How to grow strong spring cabbage seedlings? Key points of cold-frame seedling raising techniques
Cabbage (Brassica oleracea L.) is an annual or biennial herbaceous plant of the genus Brassica in the family Brassicaceae, and is one of our important vegetables. Apart from Chinese kale (gai lan), which originated in China, all the varieties of cabbage originated along the coast from the Mediterranean to the North Sea. As early as 4000~4500 years ago, the ancient Romans and ancient Greeks already cultivated it.
Morphological characteristics
A biennial or perennial herbaceous plant, about 60-150 cm tall. The lower leaves are large, lyrate-pinnately parted, up to 40 cm long, with colored veins and petioles; the terminal lobe is large, with a rounded apex, an oblique-cordate base, and wavy margins with fine rounded teeth; there are 3-5 pairs of terminal lobes, obovate; the upper leaves are oblong, entire, stem-clasping; all leaves are fleshy, hairless, and covered with a white waxy bloom.
The raceme reaches 30 cm or more in the fruiting stage; the flowers are pale yellow, 10-15 mm in diameter; the sepals are oblong, upright, 8-11 mm long; the petals are obovate, 15-20 mm long, with a rounded apex and a claw. The silique is cylindrical, 5-10 cm long; the beak is 5-10 mm long and seedless; the pedicel is about 2 cm long; the seeds are spherical, about 2 mm in diameter, grayish brown.
Key points of techniques for growing strong spring cabbage seedlings in a cold frame
1. Selection of the bed site
For an improved small cold frame, the bed site should be selected in a field that is sheltered from the wind and facing the sun, with convenient irrigation, fertile soil, and a previous crop that is not a Brassicaceae plant.
2. Facility materials
25-30 small bamboo poles 2 m long, or 12-14 bamboo poles 3 m long. 6-7 kg of 10# iron wire and 3-4 kg of 12# iron wire. 8-10 wooden stakes 50-60 cm long and 6-8 cm in diameter, and 3-5 wooden poles 2 m long and 6-8 cm in diameter. 50-75 kg of corn or sorghum stalks, and 0.5-1 kg of binding wire or binding rope.
3. Construction of the cold frame
1. Basic structure. An improved small cold frame consists of three parts: the frame, the covering, and an additional windbreak wall. The frame includes the wall frame, tension wires, arch rods, and wooden stakes. The covering is greenhouse film. The windbreak wall, also called a wind screen, is usually made by tying corn or sorghum stalks together and is set outside the north wall of the cold frame to block and slow the invasion of cold wind coming from the north.
2. Specifications. The small cold frame faces south with its back to the north. The north wall is 75-90 cm high, the south wall is 15-20 cm high, and the east and west gable walls gradually increase in height from south to north. The size of the cold frame varies with the planting area. For every 1 mu of field to be planted, a seedling bed area of 12-15 sq m is needed. Usually, building one small cold frame 8-10 m long from east to west and 2.5-3 m wide from north to south can raise quality strong seedlings for 2 mu of field. The windbreak wall is about 12 m long from east to west and 2 m high.
3. Construction. This mainly involves piling up earth walls. After the bed site is marked out, dig soil around the outside of the bed to build the walls, tramping firmly while building, so that the north wall is 60-70 cm higher than the south wall, and the east and west gable walls form a single slope, high in the north and low in the south. After the wall frame is built, cut and trim it into a relatively smooth wall surface, with a wall thickness of about 35 cm. Then level the ground. Finally, make the windbreak wall. The method is to first draw a line 1 m outside the north wall, with a length extending 2 m beyond the north wall, then dig 3-5 pits at equal distances along this line, plant 2 m long wooden poles in them, tie 2-3 runs of iron wire on the poles, and tie crop stalks to the iron wire to form the windbreak wall.
