Rutabaga is a well-known root vegetable in many countries. All parts of the plant are edible, but the fleshy root is commonly cooked and enjoyed in a variety of ways. Baked, steamed, mashed, and boiled are just a few of the ways to enjoy rutabagas. This vegetable is a filling and gives substance to soups and stews, or provides a hearty side dish.
| Common name | Oilseed rape, Rapeseed, Summer rape, Turnip Rape |
| Botanical name | Brassica napus (Oleifera Group) |
| Family | Brassicaceae |
| Species | napus |
| Life cycle | Annual |
| Plant type | Annual |
| Sunlight | Full Sun |
| Soil condition | High Organic Matter |
| Soil ph | Neutral |
| Drainage | Well-Drained |
| Harvest time | Fall |
| Flowering period | Fall |
| Height | 2 ft. – 4 ft. |
| Width | 2 ft. – 4 ft. |
| Flower color | Gold, Yellow |
| Leaf color | Green |
| Stem color | Green |
| Fruit type | Siliqua |
| Uses | Naturalized Area |
I. Appearance and Characteristics
Rapeseed (Brassica napus subsp. napus), also known as oilseed rape, is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed, which naturally contains appreciable amounts of erucic acid. The term “canola” denotes a group of rapeseed cultivars that were bred to have very low levels of erucic acid and which are especially prized for use as human and animal food. Rapeseed is the third-largest source of vegetable oil and the second-largest source of protein meal in the world.
Brassica napus grows to 100 centimetres (39 inches) in height with hairless, fleshy, pinnatifid and glaucous lower leaves which are stalked whereas the upper leaves have no petioles.
Rapeseed flowers are bright yellow and about 17 millimetres (3⁄4 in) across. They are radial and consist of four petals in a typical cross-form, alternating with four sepals. They have indeterminate racemose flowering starting at the lowest bud and growing upward in the following days. The flowers have two lateral stamens with short filaments, and four median stamens with longer filaments whose anthers split away from the flower’s center upon flowering.
The rapeseed pods are green and elongated siliquae during development that eventually ripen to brown. They grow on pedicels 1 to 3 cm (3⁄8 to 1+3⁄16 in) long, and can range from 5 to 10 cm (2 to 4 in) in length. Each pod has two compartments separated by an inner central wall within which a row of seeds develops. The seeds are round and have a diameter of 1.5 to 3 mm (1⁄16 to 1⁄8 in). They have a reticulate surface texture, and are black and hard at maturity.
Rapeseed oil is predominantly cultivated in its winter form in most of Europe and Asia due to the requirement of vernalization to start the process of flowering. It is sown in autumn and remains in a leaf rosette on the soil surface during the winter. The plant grows a long vertical stem in the next spring followed by lateral branch development. It generally flowers in late spring with the process of pod development and ripening occurring over a period of 6–8 weeks until midsummer.
II. How to Grow and Care
Sunlight
Like most plants, rutabaga must be spaced adequately to ensure each plant receives enough sunlight on all above ground plant plants and to ensure that disease is unable to take hold. The majority of Brassicaceae will thrive in around 6 hours of direct sunlight each day. The plants should be positioned in full sun though care should be taken to ensure that they are protected from wind.
Watering
Rutabaga requires plenty of water to develop and grow. When propagating, potted seedlings should be stood in water to ensure that compost is sufficiently moist before planting to ensure that roots establish quickly. Once planted surrounding soil should be watered well, and watered regularly whilst the plants establish themselves and throughout their growth.
Soil
Rutabaga grows best in firm, fertile and naturally-draining soils. Areas to be planted should be dug over in the preceding fall, with stones removed and well-decomposed manure or compost worked in ready for the growing season. Growers can also tread on the soil area to ensure that air pockets have been removed and the surface made adequately firm. In terms of pH, all families of Brassica grow best in soils just below neutral at 6-7 except for collards and mustards which enjoy slightly more acidic soils and cabbages that will tolerate slightly alkaline soils up to a pH of 7.5.
Fertilizing
Apply ¼ cup per 10 feet of row of a nitrogen-based fertilizer (21-0-0) 6 weeks after emergence to encourage rapid plant growth. Place the fertilizer to the side of the plants and irrigate it into the soil.
Planting Instructions
Propagation of rutabaga seedlings is best started indoors with seeds planted six to four weeks before the last frost in spring or, for a winter crop ten to twelve weeks before the first frost in the fall. The seeds should be sown to a depth of a 1.3 cm. Once germinated, seedlings can be thinned to 8 cm between each plant. They can be transplanted once a height of 6 cm has been reached; for Brussels sprouts and kale, the height should be about double this. Spacing then depends on Brassicaceae but ranges from 30 to 76 cm.
Pruning
The large, thick low-lying leaves characteristic of many brassicas call for fairly regular maintenance and occasional pruning to ensure that leaves touching the ground do not start to rot. As well as removing possible sites for diseases to take hold, it helps to ensure that the plant’s energy is directed towards healthier growth. Any yellow, flat-looking leaves can simply be torn off or pruned with scissors. Large, healthy leaves covering other plants can also be removed but should be eaten.
Pests and Diseases
- Common Diseases
The main diseases of the winter rapeseed crop are canker, light leaf spot (Pyrenopeziza brassicae), alternaria- and sclerotinia- stem rots. Canker causes leaf spotting, and premature ripening and weakening of the stem during the autumn-winter (fall-winter) period. A conazole- or triazole- fungicide treatment is required in late autumn (fall) and in spring against canker while broad-spectrum fungicides are used during the spring-summer period for alternaria and sclerotinia control. Oilseed rape cannot be planted in close rotation with itself due to soil-borne diseases such as sclerotinia, verticillium wilt and clubroot.
