Growing Rhubarb

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The Rhubarb Compendium
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6 - Growing Rhubarb

Rhubarb is a cool season, perennial plant that is very winter hardy and resistant to drought. Its crop is produced from crowns consisting of fleshy rhizomes and buds. Following a season of growth the rhubarb crown becomes dormant and temperatures below 40­ F are required to stimulate bud break and subsequent growth. The first shoots to appear in the spring are edible petioles and leaves. These emerge sequentially as long as temperatures remain cool (below 90­ F). As temperatures increase, top growth is suppressed, even appearing dormant in periods of extreme heat. With declining temperatures in later summer, foliage growth resumes. 1

6.1 - Climate and Growing Region

Rhubarb is a cool season, perennial crop. It requires temperatures below 40­ F to break dormancy and to stimulate spring growth and summer temperatures averaging less than 75­ F for vigorous vegetative growth. The Northern U.S. and Canada are well suited for rhubarb production. In the United states it grows best in the northern states from Maine south to Illinois and west to Washington state. Once planted, rhubarb plantings remain productive for 8 to 15 years.

In the United States, commercial production is concentrated in Washington (275 Acres), Oregon (200 Acres), and Michigan (200 Acres), with small commercial acreage in many northern states field and greenhouse forced production. A good commercial yield is 15 tons and an exceptional yield is about 18 tons. Red varieties usually yield about 50% of the green types; however, if the crop is harvested twice in one year, total yields will increase about 50%.

Rhubarb can not be very successfully grown in the southern regions of the United States, although there are exceptions (see Growing Rhubarb as an annual). Rhubarb is a popular garden vegetable in northern areas of the United States but unfortunately will not do well in hot, dry summers of the south. If it survives the heat it will not grow well will produce only thin leaf stalks which are spindly and lack color. Rhubarb will wilt very quickly on hot days (over 90­ F). There has been mention of an unknown variety of rhubarb with large green petioles that thrives in the Panhandle north of Amarillo (Texas). 2 3 4

6.2 - Soil

Rhubarb tolerates most soils but grows best on fertile, well-drained soils that are high in organic matter. A clean planting site is essential for the cultivation of rhubarb since no herbicides are registered for use on rhubarb. Small areas of perennial weeds can quickly build up to serious proportions. To prevent this, all perennial weeds should be killed the year before planting. The fields should be cultivated in the spring and after cutting, and hand hoeing may also be necessary. Rhubarb is relatively free of insect and disease problems (see Problems). 5 6 7

6.3 - Fertilization

Rhubarb is rather tolerant of soil acidity but does best in slightly to moderately acid soil. The crop can tolerate soil pH as low as 5.0; however, maximum yields are attained at a pH of 6.0 to 6.8. Liberal quantities of fertilizer are needed.

Rhubarb responds well to fertilizers. The quality of the crop harvested depends to a large extent on the care and fertilization received. Commercial growing requires about 1500 pounds of 10-10-10 per acre before planting. Home gardeners should give each plant 1 cup of 10-10-10 fertilizer each spring, applied in a circle around the plant when growth starts. Fertilize each year and cultivate shallowly as often as necessary to remove weeds.

Manure is an extremely valuable source of organic matter as it helps to conserve moisture, preserves the soil structure, and makes nutrients readily available. Fifteen tons of manure should be applied per acre before planting for commercial growing or one to two shovels per plant for home gardeners. An application of composted manure or leaves is beneficial in late fall and early winter, but do not cover the crowns as this may promote rotting. Fresh manure should not be used as this will burn the tender rhubarb plants. 8 9 10 11 12

6.4 - Planting and Spacing

Plant rhubarb roots in early spring. Planting seeds is not recommended as it may take too long for the plants to become established, and the seedlings would not come true to color and size, if that is important to you (otherwise see Growing Rhubarb as an annual).

Space rhubarb roots 24 to 48 inches apart in rows 3 to 4 feet apart for commercial growing. These distances can be decreased to 36 inches for plants in rows and rows for smaller gardens (non commercial). Much smaller than this will seriously crowd the plants and result in a diminished crop and increase the likelihood of spreading disease. A 2-3 year old plant, the Victoria variety can be 4 feet (1.25 meter) in diameter and  3 feet (1 meter) tall. Plant the roots with the crown bud 2 inches (5 cm) below the surface of the soil. The hole for the crown should be dug extra large and composted manure, peat moss or dairy organic should be mixed with the soil to be placed around the roots. Firm the soil around the roots but keep it loose over the buds. Water the crowns after planting. Give the plant 1/4 cup of 5-10-10 worked in to the top 10 inches of soil at planting time. Good garden drainage is essential in growing rhubarb. For home gardeners, planting in raised beds helps ensure against rotting of the crowns. Crowns will have a longevity of many years, but because of diseases and insects, it is Normal to reset a bed after 4-5 years (see Dividing and Thinning). 13 14 15 16 17

