By: Connie Krochmal
The various rapeseeds are also known as rape. They have been in cultivation since 2000 B.C. or so in Asia. Grown much like grains, these bee plants are members of the cabbage or crucifer family. Different types of rapeseed are grown specifically for various purposes, although the plants are quite similar. This is a profitable crop for growers more so than Winter wheat in some locations.
The oil is used for cooking, fuel, and industrial purposes, while the seeds and seed meal are fed to animals. In the U.S., these were widely grown during World War II. In the late 1980s and 1990s, they were a popular crop in the South.
In recent years, the oil from the various canola varieties of rapeseed has been touted as being heart-healthy. The first canola varieties, which were hybrids of mustard and various rapeseed species, were bred in Canada beginning in 1974. These are called ‘double lows,’ since they’re low in erucic acid and glucosinolates, which are harmful to humans and other animals. ‘Double-low’ European varieties were later released.
General Description
Generally, rapeseed pretty much resembles mustard. These broadleaf, slender, erect, vigorous plants are usually grown as hardy annuals. Although rapeseeds can vary somewhat in height according to the species, variety, and planting time, they’re typically three to five feet in height. These feature long taproots and fibrous root systems that are close to the soil surface.
Covered with a waxy bloom, the much branched plants form a thin stand. The foliage initially emerges as a thick rosette very close to the ground. For Fall-planted crops, the plants go dormant as temperatures drop and resume growth the following Spring.
Rapeseed blossoms are quite similar to those of mustard. A field of rapeseed in full bloom is spectacular. With four petals and sepals, the flowers form flat topped clusters. The two whorls of stamens can vary in length within the flower.
Fall planted crops, which need a Winter chill in order to flower, typically bloom around April or so in most locations. In Florida and California, this can occur from February to March.
The Spring planted varieties can begin blooming about 39 to 41 days from planting time. Flowering usually takes place during June or so for about a month. A small number of blossoms, usually around five, open daily per plant.
The pods or capsules contain several small, brownish-yellow or brownish-black seeds, about the size of poppy seeds. The lower pods develop first. The seeds typically contain around 20% protein, and 30 to 45% oil, depending on the variety and growing conditions.
Where Grown
In the U.S., much of the rapeseed is grown in Idaho, the Plains, the Pacific Northwest, Upper Midwest, and the Southeast, including Florida. The crop is also cultivated in Minnesota, Wisconsin, Missouri, North Dakota, Kansas, Oklahoma, Montana, Alabama, Virginia, Kentucky, and Tennessee. This is often grown as a niche or specialty crop, such as organic food for poultry and “farm-to-table” restaurants with the cooking oil being recycled for biofuels.
Growing Conditions for Rapeseed
These crops prefer cool, moist growing conditions and well drained, fertile soils. Adapted to most soil types except heavy clay, they do best in medium textured soils or silt loams. Generally a slightly acid to alkaline pH is suitable. Their adaptability to very acid soils seems unclear. The plants have some tolerance for salt.
Although the crop can grow at 32°F, the best growth occurs when the soil temperature is around 50° or so. The minimum temperature for germination is around 40°F. Intolerant of drought, the crop needs 11 to 18 inches of water during the growing season. Adequate moisture results in an increased yield.
Planting Rapeseed
There are different varieties for specific soil types, various regions, growing conditions, and planting times. Some are more tolerant of frost than others. Herbicide tolerant varieties are available.
This can be planted during the Spring or Fall, depending on the location. Generally, the soil is tilled to create a smooth, well-prepared surface in order to minimize weeds. Once these quick growing crops germinate, they can suppress weeds. The seeding rate varies according to the variety, location, soil type, planting time, and planting method. Generally, about three to five pounds of seeds or so are sown per acre.
For bee gardens, plant ½ ounce of seed per 100 foot row or about six to nine seeds per square foot. If broadcasting, use a rate of three ounces per 1000 square feet. For larger areas, standard agricultural equipment or a grain drill can be used. Seeds should be planted from ½ to an inch deep, depending on soil type. Germination occurs in four to ten days.
Fertilizer is normally applied at planting time based on growing conditions and soil test results. This can include nitrogen, phosphorus, potassium, and sulfur. Additional nitrogen is needed for Spring-planted crops in some locations.
Problems of Rapeseed
Aster yellows and blackleg occur in some areas. The most common disease is sclerotinia, also called stem rot or white mold, which typically appears in cool, moist areas after flowering has taken place. Disease resistant varieties are available.
Deer browse the plants. Insects are uncommon on the Winter crop. Flea beetles can sometimes strike as soon as the seedlings of the Spring-planted crop emerge. Diamondback moth caterpillars are most prevalent during dry weather. Cabbage moths, stink bugs, and lygus bugs can occur on the Spring-planted crop.
Rapeseeds can be grown organically. Conventionally grown fields are sometimes treated with pesticides, which can pose potential risks for bees.
Acreage, Harvest and Expected Seed Yield
Rapeseed acreage fluctuations are largely due to weather conditions and crop prices. The average is around 1.5 million acres, although this has been as high as 1.77 million at times.
