FS360E Growing Rhubarb in Home Gardens (Home Garden Series)

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Culinary rhubarb (Rheum × cultorum, Foust and Marshall, 1991)
is an herbaceous perennial that is grown for its petiole (the stalk
connecting the leaf to the stem) and is perhaps the only
commonly grown vegetable treated as a fruit in the kitchen. This
publication describes the best methods for growing and
sustaining healthy rhubarb plants in the home garden.
Introduction
Rhubarb (Rheum) species are native to parts of Europe and Asia
and have been widely cultivated as culinary crops in temperate
areas all over the world. The short stems of these herbaceous
perennials (Figure 1) are hidden by long, sturdy petioles
(commonly referred to as stalks) bearing large leaves (Figure 2).
Rhubarb is a temperate crop—that is, it requires cold
temperatures during the winter to stimulate growth in the spring
(Schrader 2000). Once established, rhubarb is a vigorous crop
that can live for years and produces “stalks” that are cheaper and
of better quality than store-bought (Miles 2013).
Planting Site Selection
Because rhubarb is a perennial plant and will increase in size
each year, it is best to grow it as a landscape plant rather than in
an annual bed. Once planted, it should not be disturbed unless
crown divisions are being made. The diameter of a single
rhubarb plant can reach eight feet or more (Figure 3), so give
each plant plenty of space in full sun for best production. Like
most landscape plants, rhubarb performs best in a well-drained,
aerated soil. Avoid planting in areas where drainage problems
are known to exist.
If you have not had a soil test done for nutrient and organic
matter levels, you should do one before planting any perennial.
Many home gardens and landscapes have excessive levels of
nutrients, and this information will aid you in knowing whether
you need to add fertilizer, compost, or any other source of
nutrients. University and governmental soil testing laboratories
are recommended, as they will provide objective data and
recommendations relevant to your home garden situation.
Figure 1. The stem of this plant, where young leaves are emerging, is barely
visible among the mature leaves. Photo by Linda-Chalker-Scott.
GROWING RHUBARB
IN HOME GARDENS

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Figure 2. Rhubarb leaf and petiole. Photo by Linda Chalker-Scott.
Figure 3. The spread of this rhubarb crown is over eight feet. Note, also, the
arborist wood chip mulch. Photo by Linda Chalker-Scott.
Plant Selection
Rhubarb is usually purchased as a crown division, so these
clonal plants will be identical to the parent. Seeds are also
available, but since they are genetically variable, a packet of
seeds might result in plants with stalks ranging from green to
pink speckled to red. Such color variants have been propagated
vegetatively to develop the many cultivars available to gardeners
(Table 1).
Table 1. Common rhubarb cultivars with their stalk colors.
Green
Pink Speckles
Red
‘Riverside Giant’
‘German Wine’
‘Canada Red’
‘MacDonald’
‘Cherry Red’
‘Strawberry’
‘Crimson Cherry’
‘Victoria’
‘Crimson Red’
‘Crimson Wine’
‘Tilden’
‘Valentine’
Planting Guidelines
As with other perennials, rhubarb will do best when planted in
the fall when the plant is dormant. However, roots will be
available in garden stores and through mail order stores during
the winter and early spring. This means that root reserves will be
directed to root growth and establishment, because roots do not
go dormant. This is also the best time of year to make crown
divisions. Planting or dividing in the spring when new leaves are
emerging will result in reduced resources for root growth and
subsequent water stress for new and existing leaves.
All container media should be removed from purchased roots,
either by shaking it off or soaking the root ball in a container of
water. Place the exposed root mass in a hole that is no deeper
than the root mass and at least as wide. The planting hole will be
shallow and wide, like a saucer. Place the root mass in the hole
and backfill with the same soil that came out of the hole. Do not
add amendments of any sort; your goal is to get the roots in
contact with the native soil, and amendments interfere with this
activity. Add water and more soil as needed, while adjusting the
plant if needed to keep the crown above grade. Do not press or
stomp the soil during planting. Let water move through the soil
naturally to create a continuous medium (this is sometimes
called “mudding in”). Plants growing in containers are also
available from garden stores in early spring. Planting hole
preparation will be the same as bare root starts but retain the
container soil mix around the root when planting.
After planting, add about four inches of coarse organic mulch to
the soil surface up to, but not covering, the crown (Figure 3).
Arborist wood chips, available from tree services, or straw are
excellent choices as they allow for oxygen and water movement,
suppress weeds, and moderate soil temperatures (Chalker-Scott
2015). Do not add any transplant supplements, including
fertilizers, unless you have soil test results showing a nutrient
deficiency. Rhubarb will thrive for many years as long as the
mulch layer is maintained and sufficient water is provided
during the growing season.
Plant Maintenance
Once established, rhubarb requires little care other than
maintaining a mulch layer and irrigation. Because rhubarb is a
cool season plant, it will experience stress as summer
temperatures rise. Leaf production is best when daily
temperatures are in the mid-70s and evening temperatures in the
mid-50s (Schrader 2000). Once temperatures exceed 90°F, leaf
production will slow; during this time it is especially important
to provide sufficient water or the plant might enter summer
dormancy.
With the onset of cold fall evenings, rhubarb leaves will senesce
and should be removed once they have turned brown. Before
winter, be sure to add additional wood chip mulch to the root
zone to maintain a four-inch depth. This will prevent weed
establishment over the winter.