6.5 - Growing

6.5.1 - General

Rhubarb responds to good care and watering. Remove the flower stalks as they are seen. During the first year of planting, the stalks should not be picked, since food from the leaves is needed to nourish the roots for the next year’s growth. One light picking may be taken during the year following planting if the plants are vigorous, and beginning the second year following planting, the entire plant may be harvested. When harvesting rhubarb, the first step is to cut the stalks at the soil line or simply 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. After the stalks are cut, the leaves may be removed. For the home (small) gardener, rhubarb will tolerate a fair amount of neglect and still thrive, they are very tough plants. 18 19 20

6.5.2 - Growing Season

The rhubarb season (in the United States) runs from April to September, although it can be grown forced (see Forcing in winter) which accounts for its availability early in the year when other crops are scarce. Early forced rhubarb has a distinctive bright pink color and delicate flavor. Outdoor rhubarb is a little darker in color. 12

Refrain from harvesting rhubarb the first year after planting. Each plant needs time to build up food reserves in the root to produce thick, robust stems. 28

Established rhubarb plants can be coaxed into early outdoor production by covering plants with clear plastic in the early spring, before the crown starts to grow. As growth starts, cut 1/4 inch ventilation holes in the plastic. As leaves get larger, cut the plastic to keep the leaves free. 21

6.5.3 - Frost Damage

Rhubarb hit by a frost or freeze can still be eaten provided the stalks are still firm and upright. Leaf injury may be noticeable with some brown or black discoloration on the edges. If the stems appear soft and mushy, do not eat them. Severe cold injury may cause the oxalic acid crystals in the leaves to migrate to the stalks increasing the likelihood of poisoning problems. If in doubt about the safety of eating the stalks, don’t. Cut those stalks off and compost them. Allow new stalks to develop before eating, or if it is the end of the growing season, try forcing some rhubarb indoors (see Forcing in winter). 22 23 24

6.5.4 - How do I prepare my rhubarb plants for winter

Rhubarb needs cold to trigger spring growth. Rhubarb tolerates very cold (-20 F) very well. Collect the last few stalks after the first hard frost and throw them on the compost pile. Then spread a layer (2-3”) or compost (or leaves or hay) to prevent winter winds from drying out your roots. You don’t need to do much.

6.6 - What do I do with the seedpods?

Rhubarb plants will occasionally send up seed stalks with flowers in the middle of the plants. These stalks can occur due to natural maturity of the plants. Some varieties of rhubarb are more likely to flower than others. Victoria is known to be a flowering type. Flowering will reduce the vigor of the plant. Energy is funneled into the stalks instead of new growth for rhubarb growth as a vegetable. If the plant is grown as an ornamental the tall stalks of flowers (Victoria has white (greenish)) is quite impressive. The flower and seed stalks should be cut out as soon as they start forming. The plant may still continue to produce the flower stalks so keep cutting. The plants do NOT become poisonous after flowering starts. The leaf stalks can still be cut and used and the leaves themselves are always poisonous. 25 26 27 28

6.7 - Can I compost my rhubarb leaves

Many folks have been concerned about adding rhubarb leaves to their compost piles. If the leaves are poisonous, they must be bad for compost as well, since rhubarb stalks contain a high concentration of oxalic acid which slightly toxic. What actually occurs when rhubarb is added to a compost pile is that the oxalic acid is decomposed and pH balanced rather quickly. People do not eat compost piles as a rule anyway, and even if a child were to eat compost dirt, there would be problems other than residuals from the decomposing rhubarb stalks. Experience has also shown that the level of acid does not inhibit the microbial action of composting. Compost piles which were nearly all rhubarb leaves and stalks have decomposed very nicely and the compost has behaved like ordinary compost and no inhibition of plant growth was noticed from the compost. Note that some items are a problem for composting including: eucalyptus leaves and bark, omnivore (cat and dog) pet feces, diapers, meat scraps, and treated lumber. 29

6.8 - Do I need to thin my overgrown rhubarb?

Established clumps will have to be trimmed every 4 to 5 years or when the stalks get small and spindly or when the crown is visibly crowded. This will help the plant to keep growing nice thick stems. This is done by digging around and trimming the crown down to 4 or 5 buds. You can also use this opportunity to divide your plant into more plants. You may encounter is rot in the crowns from excessive water in the crown area. If so, destroy these plants. 30 31

Readers of The Rhubarb Compendium may be interested in…

Maria Rodale’s Organic Gardening: Your Seasonal Companion to Creating a Beautiful and Delicious Garden

