1, seeds can germinate normally only after low temperature treatment, such as lettuce seeds, garlic seeds and celery seeds. Second, the environment is too dry to keep the seeds moist all the time, and it is difficult to germinate normally; Third, the concentration of chemical fertilizers and pesticides applied in the seedbed is too high, which makes the seeds lose their germination ability. The solution is: (1) Select high-quality fresh seeds from reliable seed suppliers. Pay attention to the production date, expiration date and storage method on the packaging bag. (2) Adopting the correct method of accelerating germination. If low temperature (treatment) is needed to accelerate germination, it must be refrigerated and treated at low temperature. In the case of high temperature, we should pay attention to cooling and moisturizing, such as setting up shade shed, covering shade net, covering straw and watering well water. At the same time, high concentration of human and animal manure and chemical fertilizer should be avoided in the seedbed.

2. Improper soil coverage. Too thick, too thick, too thin and too dry soil in seedbed all affect the normal growth of seedlings. Too thick plastic film is easy to lead to late emergence, crooked seedlings and small old seedlings; If it is too thin and dry, it is easy to cover seedlings, expose seedlings and climb seedlings. After sowing, the soil cover of seedbed is generally required to be 1.5 ~ 2 cm thick; Large seeds should be covered with 2 ~ 3 cm thick soil, and the seedbed should be watered before sowing, and the seedbed should be kept moist before and after emergence.

3. The seedlings didn't get timely exercise. Exercise too early and for too long after emergence, which is easy to burn or even kill seedlings. If the seedling is tempered too late and the time is too short, it is easy to have long seedlings and thin seedlings. The correct method is: after 80% of the seeds emerge, uncover the plastic film in time, set up a shade shed, and harden the seedlings every morning before 10 and afternoon 16 for 2 hours each time. After the first real leaf appears, gradually increase the hardening time, achieve good tempering but not too much, and pay attention to prevent strong wind from blowing directly and strong sunlight from drying for a long time. One week before transplanting, remove the shade shed and naturally temper the seedlings.

4. Fertilizer and water management to prevent seedlings from growing white. (1) fertilization. The application of immature organic fertilizer in seedbed is easy to burn roots and die seedlings; Excessive topdressing after emergence is too thick, and excessive drought is easy to burn seedlings. Note that the ratio of organic fertilizer to seedbed soil is generally 1: 1. Generally, it is not advisable to topdress before two real leaves, and dilute manure or dilute biogas slurry can be sprayed after 16 pm. Generally, try not to use chemical fertilizer for topdressing. (2) It is best to keep the seedbed moist. If it is dry at high temperature, water should be poured once every morning before 10 and once every afternoon after 16, but it is not advisable to water too much each time. If it rains for a long time, pay attention to ditch and drain around the seedbed. If possible, you can set up a canopy, and you can use a cover to ventilate and dehumidify in sunny days. (3) In summer, seedlings have high temperature and fast growth, and they are easy to grow white. It is necessary to divide or space seedlings in time to increase the nutritional area and growth space of seedlings. In case of overgrowth of seedlings, 40-50% chlormequat chloride 1000 times solution can be sprayed to control overgrowth of seedlings and achieve the purpose of thick stems and green leaves.

5. All the pests and diseases are dead. Diseases and insect pests and virus diseases are serious in high temperature season, so it is necessary to do a good job in pest control in time, check pests frequently, nip in the bud, and achieve early treatment, minor treatment and cure. In particular, aphids not only directly harm plants, but also spread viral diseases. The specific pest control measures are (1) diseases. The common diseases of seedbed include damping-off disease, anthracnose, damping-off disease and epidemic disease. Common pesticides are 25% metalaxyl wettable powder 800 times, or 50% carbendazim wettable powder 1000 times, or 70% thiophanate-methyl 1000 times, and 86.2% Tongling 1400 times. (2) pests. The common pests in seedling stage are black cutworm, earthworm and cricket. Black cutworms can be captured or controlled by chemicals, and the capture can be carried out at dawn or evening. The pesticide can be made into toxic soil by adding 0.75 ~ 1 kg fine soil to 0.5% diazinon granules per mu, and then it can be sprinkled in Miao Di, or it can be sprayed in Miao Di with 48% Robben solution which is 0/000 times of/kloc-0 in the evening.

6. Prevent heavy rain and drought. (1) Strong convective weather such as thunderstorm and rainstorm often occurs in summer. The erosion of heavy rain is easy to harden the soil and flood the seedbed, which is not conducive to the emergence of seeds. The seedbed should be built in high dry land with smooth drainage around it. When the rainstorm comes, temporary coverage should be taken to reduce the harm of the rainstorm. If the seeds are not unearthed due to heavy rain after sowing, shallow intertillage should be carried out on the seedbed after rain to prevent the soil surface from hardening. (2) drought prevention. In summer, the sunshine is strong, and the water on the soil surface evaporates quickly, which is easy to cause water shortage in the seedbed. Therefore, when sowing the seedbed, water the soles of the feet, once in the morning and once in the evening, or use sunshade nets and grass curtains to shade the sun at noon to reduce water evaporation.