends a soil pH of 5.6. Choose a field with deep, loam soils that are well-drained to limit the occurrence of Phytophthora root rot, a soil-borne disease that can ruin rhubarb crops.
The “2017 Midwest Vegetable Production Guide For Commercial Growers,” produced by a collaborative, multi-state effort, offers fertilizer recommendations for establishing a new crop and for annual maintenance. According to the guide, apply 50 pounds of nitrogen per acre, up to 150 pounds of phosphate and up to 200 pounds of potassium preplanting. Make adjustments according to soil type, previous management and soil test results for your state. An additional 25 pounds of phosphate can be applied directly in the furrows when setting the rootstalks (divided crowns).
Wright pointed out that the crop prefers soils with a relatively high percentage of organic matter. Some experts recommend adding up to 15 tons of compost prior to planting.
While plants can be grown from seed, using divided crowns creates a more uniform stand. Commercially available crown size can vary from one to three shoots per crown. Buy from a reputable supplier for disease-free crowns. Wright explained that the divisions will have buds similar to a potato cutting. In-row plant spacing is generally 3 feet between plants and 5 to 6 feet between rows.
After the first year, only nitrogen is needed at a rate of 50 pounds per acre before the beds are worked in the spring. After new growth resumes, top dress with 35 pounds of nitrogen per acre.
Even though rhubarb is a perennial plant, Wright and others have investigated growing rhubarb as an annual in warmer climates like Kentucky.
“We get cold enough in the winter, and by growing it as an annual we can avoid the problems associated with high summer temperatures and humidity,” he said. “We are still trying to determine optimum seeding date, planting date, and other production practices.”
In this scenario, Wright is using seeds to produce plugs for use in an annual production model.
“If – this is a big if for folks here – it grows well, the plants will need to be divided every four to six years to prevent the plant from becoming overcrowded and producing thin, spindly stalks,” Wright said.
Green rhubarb yields range an average of 10 – 18 tons per acre and red varieties yield approximately half that amount. Consumers prefer the red color, but a blind taste test might reveal no significant difference.
“I can’t tell any difference in taste,” Wright said. “I did a variety trial with commercial varieties and things only available from the USDA’s Germplasm Resources Information Network and found that in my study, the quality of the crown pieces was more important than varieties in terms of survival.”
In Nourse Farms field trials, the greener the strain, the easier it is to grow and it is less susceptible to soil-borne disease. One popular variety is MacDonald, a green variety, and though its color is not as popular, it is more vigorous and a consistent producer. Cawood Delight is another variety used at Nourse Farms and one that is a red-color requirement. The plant is compact with very thick stems. Sutton and Valentine are two additional varieties that are referenced in the “2017 Midwest Vegetable Production Guide For Commercial Growers.”
Ultimately, flavor isn’t as much of an issue as tenderness. “I would encourage people (to) get a couple of crowns of several varieties to diversify their risk,” Wright said.
Pests, diseases and weeds
Rhubarb curculio is the most common pest and it bores into the stem. Sanitation is key for managing the pest. Dock weeds (like curly dock Rumex crispus) are an alternate host for the curculio and can be used to lure the pest away from rhubarb. Wright added that tarnished plant bug, aphids, slugs, flea beetles and potato stem borer are other pests that can occasionally attack rhubarb plants.
Tank mixing insecticides with fungicides beginning in the early spring and lasting throughout the growing season can be helpful in managing pests and reducing the prevalence of Phytophthora root rot.
Check with your local cooperative Extension agent for recommendations on products that are approved for use in your state. For example, in Kentucky, Wright said he was unable to find any products labeled for use on rhubarb. However, the “2017 Midwest Vegetable Production Guide For Commercial Growers” offers suggestions for products available for use in Midwestern states.
“Wildlife isn’t a problem, as they don’t like rhubarb,” Wright said. “There will be someone who thinks it is; there is always that one person who has issues. This year I am fighting coons clipping off my summer squash plants and that is a first for me.”
The most significant issue for rhubarb is crown rot so it’s important to avoid wet soils.
“Leaf spots can be an issue, so water the soil, not the plant,” Wright said. “Promote good airflow through the planting by removing weeds and not overplanting or allowing plants to become too thick (divide the plants every few years if they are getting too thick).”
Shallow cultivation and approved herbicides can easily control weeds. As mentioned earlier, rhubarb likes organic matter so an application of organic mulch can benefit the plant and potentially smother weeds.
“Some people will use landscape fabric with holes cut for the crowns but this can potentially promote crown rot,” Wright said.
Patience is key with rhubarb. Once planted, do not harvest in the first year. In Nourse Farms’ spring newsletter they recommend allowing rhubarb to establish for three years prior to harvest, developing 2-foot diameter crowns. Two years after planting, harvest lightly depending on the amount of growth in your field.
Harvesting too much is another common mistake. Leave a minimum of 25 percent to 30 percent for healthy regrowth or leave two to three stalks and up to 30 percent to 50 percent in the field. Another rule of thumb is to end harvest when new stalks emerge thin or spindly.
When harvesting, pull leaf stalks near the base and don’t cut. Remove no more than one-third of the stalks. Harvest period can be 4 – 8 weeks depending on where you are and plant health. Because it is a perennial you need to leave some leaves to nourish the crown for the next year’s production.
Harvesting too late in the season will result in tougher and mealy stalks.
It can be a profitable crop for farmers markets if you can get good production. The crop has comparatively few pest problems and it is perennial so you don’t have to replant every year. Since commercial production is limited, you can corner the market locally.
Because of the limited availability of locally grown rhubarb, it brings a healthy price at market. As with any crop, knowing your costs of production is important to develop and sell an economically feasible crop.
Wright also suggested having more than one marketing stream or outlet for the rhubarb you raise. For example, the local farmers markets, high-end restaurants and a roadside stand may be needed to market and sell the crop.
Since most people think of rhubarb strictly in terms of pie, it’s helpful to give them ideas of other ways to use the vegetable.
“Let people know that they can do more than make strawberry-rhubarb pie with the vegetable,” Wright said. “Have recipe cards available to help educate the consumer about all they can do with it.”
True success boils down to quality. “Sell good-quality stems,” Wright said. “Too often, I see people taking less-than-ideal produce to the markets thinking ‘something is better than nothing’ but that isn’t the case.”