Maria Rodale

Maria Rodale, who comes to organic gardening naturally (her father and grandfather, who founded Rodale Press, were famously passionate organic gardeners) felt for many years that while there was plenty of good information about organic gardening, there was neither an existing primer that taught all the very basics nor a book that showed that organic gardening can be a beautiful, sophisticated way to plant.  So she wrote this one, which, from the discussion of planning your garden on graph paper and the tips on digging up grass to the recipes for using the fall harvest, is utterly, seductively beautiful.  Rodale shows great sense in deciding what’s important to new gardeners and those just deciding to go organic. Pests, both animal and plant, are the great fear of potential organic gardeners, and many pages in the book are devoted to weeding effectively, beating the bugs, and gently monitoring the animal population (getting a dog or cat is one good, low-effort solution to keeping a number of destructive small mammals out of the root systems).  It’s a joy to read, and will inspire many a fresh organic tomato. [b08]

Footnotes:

1. Untitled, http://agweb.clemson.edu/Hort/drd/Rhubarb.html- 03900106 (Growing Rhubarb), http://lep.cl.msu.edu/msueimp/htdoc/mod03/03900106.html- Rhubarb, http://aggie-horticulture.tamu.edu/plantanswers/vegetables/rhubarb.html- Untitled, http://agweb.clemson.edu/Hort/drd/Rhubarb.html- 03900106 (Growing Rhubarb), http://lep.cl.msu.edu/msueimp/htdoc/mod03/03900106.html- 01701479 (Rhubarb, Pieplant.), http://lep.cl.msu.edu/msueimp/htdoc/mod03/01701479.html- Untitled, http://agweb.clemson.edu/Hort/drd/Rhubarb.html- 03900106 (Growing Rhubarb), http://lep.cl.msu.edu/msueimp/htdoc/mod03/03900106.html- 01701479 (Rhubarb, Pieplant.), http://lep.cl.msu.edu/msueimp/htdoc/mod03/01701479.html- Rhubarb - early spring is time to plant, http://wwwagcomm.ads.orst.edu/AgComWebFile/Garden/vegetable/rhubarb.html- RHUBARB - Rheum rhaponticum, http://uaexsun.uaex.arknet.edu/Vegfacs/rhubarb.html- Untitled, http://agweb.clemson.edu/Hort/drd/Rhubarb.html- 03900106 (Growing Rhubarb), http://lep.cl.msu.edu/msueimp/htdoc/mod03/03900106.html- Rhubarb, http://www.lysator.liu.se/ftp/pub/gardening/Edibles/rhubarb, An email From: JOHN HEIM, Subject: Rhubarb care, Date: 26 May 92 19:03:59 GMT- 01701479 (Rhubarb, Pieplant.), http://lep.cl.msu.edu/msueimp/htdoc/mod03/01701479.html- RHUBARB - Rheum rhaponticum, http://uaexsun.uaex.arknet.edu/Vegfacs/rhubarb.html- Untitled, http://agweb.clemson.edu/Hort/drd/Rhubarb.html- 03900106 (Growing Rhubarb), http://lep.cl.msu.edu/msueimp/htdoc/mod03/03900106.html- 01701479 (Rhubarb, Pieplant.), http://lep.cl.msu.edu/msueimp/htdoc/mod03/01701479.html- rhubarb2, http://ftp.lysator.liu.se/pub/gardening/Edibles/rhubarb2, a USENET posting From: Barry Carlson, Subject: Rhubarb, Date: Thu, 20 May 1993 01:39:06 GMT- Rhubarb - early spring is time to plant, http://wwwagcomm.ads.orst.edu/AgComWebFile/Garden/vegetable/rhubarb.html- Veggies Unit: your on-line guide to vegetarianism, http://www.honors.indiana.edu:80/~veggie/recipes.cgi/- Rhubarb — Frost Damage, http://www.ag.uiuc.edu/~robsond/solutions/horticulture/docs/rhubarb2.html, Illinois Cooperative Extension Service Horticulture Solution Series- Rhubarb (a description), http://www.ag.uiuc.edu/~robsond/solutions/horticulture/docs/rhubarb1.html- Veggies Unit: your on-line guide to vegetarianism, http://www.honors.indiana.edu:80/~veggie/recipes.cgi/- Rhubarb — Seed Stalks, http://www.ag.uiuc.edu/~robsond/solutions/horticulture/docs/rhubarb3.html- Rhubarb (a description), http://www.ag.uiuc.edu/~robsond/solutions/horticulture/docs/rhubarb1.html- RHUBARB - Rheum rhaponticum, http://uaexsun.uaex.arknet.edu/Vegfacs/rhubarb.html- A USENET posting to the Newsgroup rec.gardens on 1996/01/29 by Jim McNelly (Jim the Compost Man)  on the subject of “Re: Compost and Rhubarb Leaves” Look up this message at Deja.com- Rhubarb, http://www.lysator.liu.se/ftp/pub/gardening/Edibles/rhubarb, An email From: JOHN HEIM, Subject: Rhubarb care, Date: 26 May 92 19:03:59 GMT- 01701479 (Rhubarb, Pieplant.), http://lep.cl.msu.edu/msueimp/htdoc/mod03/01701479.html

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Updated on September 1, 2004
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