Rhubarb (Rheum rhabarbarum) is an herbaceous edible perennial and a member of the buckwheat family.
It is native to Siberia and has been used as a medicinal plant in Asia for over 5,000 years. It was once a very well-known and popular vegetable in the U.S., introduced by European settlers in the 1700s.
It is commonly known as the “pie plant,” grown for its edible, very tart leaf stalks (petioles), which can reach 12 to 18 inches long and one to two inches thick, with a crispy texture similar to a large celery stalk. The leaves are toxic because of their oxalic acid (soluble oxalates) content, which can cause human and animal poisoning and must be trimmed from the petiole prior to use.
Rhubarb is successfully grown as a cool weather perennial by planting crown divisions, which can be cut into sections that contain a piece of the rhizome and a bud that is planted about one inch deep in the soil. Rhubarb requires at least 500 hours of winter temperatures from 28 – 49º F (chilling hours) for plants to go into a rest period and adequately form new leaf buds. When summer temperatures exceed 75º, plants become stressed and more susceptible to root-rotting soil fungi and bacteria, causing rapid decline and plant death. This severely limits its growth as a perennial, causing it to be poorly adapted to the southern half of the U.S.
Researchers discovered that if rhubarb was seeded in August in Florida and set out in the field as 10-week-old transplants, with a harvest between late January and late April (without undergoing a period of rest), yields were always higher than crown division-propagated rhubarb, even though the seed-propagated rhubarb had variable plant vigor and petiole shape and color.
I hypothesized that if growing rhubarb as an annual crop was successful in Florida, it should be successful in North Carolina, with the added benefit of plants having the ability to go into rest to store nutrients in the crown of the plant to prevent nutrient depletion and enhance their survivability before harvesting them the following spring. People who move south from northern states and are familiar with rhubarb will buy it if it is available to them.
Based on the researchers’ success with the “Victoria” cultivar, Victoria rhubarb was seeded at Aarons Creek Greenhouses in Buffalo Junction, VA, in 2011, on May 2, 16 and 30 and June 13 to correspond to 10-week field transplanting dates of July 15 and 28 and Aug. 11 and 25, respectively. It was hypothesized that because the rhubarb will go into rest during the winter months, the more plant growth that was made before rest, the higher the petiole yield would be the following spring. It was also hypothesized that even though July and August transplanting dates would be above 75º, it would allow for plant growth to continue at cooler temperatures in autumn before plants went into rest.
A completely randomized block design with 10 plants/plot and four treatments (planting dates) with six replications was used, for a total of 60 plants/planting date for a total of 24 plots. Each plot consisted of plants spaced two feet between plants in the row and five feet between rows to equal a plot row length of 20 feet. The study was done 12 miles north of Oxford, NC, in a Cecil clay loam soil.
Soil samples were taken and fertilizer and limestone were added according to the soil test recommendations. Plants were hand-watered as needed to keep soil moist down to a six-inch depth. Plots were hand-weeded since there were no labeled pre-emergence herbicides for rhubarb. Emerged grassy weeds were controlled with Poast herbicide. Minor damage done by the rhubarb curculio was noticed and Cercospora leaf spot was observed on some plants, but it was minor as well.
The plants underwent a rest period after autumn frosts and freezing temperatures were encountered. In the spring of 2012, the crowns initiated new buds where new leaves and petioles emerged from dormant crowns.
No freezing events occurred during the spring of 2012 and five harvests were taken: April 13 and 27, May 12 and June 6 and 27. After the last harvest, plant health began to decline, with leaf browning and crowns becoming decayed.
Leaves and petioles were harvested after they reached a length of at least eight – 10 inches. Petioles were gently pulled up and away from the plants and were not cut, which is the accepted harvesting method. After harvesting, a small amount of leaf was left attached to the petiole so that the tips of the petioles did not dry out in cold storage. Petioles were weighed after most of the leaf was removed.
Yield data was recorded in pounds/acre. This was obtained by dividing the total square feet of one plot row (100) into 43,560 (the number of square feet in one acre) to get approximately 435 100-square-foot rows in one acre. Data recorded were total yield per acre for each transplanting date.
The July 15 transplanting date had the highest yield, followed by the Aug. 11, July 28 and Aug. 25 dates, respectively. However, the yield differences between transplanting dates were not statistically significant.
On a per acre basis, rhubarb seed cost is $240. Labor costs per acre were estimated at 35 hours for production, 192 hours for harvest and 13 hours for packing. Greenhouse costs of growing the 10-week-old transplants need to be calculated as well.
If a grower harvested 3,000 pounds/acre, a retail price of $2/pound could bring the grower $6,000/acre, making rhubarb a high value and profitable horticultural crop when grown as an annual plant.