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Growing Rhubarb

Posted - Mar. 6, 2004 at 7:30 a.m.



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Larry A. Sagers Regional Horticulturist Utah State University Extension Thanksgiving Point Office

Perennial vegetables are not common, but two, asparagus and rhubarb, can be planted right now.

Rhubarb can be planted right now as it is a cool season, perennial crop. It requires temperatures below 40 F to break dormancy and to stimulate vegetative growth. Because rhubarb is rarely grown where the summer mean temperature is above 75 F or where the winter mean is above 40 F, the Northern Utah is well suited for rhubarb production. Once planted, rhubarb plantings remain productive for 8 to 15 years.

Give these plants plenty of room as they spread three feet or more. The edible portion of the rhubarb plant is the leaf stalks (petioles). The leaves contain oxalates, that are poisonous to humans if eaten so do not use them as an ornamental next to play areas.

Rhubarb=s unique taste makes it a favorite in pies and desserts. Rhubarb is low in calories, and is a good source of both vitamin C and calcium.

Grow your rhubarb on fertile, well drained soils that are high in organic matter. It responds well to fertilizers the quality of the crop harvested depends largely on the care and fertilization received.

Mulches are a valuable source of organic matter; they help to conserve moisture, preserve the soil structure, and makes nutrients readily available.

Weedy areas make short work of rhubarb plantings. A planting site without perennial weeds is essential for growing rhubarb. Perennial weeds can quickly build up to serious infestation and destroy your plants.

Propagation of rhubarb from seed is not recommended, as rhubarb seedlings do not come true from seeds. Buy named varieties or propagate with planting divisions obtained by splitting the crowns. Crowns formed during previous growing seasons can be divided. Split dormant crowns between large buds or "eyes" so that at least a 2 inch cross section of storage root is left with each bud. Very small buds will give small plants for the first few years after planting.

Do not pick rhubarb the first year of planting as the food from the leaves is needed to nourish the roots for the next year's growth. Make a light picking during the year following planting if the plants are vigorous. Beginning the second year following planting, the entire plant may be harvested.

When harvesting rhubarb, the cut the stalks at the soil line or pull them out individually. All of the stalks of a plant may be harvested at one time, or pulled out selectively over a 4 6 week period.

The edible portion of the plant is the very elongated and thickened leaf stalk. The length, width and colour of leaf stalks vary greatly among varieties (see Varieties).

The leaf blade contains a high content of oxalic acid, characterized by soluble salts, which can be quite poisonous. In the stalks, oxalic acid is present in smaller amounts and is largely in an insoluble salt form.

At relatively low temperatures for growth, stalks have been observed to develop more red colour, while at high temperatures, the green colour predominates. Stalk colour is largely variety specific.

Seedstalk development is normal in all varieties, but it is more common when cool temperatures occur in spring. The frequency of development varies greatly with the variety. Some varieties are not recommended because of their tendency to produce seedstalks continually.

Seedstalks begin to appear very early in spring, and if not cut off, the food energy drawn by the seedstalk will inhibit the production of leaves and petioles, thereby reducing vigour overall.

Varieties 1. German Wine - very vigorous variety that produces very large, green stalks; suitable only for juicing and wine products; second harvest in the same season is the highest in this variety; stalks are easy to pull. 2. Mcdonald - moderately red stalks; very good vigor; excellent for pie-filling products. 3. Early Sunrise - very similar to Mcdonald but vigor is moderately less; red is intense. 4. Victoria - not recommended because of its frequent habit of producing seedstalks; used almost exclusively for wintertime indoor forcing. 5. Cherry Wine - bright red stalks; almost free of seedstalk development; has moderate vigor. 6. Valentine - bright red stalks make this variety the most attractive; vigor is lacking somewhat; almost free of seedstalk development. 7. Crimson Red Cherry - not recommended because of its frequent habit of producing seedstalks. 8. Cherry Red - bright red stalks; similar to Cherry Wine; the plant lacks vigor when harvested twice per season; almost free of seedstalk development; stalks are hard to pull. 9. Holstein Red - bright red stalks; the plant lacks vigor and produces seedstalks continually; not recommended. 10. Canada Red - good vigor along with moderately red stalks; similar to Mcdonald. 11. Oregon Red - not recommended because of its frequent habit of producing seedstalks; weak red in stalks. 12. Strawberry - stalks are very light red; almost free of seedstalk development; moderate vigor. 13. Simonette - a very intense red-stemmed variety; field evaluation is incomplete. 14. Honey Red - a nice red-stemmed variety; field evaluation is incomplete. It has been generally observed that the redder the stalks, the less vigorous the plant. These varieties with the weaker red color seem more susceptible to a disease common in Alberta called redleaf.

Rhubarb Diseases Leaf spot, commonly called redleaf, is the only common disease that affects rhubarb in Utah. It appears as small, greenish-yellow areas on the upper surface of the leaves. These change to angular-shaped spots with white center with wide, reddish margins.

In severe cases, the red color becomes very prominent, the plant loses vigor and leaves droop. Eventually, the crown dies, usually the second or third season after symptoms show.

To control leaf spot, remove all infected leaves during the growing season and destroy them. If symptoms continue, dig and destroy the crown. The disease spreads by aphids feeding on infected plants and then subsequently feeding on healthy plants.

The disease is often confused with natural leaf dieback that occurs quickly at the end of the season. Redleaf-like symptoms occur in fall in response to low temperatures. True redleaf symptoms appear in June and July, beginning with a few leaves showing symptoms and getting worse each season.

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