E. S. Oplinger1, E. A. Oelke2, A. R. Kaminski1,
S. M. Combs1, J. D. Doll1, and R. T. Schuler1
1Departments of Agronomy, Soil Science and Agriculture Engineering, College
of Agricultural and Life Sciences and Cooperative Extension Service, University
of Wisconsin-Madison, WI 53706.
2Department of Agronomy and Plant Genetics, University of Minnesota,
St. Paul, MN 55108.
The castorbean plant (Ricinus communis) has been cultivated for centuries
for the oil produced by its seeds. The Egyptians burned castor oil in their lamps
more than 4,000 years ago.
Thought to be native to tropical Africa, the plant is a member of the spurge family.
The seeds with hulls removed contain 35 to 55% oil. The seeds, leaves, and stems
of the plant contain ricin and ricinine, which are poisonous to humans and animals.
Eating a castorbean causes nausea, and eating several may cause death. These toxic
compounds are not present in the oil.
Castorbeans are grown on a limited scale in the United States. Demand for the crop
peaked in the early 1950s, when the federal government wished to increase supplies
of castor oil for military applications in the event of a national emergency. The
government guaranteed farmers, particularly in the Southwest, ten cents per pound
for the seeds, which were grown under contract with castor oil processors.
The castorbean plant grows well in soil of medium texture. It is best adapted to
southeastern Kansas, Missouri, southern Illinois, southern Indiana, Tennessee, Kentucky,
and parts of Oklahoma and Texas. With irrigation, it also grows well in the Southwest.
In the United States, castor oil has been used by the military in aircraft lubricants,
hydraulic fluids, and in the manufacture of explosives. It has also been used in
the synthesis of soaps, linoleum, printer's ink, nylon, varnishes, enamels, paints,
and electrical insulations. Textile scientists have used sulphonated castor oil
in the dyeing and finishing of fabrics and leather. The most infamous application
of castor oil may have been as a purgative popular for the treatment or prevention
of many ailments in the first half of the twentieth century.
Castorbean meal is included as a protein source in feed for swine. Castorbean pomace,
or meal, the residue left after the oil has been extracted from the seeds, has been
included in mixed fertilizer. This product contains the ricin and ricinine from
the seeds. Certain varieties of castorbean plants are grown as ornamentals.
III. Growth Habits:
In the tropics, the castorbean plant is a perennial. It is grown as an annual in
temperate regions, however, requiring a growing season of 140 to 180 days.
Germination is slow. Seedlings will emerge 10 to 21 days after planting. Commercial
varieties grow to a height of 3 to 10 ft.
The plant consists of several stems or branches, each terminated by a spike. The
mature spike is six to 12 in. long. In some varieties, female flowers are on the
upper part of the spike and male flowers on the lower part. Other varieties have
male and female flowers interspersed on the spike. Varieties with spikes of only
female flowers have made possible the production of hybrid seed. Male flowers drop
off the spike after pollination.
The lower spikes on the plant mature first, followed by the upper spikes. Each spike
bears 15 to 80 capsules, which may be prickly or smooth on the outer surface. The
capsules, which develop from the female flowers, contain three seeds each and explode
The seeds may be egg-shaped, oblong, or round, usually with an enlargement on one
end, called the caruncle. Seeds vary in size, but most commercial varieties average
1,000 to 1,500 seeds/lb.
The plant is not a legume, as its name would imply. It has no soil-improving value
other than that of any rotation crop.
IV. Environment Requirements:
Castorbeans grow best where temperatures remain fairly high throughout the growing
season of 140 to 180 days. The soil must be able to warm up early in the spring.
The seed may fail to set, however, if the temperature stays above 100oF
for an extended period.
The crop requires a loamy soil of medium texture. Castorbeans do well on either
alkaline or acid soils, as long as the subsoil is permeable and there is good drainage.
Seed will not set if soil moisture is inadequate. Castorbeans should not be planted
in an area that is subject to erosion.
C. Seed Preparation and Germination:
Seeds should be cleaned to remove foreign material, seeds with attached hulls, and
damaged seeds. They should also be treated with a fungicide before planting. This
is particularly important where there is a risk of low spring temperatures and high
soil moisture immediately after planting. Thiram is the only registered seed treatment
fungicide for use on castorbeans.
Castorbeans are poisonous for animals and humans. In addition, inhaling dust from
the seeds may cause allergic reactions in some individuals. Seed treatment should
be performed carefully to minimize dust and to avoid contamination of food and livestock
feed. Children should be kept away from castorbean storage areas, and adults working
with the seeds and plants should be warned of their poisonous properties.
V. Cultural Practices:
A. Seedbed Preparation:
To prepare the seedbed, plow or disk the land. Be sure the soil is moist at the
planting depth of one to three in.
B. Seeding Date:
Castorbeans should be planted in early May, about the same time as corn. Seedlings
will emerge in 10 to 21 days.
C. Method and Rate of Seeding:
Good stands of castorbeans require fairly heavy planting rates, because germination
of the seed is usually rather low. Seeding at 10 to 14 lb/acre will give a good
stand, depending on the seed size and the height of the variety. Row width should
be 38 to 40 in. with 8 to 12 in. between plants. Because of differences in germination
rates and plant size, growers should calculate rates based on the seed lot. Seeds
should be planted at a depth of 12 to 3 in.
