Key technical points for seedling management of early spring stubble vegetables during Minor Cold
January 5 is the Minor Cold solar term, falling around the "Sanjiu" period and marking the start of the coldest days of the year. At this time, the average temperature in the Beijing area is around -5°C, the extreme minimum temperature is below -15°C, and there are many hazy days; it is the period of the year with the shortest sunshine hours, the lowest temperatures and highly changeable weather. It is the critical period for raising seedlings of warm-loving vegetables such as peppers, eggplants, tomatoes and other solanaceous fruits and cucurbits for early spring stubble in greenhouses, plastic tunnels and small arched tunnels, and it is also the critical period for managing overwintering stubble vegetables in greenhouses.
? Seedling raising and management of early spring stubble crops
Cultivating age-appropriate strong seedlings is very important; strong seedlings are the foundation of high quality and high yield, as the saying goes, "strong seedlings mean half the harvest." During this period, temperatures are low, light is weak and sunshine hours are short, so raising temperature, retaining heat and increasing light are the keys to successful seedling raising. Seedling-raising sheds should be chosen as solar greenhouses with good lighting conditions and good heat retention, and heating wires should be laid before seedling raising; if conditions permit, supplemental lighting lamps can be installed.
◆Seedling raising of cucurbits and spring tunnel solanaceous vegetables Seedling raising has begun for warm-loving crops such as early spring stubble greenhouse cucumbers and zucchini, and spring tunnel-planted tomatoes, eggplants and peppers. For cucumbers, tomatoes and eggplants, grafting should be used as much as possible, which can enhance cold resistance, disease resistance and stress resistance, and also has a nematode-resistant effect. Generally, tomato seedlings are 50-60 days old, eggplant seedlings 60-70 days, and cucumber seedlings 40-50 days. Tomatoes and eggplants are raised in 50-cell or 72-cell plug trays; cucumbers are raised in 32-cell or 50-cell plug trays, or in 8×8 cm nutrient pots. Use branded, high-quality seedling substrate, or prepare your own substrate with a 2:1 ratio of peat nutrient soil and vermiculite, adding 10 kg of nitrogen-phosphorus-potassium compound fertilizer per cubic meter. Do a good job of seed soaking, germination and chemical treatment, sow on sunny days, and ensure uniform sowing and consistent soil covering depth.
◆Seedling raising of cabbage and lettuce The best seedling-raising period for early spring open-field plastic film mulching cultivation of cauliflower, cabbage, celtuce and lettuce is in mid-January. Use 72-cell or 128-cell plastic plug trays for seedling raising, choose early-maturing, good-quality varieties such as "Zhonggan 21", sun the seeds for one day in advance, water thoroughly to build up bottom moisture, and then sow evenly. Remember that the night temperature for cabbage-type seedlings should not remain below 12°C for a long time, so as to avoid passing through the vernalization stage too early and bolting prematurely.
◆Management of already-raised seedlings Early spring stubble greenhouse tomatoes, peppers, eggplants and other solanaceous crops, as well as cabbage, celery, lettuce and other growing seedlings, are in an important management period. First, do a good job of heat preservation and let them see more light; turn on supplemental lighting lamps on consecutive cloudy days for about 12 hours of supplemental light per day; also note that the night temperature must not be too low, and must be kept at least above 13°C, otherwise long-term low temperatures will affect flower bud differentiation, form deformed fruits, and directly affect the quality and yield of later fruits. For ordinary seedbed seedling raising, prick out seedlings in time at the 2-leaf stage, and at the same time do a good job of disease control during the seedling stage. Recently, many sheds have had mole damage, which should be controlled by means such as mole traps.