Maturity time and yield are influenced by the variety, weather, location, growing conditions, planting time, and growing practices. Harvest usually occurs from 80 days to 125 or so from planting. Pods are ready to harvest when around 40 to 50 per cent of the seeds in exposed pods are reddish brown. The average yield per acre is around 1400 to 2500 pounds or so, although yields can be somewhat higher in the Southeast, particularly in Florida.
Species of Rapeseed in Cultivation
Various species of rapeseed are grown in North America and elsewhere. Some of these have also naturalized,
Bird rape (Brassica rapa or Brassica campestris)
Also known as turnip rape, the plant was introduced from Eurasia. This cool season annual, biennial, or perennial has long been cultivated. It has naturalized in all regions of the country. Bird rape occurs as a weed in cultivated fields. The oil, known as rape oil, is used for soap, fuel, and as a lubricant. The roots are edible.
This erect, slender plant is one to three feet or more in height. It is usually branched. The foliage is bright green. The stem leaves, three to six inches long, are soft. The prickly, toothed, lower leaves, reaching a foot in length, can be lightly bristled.
Bird rape blossoms emerge unevenly, beginning in April in most locations. This has slightly smaller flower petals than some species. The pods are up to 2½ inches long. This species yield lots of yellow pollen. The amount of honey differs from one location to another.
Indian mustard (Brassica juncea)
Originally native to Eurasia, this has been grown for centuries. Also known as brown mustard, the widely variable plants are sometimes grown for the edible leaves, which are used as a vegetable. This species has naturalized in all regions.
It typically occurs as a weed in cultivated fields. Indian mustard dislikes coarse textured soils. The plant adapts to drought, salt, and various pH levels. Unlike most rapeseeds, this one is suited to partial shade.
This erect, slender, very variable, much branched annual or perennial is two to four feet in height. The stem leaves, three to six inches in length, are soft and prickly. The basal leaves can be large – over a foot in length. The edges are scalloped or notched. The small, bright yellow blooms, 3/8-inch long, open on a sparse cluster. These can be seen from June through September. The pods reach 2½ inches in length.
Rape or turnip (Brassica napus)
This much branched annual or biennial of unknown origin was introduced from Eurasia. It has naturalized in all states except the Dakotas, Minnesota, Nebraska, Wyoming, Utah, Arizona, Texas, Florida, and Pennsylvania. Rape is typically found in waste ground.
The plant grows from two to five feet in height. The lower stems can be purple. Sometimes, the stalked, lower leaves are bristly. The light yellow blooms, ¾ inch wide, can open unevenly over a period of time, generally from May to June.
The pods are two to four inches long. One particular variety, Brassica napus var. oleifera, yields rape oil, which is grown for edible and industrial purposes. The seeds also serve as bird and poultry feed.
Pollination and Bee Value
There appears to be disagreement regarding pollination. Some say this is a requirement for rapeseed, while others consider it non-essential but beneficial in terms of higher yields and crops that ripen evenly. The May 2013 issue of Bee Culture published a study on insect-pollinated crops that listed canola and rapeseed. In Canada, Bayer and others use bees to pollinate canola grown for seed.
Normally, most rapeseed farmers in North America benefit from the presence of nearby hives rather than contracting for pollination services. Around two to three hives per acre are recommended.
Rapeseed flowers, which are rich sources of nectar and pollen, are sure to attract bees, which will travel for several miles to reach the blossoms. The flowering season can be extended by planting both Spring-planted and Fall-planted crops or by choosing varieties with different maturity dates. In some cases, the Summer-blooming crop can provide bee forage when little else is available.
To derive full benefit from the nectar and good quality pollen, strong colonies are needed. The crop has been a major nectar and pollen plant in some regions, including the Plains, Idaho, and Wisconsin.
In general, the nectar at the base of flowers is quite accessible to bees. Most desirable of all is that from two nectaries at the base of the short stamens for this nectar contains a higher sugar content than that elsewhere within the flower. Each trip, a bee can visit 300 rapeseed flowers. A blossom can provide two to four mg. of nectar daily.
The nectar flow is so heavy that colonies have been known to add 20 pounds or so per day, usually enough to fill two supers. Rapeseed has a moderate honey potential of 60 to 100 pounds or so per colony although this can vary somewhat, based on the plant species and variety.
Normally, this is a premium quality, opaque honey with a mild, delicate, pleasing flavor that can vary somewhat among the different species and varieties of rapeseed. In some cases, it has a wine-like flavor. These honeys are often mixed with stronger tasting ones. Usually non-dripping, the fine grained, smooth, firm textured honey is quite easy to spread.
The color, quality, and aroma are influenced by growing conditions. This is especially true for heavy soils, which sometimes yield a honey with a less pleasing aroma and flavor.
In general, the color is often white or water white. However, it can also be clear, whitish-gray, pale buff, cream colored, pale or bright yellow, golden, or light amber. This honey is unsuitable as a Winter food for bees as it can cause dysentery.
One important characteristic with regard to this honey is the fact that it crystallizes extremely quickly due to the high glucose content. It should be removed from the hive as soon as the blooming period ends.
Crystallization can occur within days or even 12 to 24 hours in some cases. It usually happens within a week. Stored frames can granulate within a month. However, the honey from certain canola varieties doesn’t crystallize quite as swiftly.
Connie Krochmal is a writer and beekeeper in Black Mountain, North Carolina.
Photo courtesy of U.S. Canola Association.
