What are the precautions for delayed vegetable seedling raising in autumn?

How can delayed autumn vegetable seedlings recover quickly, suffer fewer dead plants, grow strong, and bear more fruit? These are questions greenhouse growers care about greatly. So what are the precautions for delayed vegetable seedling raising in autumn?

1. Determine the seedling raising time

Broccoli for market around the Spring Festival should be chosen from mid-to-late maturing varieties, and the seedling raising time should be from the end of August to the first ten days of September; red-skinned lettuce for market around the Spring Festival should be raised in greenhouses in mid-September; early-maturing red rape moss should be raised in mid-August, and mid-to-late maturing red rape moss should be raised from the end of August to the first ten days of September.

2. Prepare the seedbed

For plug tray substrate seedling raising, the seedbed should be chosen in a place with higher terrain, convenient drainage and irrigation, and a water source. The seedbed surface should be level to ensure the plug trays sit steadily without air gaps; for conventional seedling raising, choose a field with higher terrain, convenient drainage and irrigation, and higher organic matter content. The seedbed border should be 1.2 m wide, and the ditch should be 30×20 cm wide and deep. Prepare cooling facilities for seedling raising such as shade nets and bamboo arches.

3. Seed treatment

Sun-dry the seeds and soak them in warm water. Sun-drying: at noon, place the seeds on a bamboo tray or newspaper and sun them for about 2 hours to kill part of the harmful microorganisms on the seed surface and break seed dormancy. Warm water soaking: soak the seeds in 55°C warm water for 15 minutes, stirring the seeds continuously while soaking. After soaking, repeatedly rub and wash the seeds with clean water to remove the mucus on the seed surface. You can also soak the seeds in boric acid, manganese sulfate, and zinc sulfate (200 mg/L) for 5-6 hours, which has a good early-maturing and yield-increasing effect on vegetables.

4. Germination and sowing

For germinated seeds, when the sprout is about 0.5 cm long, that is, the so-called “white break” stage, they can be sown. The thickness of the covering soil is crucial. If the covering soil is too thick, it is not easy for seedlings to emerge; if the covering soil is too shallow, the seedlings are likely to “wear hats” when emerging (the cotyledons are clamped by the seed shell). Generally, the depth of covering soil after sowing should be about 2 times the thickness of the seed. In addition, after sowing, keep the water content of the nutrient soil at 80%. For seeds that have not been germinated, the depth of covering soil should be about 3 times the thickness of the seed.

5. Cultivate strong seedlings

Manage flexibly according to seedling condition, weather, and seedbed soil moisture. Water in the evening of a sunny day or on a cloudy day, and water thoroughly in one go. If topdressing is needed, spray the seedlings with a solution of 0.3% potassium dihydrogen phosphate plus 0.2% urea in water. Insufficient light (too long shading), excessively high temperature, excessively high humidity, excessive nitrogen fertilizer, and too high sowing density can all easily cause seedling overgrowth. Increase ventilation and light duration, apply more phosphorus and potassium fertilizer, and transplant and set out seedlings in time. At the same time, spray 50% chlormequat at 2000-2500 times dilution to strengthen the seedlings.

6. Prevent pests and diseases well

Diseases at the seedling stage mainly include damping-off and Rhizoctonia rot in the early stage, and early blight, gray mold, and Fusarium wilt in the later stage. You can use 1-2 pesticides such as zineb, procymidone, carbendazim, dimethirimol, iprodione, and agricultural streptomycin in rotation for control; aphids can be controlled with yibianjing and chlorpyrifos, and mites can be controlled with propargite and fenbutatin oxide.

7. Harden strong seedlings and transplant

The seedling age in autumn seedling raising is relatively short, and hardening should be carried out promptly once true leaves grow. On sunny days, use covers for shading; in cloudy and rainy weather, the covers on the small arched shed can be lifted. Harden the seedlings gradually by following the steps of shortening the time from short to long and opening the ventilation openings from small to large, until no shading material is covered at all. Pay attention to the weather forecast at any time 1-2 days before transplanting, generally transplant in the evening of a sunny day or on a cloudy day, and make sure to transplant with pesticides, fertilizer, and soil.