Even if the cultivation of rapeseed is not worthwhile for hobby gardeners in terms of harvest, it can still be used as green manure. We explain how to do this.
Rapeseed (Brassica napus) is only known to most people in the form of rapeseed oil or as the yellow flowers in the fields in spring. However, very few people know that rapeseed can also be interesting for growing in your own garden. Although the effort to grow rapeseed for harvesting is too high, it is wonderfully suitable as green manure in the garden. We will tell you the advantages of using rapeseed as green manure and how best to grow and care for rapeseed in your garden.
rapeseed
Rapeseed belongs to the cruciferous family (Brassicaceae), as does mustard (Sinapis arvensis) and many types of cabbage such as kale ( Brassica oleracea var. sabellica) or broccoli (Brassica oleracea var. italic ). We grow rapeseed as an oil crop. Rapeseed oil is considered very he althy due to its high proportion of unsaturated fatty acids and its low cholesterol content. We all enjoy rape the most in spring, when entire areas of the country are bathed in the bright yellow of the rape blossom. Even if the cultivation of rapeseed is of great importance in agriculture, it is hardly worthwhile to cultivate it in your own garden. The yields are too low and the effort involved in actually extracting oil from your own rapeseed is too high. The cultivation of rapeseed in the garden is much more worthwhile as green manure. Check out our article on how best to integrate it into your garden.
Rapeseed: origin and characteristics
Rapeseed is a cross between turnip rape (Brassica rapa) and wild cabbage (Brassica oleracea). Because of its high oil content, it has been valued and cultivated for centuries. It is said that the Romans already cultivated rapeseed. Originally, rapeseed probably comes from the eastern Mediterranean region and was cultivated for the production of cooking oil and lamp oil. From the 17th century, the cultivation of rapeseed increased more and more as the demand for lamp oil increased. At that time, rapeseed, together with the closely related turnip rape, became the most important oil crop in Germany.
Rapeseed is an annual or biennial herbaceous plant with an upright, branched stem. It can reach a height of 30 to 150 centimeters. Canola flowers are bright yellow and the flowers can be either self-pollinated or insect-pollinated. Pods develop from the flowers, in which 12 to 20 seeds form. The dark brown to black seeds are round and have a diameter of 1.5 to 2.5 millimeters. Rape seeds can contain up to 40% oil. The rapeseed oil is extracted from them after the harvest.
Rapeseed varieties
In the case of commercially grown rapeseed, the oil composition and the oil yield of the seeds are of particular importance when selecting the variety. When cultivating rapeseed as green manure, however, the oil content is negligible. A distinction is made here between winter and summer varieties. Winter oilseed rape has the advantage that it stays on the bed throughout the winter, so the soil is covered. This prevents erosion, for example. Winter oilseed rape is particularly suitable as green manure, since few vegetables are grown in the garden in the cold season anyway and the beds usually lie fallow. Summer rape is sown in spring. If you want to use the bed for growing vegetables in summer, the rapeseed only has a short time to develop, but summer rapeseed as green manure will also have positive effects. Whether you decide to use winter or summer rape as green manure depends on your personal cultivation planning and crop rotation. Depending on when the rapeseed fits on your bed, it will be planted.
If you have decided on summer rapeseed, we can recommend the following varieties: 'Petranova', 'Fura', 'Evita', 'Lisonne', 'Star'.
The following winter oilseed rape varieties include: 'Attila', 'Akela', 'Bishop', 'Bristol', 'Edita'.
Buy rapeseed: You should pay attention to this
When buying rapeseed, you should pay particular attention to the variety. Depending on whether you want to grow your green manure in summer or winter, summer or winter rape varieties are suitable. You can find oilseed rape seed in garden centers, nurseries or on the Internet.
Grow rapeseed as green manure
Green manure refers to the cultivation of plants that contribute to improving the soil, the nutrient balance, the soil structure and the water balance in the soil. The green manure is grown before or after the actual crop and is not harvested butincorporated into the ground, or left in to freeze. The nutrients therefore remain on the field or bed and are not removed.
