Rhubarb

Description

Rhubarb is the name given to several species of herbaceous perennial plants in the genus Rheum, including R. rharbarum and R. rhaponticum (wild rhubarb), R. rhaponticum (garden rhubarb) and cultivated hybrid varieties designated as R. hybridum or Rheum × hybrium which are grown for their edible leaf stalks, or petioles. Rhubarb is a robust, clump forming plant. The large leaves are arranged in a rosette and have fleshy petioles which are often red in color and can reach 1–1.5 m (3.3–4.9 ft) in length The leaves are large and palmate with an irregular undulating edge. The plant produces small, green-white flowers on the end of an erect stem. Rhubarb plants can reach 1.5 m (4.9 ft) in height and 2 m (6.6 ft) in diameter and petioles can be harvested for many years. Rhubarb is sometimes also referred to as pieplant and likely originated from Northern China and Siberia.


Uses

The rhubarb petioles can be eaten fresh or cooked, usually with sugar to balance the sharp flavor of the plant. Rhubarb is a popular ingredient in pies and desserts.


Propagation


Basic requirements
Rhubarb grows best in temperate climates with cool summers and winters which result in the ground freezing. The plant requires winter temperatures below 4.4°C (40°F) to break dormancy. Rhubarb will grow optimally at temperatures of 15–20°C (59–68°F) and is adapted to high rainfall as long as there is adequate drainage. Plants will grow best in a fertile, well-draining soils rich in organic matter with a pH between 6.0 and 7.0.

Propagation
Rhubarb can be propagated from seed but it is more common to grow from whole crowns or cut pieces of the crown (divisions). Each division of the crown should possess at least one healthy bud. Crowns should be planted as soon as possible after purchasing/dividing to prevent them drying out. This is best performed in early Spring to allow the new plants to establish in the soil. Choose a site that receives full sun. An area that receives afternoon shade may be beneficial in warmer areas. Prepare the site for planting by loosening the soil with a fork to a depth of approximately 25 cm (10 in). Encorporate organic matter such as a good quality compost or well-aged manure into the soil prior to planting and a small amount of fertilizer. Rhubarb crowns and divisions Planting should be planted at a depth of 5 cm (2 in) leaving 1 m (3.3 ft) between plants and 1.5–1.8 m (5–6 ft) between rows. Once in the ground, tamp the soil firmly around the crowns and water deeply.

General care and maintenance
Rhubarb requires regular watering during dry weather. a layer of organic mulch such as straw applied over newly planted crowns will help to conserve soil moisture while suppressing weeds. The soil should be kept moist but not wet. Rhubarb should be fertilized with nitrogen to promote vigorous and healthy growth. Nitrogen can be supplied at planting through the addition of well composted manure or a good quality compost. Nitrogen side-dressings should be made at regular intervals throughout the growing season. Rates should be adjusted based on the results of a soil test.

Harvesting
Rhubarb should not be harvested in the first year after planting if the plant is to be maintained as a perennial. In the second year, stalks may be harvested as they mature. Leaves should be fully mature prior to harvest. Stalks should be harvested by hand cutting. Always ensure that foliage remains on the plant. Do not overharvest.


References

Bratsch, A. & Mainville, D. Rhubarb. Virginia Cooperative Extension. Available at: https://pubs.ext.vt.edu/438/438-110/4.... [Accessed 06 April 15]. Free to access.

Riofrio, M. Growing rhubarb in the home garden. The Ohio State University Extension. Available at: http://ohioline.osu.edu/hyg-fact/1000.... [Accessed 06 April 15]. Free to access.

Schrader, W. L. (2000). Rhubarb production in California. University of California Division of Agriculture and Natural Resources. Available at: http://anrcatalog.ucdavis.edu/pdf/802.... [Accessed 06 April 15]. Free to access.




Common Pests and Diseases

Gray mold
Botrytis cinerea

Symptoms
Gray to brown discoloration of leaves; water-soaked areas which develop white-gray fuzzy growth under humid conditions; red-brown water-soaked areas developing on stalks
Cause
Fungus
Comments
Favors cool, damp, poorly ventilated conditions
Management
Allow plants adequate space when planting to promote good air circulation around the plants; application of appropriate fungicides can help to control the disease

Slugs
Various

Symptoms
Irregularly shaped holes in leaves and stems; flowers and fruit may also be damaged if present; if infestation is severe, leaves may be shredded; slime trails present on rocks, walkways, soil and plant foliage; several slug and snail species are common garden pests; slugs are dark gray to black in color and can range in size from 2.5 to 10 cm (1-4 in)
Cause
Mollusc
Comments
Slugs prefer moist, shaded habitats and will shelter in weeds or organic trash; adults may deposit eggs in the soil throughout the season; damage to plants can be extensive
Management
Practice good garden sanitation by removing garden trash, weeds and plant debris to promote good air circulation and reduce moist habitat for slugs and snails; handpick slugs at night to decrease population; spread wood ashes or eggshells around plants; attract molluscs by leaving out organic matter such as lettuce or grapefruit skins, destroy any found feeding on lure; sink shallow dishes filled with beer into the soil to attract and drown the molluscs; chemical controls include ferrous phosphate for organic gardens and metaldehyde (e.g. Buggeta) and carbaryl (e.g Sevin bait) for non-organic growers

Phytopthora root and crown rot
Phytophthora spp.

Symptoms
Depressed, brown lesions at base of stalks; leaves wilting; entire stalks collapse; crown and roots turn black and disintegrate
Cause
Oomycete
Comments
Disease emergence favors cool, rainy weather
Management
Plant rhubarb in well draining soils; avoid planting in soils where rhubarb has been grown in the past 4-5 years; mounding the soil can help to promote drainage around the plant