? Harvesting and vine pulling of autumn-winter stubble crops in solar greenhouses
Autumn-winter stubble warm-loving crops such as tomatoes, cucumbers, peppers, zucchini and eggplants have entered the late growth stage. Decide whether to pull the vines according to plant growth and the temperature inside the greenhouse. If the minimum nighttime temperature inside can be above 13°C and the plants are growing robustly, delay vine pulling as much as possible. If these conditions cannot be met, pull the vines at the proper time, and promptly clear the stubble and prepare the soil for sowing or transplanting fast-maturing vegetables with good cold tolerance such as rapeseed and lettuce.
? Critical period for managing overwintering stubble warm-loving vegetables
Currently it is the critical period for managing overwintering stubble warm-loving vegetables such as tomatoes and cucumbers. Pay attention to weather changes to prevent strong cold waves and consecutive cloudy days from damaging crops, and take temporary heating measures when necessary, such as heat lamps, heating combustion blocks or electric hot-air furnaces. Frequently wipe and clean the greenhouse film to enhance light transmittance; promptly prune branches and remove side shoots, lower vines and pinch tips, assist pollination, and thin out excess flower buds and fruits; water and topdress scientifically. Topdressing should preferably use fully nutritious, reasonably proportioned quick-dissolving fertilizers such as "Christmas Tree" applied with drip irrigation, or apply seaweed acid or humic acid organic liquid fertilizers complete in nitrogen, phosphorus and potassium with the water; set up water storage tanks, jars or barrels in the greenhouse and water after the water temperature rises, and also note that small amounts of frequent watering are preferable. In winter, vegetables in greenhouses should avoid flood irrigation to prevent a sudden drop in soil temperature from affecting root growth and the ability to absorb water and nutrients.
???? Transplanting and sowing of cold-tolerant fast-maturing vegetables in greenhouses
It is the season for sowing and transplanting fast-maturing vegetables grown in solar greenhouses, such as rapeseed, garland chrysanthemum, spinach, lettuce, bok choy and cherry radish. Apply 1500-2000 kg of fully decomposed, finely crushed organic fertilizer, prepare the soil carefully, and make the ground level, the beds level and the ridges straight, with the surface soil loose and free of visible or hidden clods. Garland chrysanthemum, spinach, cherry radish and bok choy are suitable for direct sowing; after watering thoroughly to build up bottom moisture, sow evenly, cover with soil to a consistent thickness, and after sowing cover with a layer of plastic film, which can retain heat and moisture, and remove it promptly when 50% of seedlings have emerged. Strengthen management during the growth period, and produce fresh, tender and safe products to supply the spring off-season market.
? Management under special weather
■Snowy days Clear snow from the front roof and rear roof in time during snowfall. Avoid snow melting on straw mats or thermal insulation quilts and reducing their heat retention effect. After snowfall stops and on cloudy days, on the premise of ensuring the greenhouse temperature is above 12°C, uncover the straw mats around noon so that crops receive 2 hours of scattered light; in weather that turns clear after long cloudy days, uncover the straw mats one every other one, or roll up half of the thermal insulation quilt, to prevent overly strong sunlight from causing plant wilting; on snowy and cloudy days, do not carry out farming operations such as topdressing, watering, pruning or fruit thinning. For some greenhouses with large spans and relatively poor frame stability, support and reinforce the frames in time to prevent the shed from collapsing during snowfall.
■Extremely cold weather To ensure the safe production of warm-loving vegetables, temporary heating measures can be taken, such as installing heat lamp conversion bulbs, air heating wires, electric hot-air furnaces, heating combustion blocks and oil-fired hot-air furnaces, to avoid excessively low indoor temperatures affecting crop growth and causing freeze damage.
■Consecutive cloudy days and hazy days Consecutive cloudy days and hazy weather can have a relatively large adverse impact on the solar greenhouse environment, easily causing weakened light, lower temperatures and increased humidity in the greenhouse, while weak light, low temperature and low humidity are also among the main causes of high incidences of diseases and pests in greenhouse vegetables. Therefore, adopting measures such as supplemental lighting, dehumidification and heating during consecutive cloudy or hazy weather is an important part of ensuring the healthy growth of winter greenhouse vegetables.