4. Fertilizing and making beds. Apply 500-700 kg of manure soil with high organic matter content into the bed, 10-15 kg of special vegetable fertilizer, or 1 kg of urea, 10 kg of superphosphate, and 5 kg of potassium sulfate. After fertilizing, rake the ground level so that soil and fertilizer are mixed evenly, then make the beds. For ease of management, generally 2 small beds can be made inside the cold frame.
5. Selection of good varieties. For spring cabbage cultivation, in order to bring it to market earlier and increase profits, early-maturing or mid-early-maturing varieties should be selected that have strong winter hardiness, tolerance to low temperature and weak light, resistance to premature bolting, good quality, and disease resistance. For example: Zhonggan No. 10, No. 11, No. 15, and No. 21, paired with foreign small varieties such as Tieqiu, Zanmei, and Qishi. The seeding rate per mu of field is 50-60 g.
6. Sowing. The suitable sowing period is mid to late December. It is appropriate that there be 10-15 days of emergence and growth after sowing before "Minor Cold." Before sowing, first water the seedling bed thoroughly, and after the water seeps down, refill and level the bed surface with nutrient soil, then sow. The sowing rate in the seedling bed is 3-4 g per sq m. The sowing rate should be strictly controlled to prevent the seedlings from becoming spindly and weak due to overcrowding. After sowing, cover with soil to a thickness of 0.5-0.7 cm.
7. Covering. First stretch 3-4 runs of 10# iron wire across the east and west walls at intervals of 0.7-0.8 m, tying both ends to the large ends of the wooden stakes and fastening them to the outside of the gable walls. Then use small bamboo poles to tie 12-14 arch rods onto the iron wire at intervals of 0.7-0.8 m. Finally, cover with greenhouse film. First open a ditch in front of the south wall, bury the front film edge in it and press it tight; the side on the north wall is used for ventilation and as an entrance and exit for labor during seedling bed management, so the film edge can be laid flat on the wall surface and pressed tight with bricks; for ventilation, stretch 5-6 runs of film-pressing lines over the film surface to prevent it from being opened by the wind.
8. Seedling bed management. Do not ventilate from after sowing until the first true leaf appears. After the first true leaf appears, begin ventilation, with the vent opening gradually increasing from small to large for hardening. During this period, keep the seedling bed temperature at 15-20°C during the day and 8-10°C at night. After that, depending on seedling condition, choose sunny midday to thin seedlings and pull weeds. Thinning mainly removes yellow, thin, weak, and small seedlings. The new seedling-raising method changes the past one-stage seedling raising without pricking out into two-stage cultivation through pricking out to achieve quality strong seedlings. Prepare the pricking-out bed one week before pricking out.
Requirements for the seedling bed: the soil should be fertile, loose, and level, and a soil treatment should be carried out once to sterilize and kill insects and increase the seedling survival rate. Three days before pricking out, appropriately lower the nighttime temperature of the seedling bed, then harden again to enhance adaptability. Pricking out is carried out when the seedlings have 3 true leaves. Choose fine weather and use the method of pricking out the larger seedlings. That is, select large seedlings from the seedling bed for transplanting, leaving the small seedlings to continue growing. When pulling seedlings, handle them gently, without damaging leaves or roots, and keep as much of the original soil as possible.
The method is: first open a furrow and water, then plant the seedlings and cover with soil. The plant and row spacing is 8 cm square. After finishing, cover with a small arch shelter, taking care to keep warm and prevent cold. Do not ventilate for 3 days; after 3 days, ventilate slightly as appropriate according to seedling condition for hardening. Keep the seedling bed temperature at 14-15°C during the day and 7-8°C at night. Implement full ventilation 10-15 days before planting to harden strong seedlings. First increase ventilation greatly to harden the seedlings for field environment adaptability for 5-7 days, then remove all coverings so the seedlings transition to an open-field environment. When the seedling age is 60-70 days and the seedlings meet the appearance standard of "thick stems with 6 leaves, thick leaves with green color, well-developed roots, and no pests or diseases," plant the strong seedlings.