Because castorbeans are oily and easily broken, they can clog machinery and cause
irregular spacing. Most corn planters with an air metering system should perform
well. Planters using metering plates will require plates with proper cell size.
Always check the planting unit to ensure that excessive bean cracking or crushing
is not occurring during planting.
D. Fertility and Lime Requirements:
Castorbeans grow well on slightly alkaline or acid soils. The most important factor
in fertility level is the supply of nitrogen in the soil. Insufficient nitrogen
results in reduced castorbean yields. Excessive nitrogen produces heavy vegetative
growth with little or no increase in seed yield.
The amount of nitrogen required by castorbeans depends on the soil organic matter
content as shown in Table 1. Preplant and sidedress applications of nitrogen may
be beneficial at the higher application rates or on lighter-textured soils.
Table 1. Nitrogen recommendations for castorbeans.
Soil Organic Matter
Nitrogen Application Rate
-- % --
-- lb/acre --
2 - 4.9
5 – 10
In general, castorbeans require the same amount of nutrients as other low-demand
field crops. For typical silt loam soils testing in the optimum range (6 to 10 ppm
P; 81 to 100 ppm K), approximately 20 lb P2O5 and 40 lb K2O
should be applied per acre. If soil tests are below optimum, approximately 5 lbs
P2O5 and 20 to 30 lb K2O should be applied in addition
to the previous amounts. Castorbeans do not generally respond to phosphorus, and
excess soil phosphorus levels can actually decrease yields. Therefore, do not apply
P2O5 except where soils test in the optimum or below optimum
level for extractable P.
E. Variety Selection:
Castorbean varieties have been developed to produce large yields of seed with a
single harvest. The tall varieties may reach a height of 10 ft or more. The dwarf
types seldom exceed four or five ft.
No information is available about the adaptability of varieties to the Upper Midwest.
F. Weed Control:
The slow emergence and early growth of castorbeans means the plants are not strong
competitors against weeds. Rotary hoeing during the first few weeks after planting,
followed by row cultivation should provide acceptable control. Because the main
lateral roots of the castorbean plant are near the soil surface, cultivation should
be shallow. At the present time, herbicides are not registered for controlling weeds
in castorbeans in Wisconsin or Minnesota.
G. Diseases and Their Control:
Resistance to various diseases varies among castorbean varieties. During periods
of heavy rains or dews, capsule molds, Alternaria leaf spot and bacterial leaf spot
may occur. Alternaria leaf spot is more severe in nitrogen-starved plants. Other
diseases may occur, particularly in wet seasons. To help prevent disease problems,
a good rotation program and treatment of seed with a fungicide prior to planting
are recommended. Thiram is the only registered seed treatment fungicide.
H. Insects and Other Predators and Their Control:
Though leaf- and stem-feeding insects usually do not cause serious damage to castorbean
plants, cutworms and wire worms may reduce stands. Stink bugs, corn earworms, webworms,
caterpillars, grasshoppers, thrips, spider mites, leaf miners, Lygus bugs, the yellow-striped
army worm, and the European corn borer also may attack the plants.
The castorbean crop is ready for harvesting when all the capsules are dry and the
leaves have fallen from the plants. Ideally, harvesting should begin 10 to 14 days
after the first killing frost. If killing frosts will not permit completion of harvesting
before winter, a chemical defoliant may be applied 10 to 15 days ahead of the desired
harvest date. Defoliants tend to reduce yields, however. Delay in harvesting after
the crop is ready may result in losses from "shattering," in which the seeds pop
out of the capsules.
Since castorbeans are very susceptible to cracking and splitting during harvest,
adjustment of the combine cylinder speed and cylinder-concave clearance is very
important. Usually, a low cylinder speed and wide cylinder concave clearance are
recommended. Combine operators should frequently inspect harvested beans for breakage.
Weeds cause problems in the castorbean harvest. They may clog machinery or push
in front of the harvester and cause shattering of the castorbeans. Volunteer corn
plants present no special problem in the harvesting operations, but do add foreign
material to the yield.
After harvest, break up the stalks mechanically and work them into the soil. The
stalks deteriorate rapidly and furnish organic matter. Castorbean hulls, which are
scattered over the field during harvest, are about equal to barnyard manure in fertilizer
Seeds left in the field after harvest may cause a volunteer problem in the next
year's crop. Waiting until seeds germinate and then disking the young plants down
will prevent this to some extent. Follow castorbeans with a row crop or a grain
crop, for which the volunteer castorbean plants will not present a problem.
J. Drying and Storage:
Moisture content, foreign material, and cracked or broken beans are considered in
grading the seed. Ideally, castorbeans should be stored at less than 6% moisture.
VI. Yield Potential and Performance Results:
Yields vary depending on variety, the season, cultural conditions, and the care
exercised in harvesting. No information is available concerning castorbean yields
in Wisconsin and Minnesota. However, yields of about 2,200 lb/acre have been produced
in Nebraska tests.
VII. Economics of Production and Markets:
Castorbean markets are limited. The crop should be grown only after identifying
a market, and preferably after arranging a contract with a buyer.
VIII. Information Sources:
* Castorbean Production. 1960. U.S.D.A. Farmers' Bulletin No. 2041