Greenhouse Structure and Seedling Cultivation Techniques
Our district is located between 42°09′ and 42°14′ north latitude. It falls within a supplemental heating zone, making it ideal for long-slope solar greenhouses that maximize solar gain during the winter months.
1. Structural Design
The angle of the front roof should be equal to 90 degrees minus the angle of direct sunlight on the winter solstice. The back roof should be inclined at an angle greater than the local geographic latitude. The azimuth angle should be adjusted based on morning fog conditions, with optimal sunshine exposure ranging from 5 to 10 degrees westward.
The height from the ground to the highest point of the roof should not be less than 3.2 meters. A lower back wall is preferable, typically around 2.7 meters. The span, measured from the inner side of the back wall to the front roof, should be between 6.8 and 7.2 meters. If the span exceeds 8 to 10 meters, insulation performance may decrease.
The length between the east and west gables should not exceed 100 meters. The back wall thickness should match the local permafrost layer, while the back slope should be between 45 and 60 cm thick. The straw curtain should be more than 6 cm thick.
The front-to-back slope ratio is typically 4.5:1, and the high-to-high ratio ranges from 1:2.1 to 1:2.4. An ideal insulation ratio is when the floor area is nearly equal to the front room area. The shade ratio is calculated as twice the height of the highest point, which determines the spacing between greenhouses, including the thickness of the straw curtain.
2. Construction Principles
Choose a site that is leeward, sunny, has low groundwater levels, and is away from chemical plants. Greenhouses should face south with a slight western orientation (about 10 degrees). They should be extended toward the back slope. After construction, cold-proof ditches should be dug. Temporary flue gas channels are necessary to prevent damage from severe weather. For temporary wind protection, crosswise fastening is recommended.
Seedling Raising Techniques
Previously, we used nutritious soil for seedlings, but this method had issues with poor permeability and compaction, which hindered root development and affected seedling quality. In 2006, we introduced a combination of nutrient matrix and vermiculite, which significantly improved results. Pepper and tomato seedlings successfully transitioned to the field with a survival rate above 95%.
1. Nursery Shed Preparation
If using a cold house for seedlings, the shed should be heated in advance. Our team usually starts preparing in mid-February.
2. Ground Preparation
Before placing the seedling trays, level the ground to optimize space and ease of operation. Construct small baskets every 2.64 meters, 20 cm high and 20 cm wide.
3. Installing Seedling Trays
The nutrient substrate to vermiculite ratio is generally 2:1. Mix the water properly, and new trays can be installed directly. Old trays should be disinfected by soaking them in a trisodium phosphate solution. The substrate should have 70% moisture. Once the tray is leveled, use a flat board to press down 10 trays, each 1 inch deep, ensuring even pressure. Then, sow seeds at a depth of 1 to 1.5 cm.
4. Sowing
Before sowing, treat seeds with chemicals like quintozene, chlorothalonil, or Fushizhuang. Spray evenly and thoroughly. Check moisture the next day—deeply soaked substrates indicate sufficient moisture, while shallow ones need more. Cover the trays with plastic film. Maintain pre-emergence temperatures between 28–32°C. Once over 70% of seeds show white tips, remove the film. Ensure all seedlings emerge within 8 days; otherwise, they may not meet standard requirements. If the seedlings are exposed during emergence, spray carefully without overwatering. Keep the cover on at night to maintain stable temperatures.
5. Post-Emergence Management
After seedlings emerge, lower nighttime temperatures to 7–12°C to prevent leggy growth. Daytime temperatures should not exceed 25°C, and nighttime minimums should stay above 7°C. At midnight, gradually reduce temperatures. During the day, open small vents to regulate temperature. Insert a thermometer into the plug tray. When the substrate reaches 5°C, root growth stops, leading to yellowing. Avoid overwatering in the plug trays; adjust humidity through temperature control. If humidity is too low, roots may dry out, affecting growth. If this occurs, secondary roots may appear after timely watering. Water only when necessary, and always in the morning.
Light helps prevent legginess. Move seedlings 2–3 times during the nursery phase. During high temperatures, provide some shade, while during cooler periods, ensure strong light and proper ventilation. Maintain a shed temperature around 22°C. 7–10 days before planting, begin acclimating the seedlings. Gradually release air and increase spacing between trays to encourage root aging and growth.
When seedlings have 2–3 true leaves, apply a solution of 0.3% urea and 0.15% potassium dihydrogen phosphate. Water one day and fertilize the next. Aim for a 40-day-old seedling with 4 leaves and one heart before transplanting.
6. Pest Control
Regularly spray for pests and diseases. Use products like Po Like or Triplicate Dry Net alternately, once every 7 days.
7. Strong Seedling Standards
Healthy seedlings have white roots, are 8–12 cm tall, have 4–4.5 leaves, and a 0.5 cm thick stem. The base should be lignified, and the leaves should be dark green.
8. Precautions
Use reservoir water whenever possible. Cover the bottom of the seedling trays with plastic film. Install wind barriers to protect the seedlings from direct wind. Set up windproof film before the season begins.
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