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As your plant matures, it may become too large for its space.
Dividing the plant in the fall will renew the vigor of the
remaining crown, and the divisions can be planted elsewhere.
Pest and Disease Problems
Rhubarb suffers from few insect or disease problems, and many
of these can be avoided by proper landscape management.
Growing rhubarb as an individual plant in a diverse landscape
rather than as a monoculture means that you have a host of
beneficial organisms, including predators, that can reduce pest
insects. Aphid species may be present that can transmit viruses
(Pantoja et al. 2010). Use a garden hose to reduce aphid
populations on rhubarb leaves to minimize this possibility.
Reported diseases, especially root rots caused by Phytophthora,
Pythium, Rhizoctonia, and Botrytis, can be avoided by planting
in well-drained soils (Schrader 2000). Avoid the use of
pesticides and unnecessary fertilizers when possible.
If problems do occur on leaves or stalks, be sure to take samples
to your county Master Gardener office for help in identifying the
problem and treating it appropriately.
Harvest and Storage of
Rhubarb
Rhubarb can be harvested as soon as there is vigorous leaf
production. Wait until the second season before harvesting. You
don’t want to harvest too much at any one time, as this will
decrease the plant’s vigor. When leaves begin to lie horizontally,
this is a good indication that they are ready to be removed, as
they are being displaced by new leaves (Figure 4).
Harvest the largest stalks first. To remove a stalk, grasp the base
firmly (Figure 5) and pull while rocking your hand side to side.
This should result in the entire stalk being removed (Figure 6).
Avoid breaking or cutting the stalks, as these cut surfaces could
allow pathogens and pests to enter. A rhubarb plant may produce
one or more stalks that produce large white flowers. These will
have poor quality and should be harvested and discarded so the
plant does not expend resources on these stalks.
Figure 4. Basal leaves become more horizontal as new leaves emerge. Photo by
Linda Chalker-Scott.
Figure 5. Firmly grasp the petiole as close to the base as possible. Photo by
Linda Chalker-Scott.
Figure 6. Successful removal of the petiole avoids breakage or tearing. Photo by
Linda Chalker-Scott.

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Next, remove the leaf from the stalk. The leaf has toxic levels of
oxalic acid, and its consumption should be avoided. Cut the top
of the stalk away from the entire leaf (Figure 7) and discard. The
leaves can be safely composted as oxalic acid will not affect
microbes. The stalk can now be sliced and used for cooking. For
storage, slice the stalks and refrigerate for a few weeks, or freeze
indefinitely.
Figure 7. Remove the entire leaf from the petiole and discard. Photo by Linda
Chalker-Scott.
Harvest rhubarb throughout the growing season, but retain some
leaves on the plant in the summer and fall to allow the roots to
extract and retain nutrition from those leaves for next year’s
growth. The leaves and stalks die back once freezing
temperatures arrive, and they can be discarded once they have
detached themselves from the stalk. The quality of freeze-
damaged petioles is poor, and it is best to discard them, but the
belief that freeze-damaged leaves release oxalic acid into the
stalks is not supported by any published research.
Using Rhubarb in the
Kitchen
Rhubarb is best used in cooking, not as raw juice. While rhubarb
stalks contain low levels of oxalic acid, oxalic acid is
concentrated in rhubarb juice (Siener et al. 2016). Rhubarb
stalks, particularly red ones, contain high levels of anthocyanins,
which are powerful antioxidants. To maintain both color and
antioxidant activity, baking and slow stewing are the
recommended methods of preparing rhubarb (McDougall et al.
2010).
References
Chalker-Scott, L. 2015. Using Arborist Wood Chips as a
Landscape Mulch (Home Garden Series). Washington State
University Extension Publication FS160E. Washington State
University.
Foust, C.M., and D.E. Marshall. 1991. Culinary Rhubarb
Production in North America: History and Recent Statistics.
HortScience 26(11):1360–1363.
McDougall, G.J., P. Dobson, and N. Jordan-Mahy. 2010. Effect
of Different Cooking Regimes on Rhubarb Polyphenols. Food
Chemistry 119(2):758–764.
Miles, C. 2013. Home Vegetable Gardening in Washington
(Home Garden Series). Washington State University Extension
Publication EM057E. Washington State University.
Pantoja, A., A.M. Hagerty, S.Y. Emmert, J.C. Kuhl, K. Pike,
J.M. Alvarez, and A. Jensen. 2010. Aphids (Hemiptera:
Aphididae) Associated with Rhubarb (Rheum spp.) in the
Matanuska Valley, Alaska: Species Composition, Seasonal
Abundance, and Potential Virus Vectors. Journal of the
Entomological Society of British Columbia 107:75–81.
Schrader, W.L. 2000. Rhubarb Production in California.
University of California Division of Agriculture and Natural
Resources Publication 8020. University of California.
Siener, R., A. Seidler, S. Voss, and A. Hesse. 2016. The Oxalate
Content of Fruit and Vegetable Juices, Nectars and Drinks.
Journal of Food Composition and Analysis 45:108–112.

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By,
Linda Chalker-Scott, Professor and Extension Specialist, Department of Horticulture,
Washington State University
FS360E
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