A Detailed Explanation of Onion Planting Methods and Key Technical Points
The onion (scientific name: Allium cepa L.) is a perennial herbaceous plant of the genus Allium in the family Liliaceae. The bulb is thick and large, nearly spherical; papery to thinly leathery, with a thick, fleshy inner layer; the leaves are cylindrical, hollow, thickest below the middle, gradually narrowing upward, shorter than the scape; the scape is stout, up to 1 m tall; the umbel is spherical, bearing numerous densely clustered flowers; the pollen is white; the tepals have a green midvein, oblong-ovate; the filaments are equal in length; the ovary is nearly spherical, with a nectary pit with a curtain at the base of the ventral suture; it flowers and fruits from May to July.
Growing Conditions for Onions
1. Temperature: Onions are highly adaptable to temperature. Seeds and bulbs can germinate slowly at 3-5°C. The optimum temperature for seedling growth is 12-20°C. Vigorous seedlings can tolerate low temperatures of -6 to -7°C. Bulb enlargement requires relatively high temperatures, but excessively high temperatures cause growth to decline and the plant to enter dormancy.
2. Light: Onions are long-day crops. During the bulb enlargement stage and the bolting and flowering stage, they need long-day conditions of more than 14 hours to grow normally. Under high-temperature and short-day conditions, they will only grow leaves without forming bulbs. The suitable light intensity is 20,000-40,000 lux.
3. Water: Onions should be supplied with sufficient water during the germination stage, the vigorous seedling growth stage, and the bulb enlargement stage. However, during the seedling stage and before overwintering, water must be controlled to prevent excessive seedling growth and frost damage. They are drought-tolerant and suited to 60-70% humidity; excessively high air humidity makes them prone to disease.
4. Soil: Onions are highly adaptable to soil, with fertile, loose, well-aerated neutral loam being preferable. Sandy loam easily achieves high yields, but clay loam produces solid bulbs with good color that store well. Onion roots have weak fertilizer-absorbing capacity, so high yields require sufficient nutrient conditions.
Seedling-Raising Techniques for Onions
1. Sowing time: Choosing a suitable sowing period is the key to raising strong onion seedlings. Sowing too early produces large seedlings that tend to bolt after overwintering; sowing too late produces weak, small seedlings with poor cold resistance and small bulbs and low yields. Taking the Huang-Huai River basin as an example, the best sowing period is early to mid-September.
2. Sowing quantity: Under normal conditions, the sowing rate for onion seedling beds is 4-5 kg per mu. Taking into account the need to cull and thin out 20% weak and inferior seedlings, the cultivation area should be 15 times that of the sowing seedbed. If the germination rate is below 70%, the sowing rate should be increased accordingly.
3. Bed preparation and fertilization: The bed height is 1.4-1.5 m and the bed width is 27 cm. After leveling the bed surface, apply 15 kg of superphosphate per mu and 4 cubic meters of well-rotted organic farmyard manure per mu as base fertilizer. After emergence, spread quick-acting nitrogen fertilizer in combination with watering, applying 10 kg of urea per mu.
4. Sowing method: After leveling the bed surface, water first, then broadcast evenly. Then cover with 0.8 cm of nutrient soil to ensure uniform emergence. If after sowing the soil moisture cannot meet the requirements for emergence, water with a watering can to promote emergence; sowing after sprouting is also possible.
5. Emergence management: After onion emergence, attention must be paid to the prevention and control of mildew and damping-off. The method is to use 150 g of 50% carbendazim or 40% chlorothalonil per mu, mixed with 30-40 kg of water for uniform spraying.
Field Management of Onions
1. Watering: About 20 days after transplanting, onions enter the seedling-recovery stage. At this time, large amounts of water must not be applied; overwatering lowers soil temperature and slows seedling recovery. At the same time, the newly transplanted seedlings have not yet sprouted new roots, so they cannot lack water. During this stage, onions should be watered frequently but in small amounts each time. The principle is not to let the seedlings wilt and not to let the ground dry out, so as to promote rapid rooting and survival of the seedlings.
2. Fertilization: Onions require 13-15 kg of nitrogen, 8-10 kg of phosphorus, and 10-12 kg of potassium per mu. Excessive nitrogen fertilizer must be avoided. For spring-sown onions, the soil should be kept moist before and after seedling emergence, with frequent watering and frequent cultivation. During the vigorous leaf growth stage and the bulb enlargement stage, fertilizer and water should be applied in a timely manner, with 15 kg of diammonium phosphate, 20 kg of diammonium phosphate, and 3-5 kg of potassium sulfate applied as topdressing per mu respectively.
3. Loosening the soil: Loosening the soil benefits both the development of the onion root system and the enlargement of the bulb. Generally, it should be done 3-4 times during the seedling stage, after each watering, and 2-3 times during the stem and leaf growth period. Once the plants close the rows, cultivation should be stopped. The cultivation depth should be about 3 cm, shallow near the transplanted plants and deep away from the plants.
4. Removing bolting stalks: For onions that bolt early, before the flower head forms, cut it off from the lower part of the flower bud, or split it from the tip of the flower stalk and tear it into two strips from top to bottom, to prevent flowering from consuming nutrients and to promote the growth of lateral buds, forming fuller bulbs. At the same time, spray Diguo Zhuangtiling in a timely manner. Practice has shown that for plants that have bolted early, a certain yield can still be obtained after taking measures to remove the bolting stalks.