GardenLine | Vegetables | Rhubarb

The leaves of rhubarb contain a high concentration of oxalic acid salts. The salts can be very toxic, so rhubarb leaves should never be consumed by humans or fed to animals. The leaves provide a good source of organic matter in a compost pile. The edible portion of the plant is the leaf stalk (petiole), which contains very low concentrations of oxalates. A high calcium intake should be maintained when rhubarb is being consumed in large quantities.

Soil Preparation

The ideal soil for a rhubarb patch is a clay loam. As with asparagus, the soil should be prepared with large amounts of organic matter. Soil preparation for rhubarb is the same as for asparagus.

Propagation

Named varieties are propagated by division of the crown and root system. The plants to be divided are dug up in early spring, and the clumps are cut into sections so that each section has a portion of the crown and root system. The leaves arise from the crown. Each section should contain at least 2 or 3 buds, with a good section of root. The larger the crown, the more rapidly will the plant become established.

Eventually the clumps become large and the buds become crowded. This results in smaller leaf stalks and indicates that it is time to renew the patch. Though a patch will produce for 15 years or more, optimum yield comes from patches 10 years and younger. Division of the crown and root is best done in early spring just as growth starts.

Planting

The best time to plant rhubarb is in early spring as soon as the frost is out of the ground and before much growth has occurred. Dig a hole sufficiently large to accommodate the root and crown. Spread the roots out evenly and fill the hole in with a soil:peat moss mixture (equal parts by volume). The division should be planted so that the top of the crown is not more than 2.5 cm (1 in.) below the soil surface. Adequate watering is required during the year of establishment. The between-row spacing should be 1.5 to 1.8 m (5 - 6 ft.), with an in-row spacing of 91 to 120 cm (3 to 4 ft).

Cultural Requirements

Rhubarb plants respond well to moisture, although reliable yields can be obtained with minimal watering. Fertilizing is not recommended during the year of planting. Weed control is required to eliminate any competition to the developing crowns. Care should be exercised not to injure the leaves when tilling. In the spring of the second and subsequent years after planting, about 5 cm (2 in.) of well-rotted manure should be tilled into the top 5 cm of soil. Shallow tillage is essential so as to not injure the crown. In the spring an application of commercial fertilizer is also beneficial. No more than 100 to 115 gm (approximately 1/4 cup) of a high-nitrogen fertilizer (e.g., 34-0-0) should be applied in a 90 cm (3 ft) circle, with the plant at the center. Shallow tillage will incorporate the fertilizer.

The plants should not be allowed to produce seed; when the plants devote energy to seed production, the development of leaf stalks is curtailed. Remove flower heads as soon as they appear in the spring.

Pests

Only one disease of importance is found on rhubarb in Western Canada. Red leaf disease of rhubarb commonly attacks the roots and crown areas of the plant. The leaves of the affected plants become reddish and later wilt and shrivel. New leaves cease to appear, and all that remains of the plant above ground is a few dry leaves. In some plants this process is slow, while in others it is rapid. Examination of the parts below the ground reveals decay in varying amounts. With plants showing only reddening of the leaves, the roots may appear normal on the outside, but their centers will be found to have rotted away. Some rotting in the crown will also be evident. In more advanced stages, when the leaves become dry, the greater portion of the root and crown will be found in a decaying condition.

There is still no good measure of control for this disease. The causal agent is not known, and until it has been found, no definite control measures are likely to be formulated. Shallow planting and a generous moisture supply may help to reduce the incidence of this disease. Affected plants should be completely removed as soon as possible after they show signs of this disorder. It is also good practice not to place new plants in soil where diseased plants have grown.

Harvesting

Do not harvest during the year of planting and during the next year. As with asparagus, the root and crown must be allowed to grow in order to store energy reserves. Full harvest can begin the third year after planting. No more than two-thirds of the larger stalks should be removed at any one time.

In harvesting rhubarb, simply pull the stalks; this will usually cause them to separate from the crown. Alternatively, you may cut the stalks at ground level. Harvesting usually begins in late May and continues until July. Under most conditions, harvesting should cease at the end of July to allow the food reserves to build up again in the roots and crown.

Winter Preparation

Watering rhubarb should continue until late fall. Watering requirements are the same as those for asparagus. Mulching to prevent winter injury is generally not required, since the crown is below ground level. A few inches About 5 cm (2 in.) of organic matter can be placed over the row in late fall, then tilled lightly into the soil in early spring. Dead leaves should be removed in early spring.

Varieties

Both red- and green-stalked varieties are available. Although the green varieties are more productive, the red varieties are preferred by most people. Macdonald is probably the most common variety available, but Valentine, Ruby, Canada Red and Sunrise are also acceptable.

Don Dabbs and Grant Wood

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.