Transgenic rapeseed shows great promise for disease resistance. Transexpression of a class II chitinase from barley (Hordeum vulgare) and a type I ribosome inactivating protein into B. juncea produces a large fungal resistance effect. Chhikara et al., 2012 finds that this combination of transgenes reduces hyphal growth by 44% and delays disease presentation in Alternaria brassicicola of juncea.
Blackleg (Leptosphaeria maculans/Phoma lingam) is a major disease. Yu et al., 2005 uses restriction fragment length polymorphism analysis on two doubled haploid populations DHP95 and DHP96. They find one resistance genes in each, LepR1 and LepR1.
- Common Pests
Rapeseed is attacked by a wide variety of insects, nematodes, slugs as well as wood pigeons. The brassica pod midge (Dasineura brassicae), cabbage seed weevil (Ceutorhynchus assimilis), cabbage stem weevil (Ceutorhynchus pallidactylus), cabbage stem flea beetle (Psylliodes chrysocephala), rape stem weevil (Ceutorhynchus napi) and pollen beetles are the primary insect pests that prey on the oilseed rape crop in Europe. The insect pests can feed on developing pods to lay eggs inside and eat the developing seeds, bore into the plant’s stem and feed on pollen, leaves and flowers. Synthetic pyrethroid insecticides are the main attack vector against insect pests though there is a large-scale use of prophylactic insecticides in many countries. Molluscicide pellets are used either before or after sowing of the rapeseed crop to protect against slugs.
III. Uses and Benefits
Rapeseed is grown for the production of edible vegetable oils, animal feed, and biodiesel. Rapeseed was the third-leading source of vegetable oil in the world in 2000, after soybean and palm oil. It is the world’s second-leading source of protein meal after soybean.
- Vegetable oil
Rapeseed oil is one of the oldest known vegetable oils, but historically was used in limited quantities due to high levels of erucic acid, which is damaging to cardiac muscle of animals, and glucosinolates, which made it less nutritious in animal feed. Rapeseed oil can contain up to 54% erucic acid. Food-grade oil derived from rapeseed cultivars, known as canola oil or low-erucic-acid rapeseed oil (LEAR oil), has been generally recognized as safe by the United States Food and Drug Administration. Canola oil is limited by government regulation to a maximum of 2% erucic acid by weight in the US and 2% in the EU, with special regulations for infant food. These low levels of erucic acid are not believed to cause harm in human infants.
- Animal feed
Processing of rapeseed for oil production produces rapeseed meal as a byproduct. The byproduct is a high-protein animal feed, competitive with soybean. Rapeseed is an excellent silage crop (fermented and stored in air-tight conditions for later use as a winterfeed). The feed is employed mostly for cattle feeding, but is also used for pigs and poultry. However, the high levels of erucic acid and glucosinolates in natural rapeseed oil significantly lowers the nutritional value of rapeseed press cakes for animal feed. In China, rapeseed meal is mostly used as a soil fertilizer rather than for animal feed.
- Biodiesel
Rapeseed oil is used as diesel fuel, either as biodiesel, straight in heated fuel systems, or blended with petroleum distillates for powering motor vehicles. Biodiesel may be used in pure form in newer engines without engine damage and is frequently combined with fossil-fuel diesel in ratios varying from 2% to 20% biodiesel. Owing to the costs of growing, crushing, and refining rapeseed biodiesel, rapeseed-derived biodiesel from new oil costs more to produce than standard diesel fuel, so diesel fuels are commonly made from the used oil. Rapeseed oil is the preferred oil stock for biodiesel production in most of Europe, accounting for about 80% of the feedstock, partly because rapeseed produces more oil per unit of land area compared to other oil sources, such as soybeans, but primarily because canola oil has a significantly lower gel point than most other vegetable oils.
Because of the changes to the environment caused by climate change, a 2018 study predicted that rapeseed would become an unreliable source of oil for biofuels.
- Other uses
Rapeseed is also used as a cover crop in the US during the winter as it prevents soil erosion, produces large amounts of biomass, suppresses weeds and can improve soil tilth with its root system. Some cultivars of rapeseed are also used as annual forage and are ready for grazing livestock 80 to 90 days after planting.
Rapeseed has a high melliferous potential (produces substances that can be collected by insects) and is a main forage crop for honeybees. Monofloral rapeseed honey has a whitish or milky yellow color, peppery taste and, due to its fast crystallization time, a soft-solid texture. It crystallizes within 3 to 4 weeks and can ferment over time if stored improperly. The low fructose-to-glucose ratio in monofloral rapeseed honey causes it to quickly granulate in the honeycomb, forcing beekeepers to extract the honey within 24 hours of it being capped.
As a biolubricant, rapeseed has possible uses for bio-medical applications (e.g., lubricants for artificial joints) and the use of personal lubricant for sexual purposes. Biolubricant containing 70% or more canola/rapeseed oil has replaced petroleum-based chainsaw oil in Austria although it is typically more expensive.
Rapeseed has been researched as a means of containing radionuclides that contaminated the soil after the Chernobyl disaster as it has a rate of uptake up to three times more than other grains, and only about 3 to 6% of the radionuclides go into the oilseeds.
Rapeseed meal can be incorporated into the soil as a biofumigant. It suppresses such fungal crop pathogens as Rhizoctonia solani and Pratylenchus penetr.
IV. Harvesting and Storage
Harvesting of brassicas depends on family and variety. Summer cabbages cauliflower kohl and common broccoli can all be harvested from the end of summer whilst many others are good for picking in the fall or winter. Low growing brassicas such as cabbages should be harvested by cutting close to the ground level using a sharp knife. When harvesting cabbages the whole plant should be lifted to reduce the risk of club root. Broccoli should be harvested when flower shoots are well formed. Kale on the other hand can be harvested throughout the season on a frequent basis.
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