Advantages of oilseed rape as green manure
Cultivating rapeseed as green manure has many advantages: the deep taproots of rapeseed loosen the soil and counteract compaction. In addition, the good rooting of the plant improves the soil structure and thus also the water retention capacity and the aeration of the soil. Because the organic substance of the rape remains on the bed and is not removed, the soil is enriched with humus. This improves soil fertility and promotes soil life. With the remaining parts of the plant, nutrients are also introduced into the soil by the oilseed rape - above all sulphur, nitrogen and potassium. Finally, the cultivation of rapeseed as green manure also ensures that the soil is covered. This protects the soil from drying out and from erosion.
Read more exciting facts and interesting facts about the benefits of green manure here.
When is rape used as green manure?
Rapeseed can be grown either as a previous crop or as a subsequent crop for the planned crop. In addition, oilseed rape can be cultivated as a winter or summer crop. So when you grow canola as cover crops in your garden depends entirely on your preferences and plans. As a rule of thumb, use oilseed rape only as a cover crop for plants from a plant family other than cruciferous.
The right time to sow is of course different for summer and winter oilseed rape: Summer oilseed rape should be sown as early as possible so that it can develop sufficiently. Summer oilseed rape is best sown between the beginning and middle of March. Winter rape should be sown in the second half of August, and you should have sown your rape by the beginning of September at the latest. Rapeseed is frost tolerant down to -20 °C.
Tip: Rapeseed should never be used as green manure if other cruciferous plants, such as cabbage varieties such as cauliflower (Brassica oleraceavar. botrytis) or radishes (Raphanus sativus var. sativus), or are to be cultivated. Otherwise diseases such as clubroot may occur.
Procedure when growing oilseed rape as green manure
Rapeseed can be sown directly into the bed, you don't have to pull it ahead. Prepare for thisprepare the seedbed so that it is free of weeds and finely crumbly. Rapeseed needs deep soil and a pH of 6.5. Once the seedbed has been prepared, the grains are placed at a depth of one to two centimeters with a row spacing of 13 centimetres. The seed density for spring rape is 100 to 120 grains per square meter. With winter oilseed rape, you only need 60 to 90 grains of seed for this area. After sowing, the grains are lightly covered with soil and watered.
Summary of growing oilseed rape as green manure:
- Deep Ground
- pH value: 6.5
- Fine crumbly and weed-free seedbed
- Sowing depth: 1 - 2 cm
- Row spacing 13 cm
- Seed density: 100 - 120 grains/sqm for summer rape; 60 - 90 grains/sqm for winter oilseed rape
- Cover seeds lightly with soil
- Cast on
Cultivate oilseed rape
Your rape needs sufficient moisture, especially after sowing. If it doesn't rain enough, you should water your rape regularly. The same applies to the hot summer months. Winter oilseed rape no longer needs to be watered as soon as it gets cooler and rains more often. Before the rows close, i.e. before the rows are completely overgrown with rape, you should also regularly remove the weeds and rake in the rows. This fights unwanted weeds and grasses and loosens the soil. In order for the oil-rich rapeseed grains to develop properly, the heavy feeder rapeseed must be sufficiently fertilized. Since the oil yield is not important when cultivating rapeseed as green manure, fertilization is superfluous. Rather, the rape itself should serve as fertilizer and nutrient supplier for the next crop.
Harvest rapeseed and use as green manure
Rapeseed as green manure is not harvested, but worked into the soil. In the case of winter oilseed rape, this is the case in spring. If summer rape has been sown as early as possible, it can be dug up in early summer. However, the rapeseed should definitely be dug up before seeds have formed. Before you work the rape into the soil, you should remove all unwanted weeds so that they do not remain on the bed. Next, chop up the plants with a sharp spade. Then the crushed plant parts are mixed with a digging fork or hands. Finally, dig up the entire bed on which the green manure stood, approximatelyspade deep. In this way, the rape is worked well into the soil. Now you should let the area rest for at least a week before you replant it. This gives the green manure sufficient time to rot in the soil.
If you are looking for other interesting plants besides oilseed rape that make good groundcover, here are 10 hardy groundcover plants.