Greenhouse Design and Seedling Cultivation Techniques
Our region lies between 42°09′ and 42°14′ north latitude, classified as a supplemental heating zone. It is well-suited for long-slope solar greenhouses, which maximize solar gain during the winter months.
1. Structural Design
- **Angle**: The front roof angle should match the angle of direct sunlight on the winter solstice, typically around 90 degrees minus that value. The back roof's elevation angle should be greater than the local latitude to optimize heat retention. The azimuth should be adjusted based on morning fog, with a preference for 5–10 degrees westward to capture more sunlight.
- **Height**: The height from the ground to the highest point of the roof should not be less than 3.2 meters. A lower back wall, ideally around 2.7 meters, helps improve insulation.
- **Span**: The distance from the inner side of the back wall to the front roof should be between 6.8 and 7.2 meters. Spans over 8 to 10 meters may reduce insulation efficiency.
- **Length**: The east-west length of the greenhouse should not exceed 100 meters to ensure even temperature distribution.
- **Thickness**: The back wall should be at least as thick as the local permafrost layer. The back slope should be 45–60 cm thick, and the straw curtain should be over 6 cm thick.
- **Ratios**: The front-to-back slope ratio should be approximately 4.5:1. The high-to-high ratio is usually 1:2.1 to 2.4. The insulation ratio (floor area to front room area) should be close to 1 for optimal performance. The shade ratio is calculated by doubling the height of the greenhouse to determine the spacing between structures, including the straw curtain thickness.
2. Construction Principles
Choose a site that is sheltered from the wind, receives ample sunlight, has low groundwater levels, and is away from chemical plants. Greenhouses should generally face south, with a slight westward tilt of about 10 degrees. They should be extended towards the back slope for better thermal stability. After construction, cold-proof ditches should be dug, and temporary flue gas systems should be installed to prevent damage from severe weather. For temporary wind protection, crosswise wind riveting is recommended.
Seedling Raising Techniques
Previously, we used nutrient soil for seedlings, but this often led to poor permeability and compaction, which hindered root development and reduced seedling quality. In 2006, we introduced a combination of nutrient matrix and vermiculite, which significantly improved results. Pepper and tomato seedlings successfully transplanted into the field with survival rates exceeding 95%.
1. Preparation of the Nursery Area
If using a greenhouse for seedling cultivation, it’s best to preheat the space. Our team usually prepares the nursery in mid-February.
2. Site Preparation
Before placing the seedling trays, level the ground to make efficient use of space and facilitate operations. Construct small baskets every 2.64 meters, 20 cm high and wide.
3. Installing the Trays
Mix the nutrient substrate with vermiculite in a 2:1 ratio. Water the mixture appropriately before placing it into the trays. New trays can be used directly, while old ones should be disinfected using trisodium phosphate. Ensure the substrate has 70% moisture. Once the tray is filled, level it with a flat board, place 10 trays, press them evenly, and then sow the seeds at a depth of 1–1.5 cm.
4. Sowing
Before sowing, disinfect the seeds using chemicals such as quintozene, chlorothalonil, or Fushizhuang. Spray the seeds thoroughly. Check the moisture the next day—darkened substrate indicates sufficient moisture. If it's too dry, water it. Cover the tray with a film and maintain a temperature of 28–32°C. Once over 70% of the seeds show white tips, remove the film. Ensure all seedlings emerge within 8 days; otherwise, their quality may be compromised. If seedlings are still under the soil, spray gently without spilling. Keep the cover on at night to maintain stable temperatures.
5. Post-Emergence Care
After emergence, lower nighttime temperatures to 7–12°C to prevent leggy growth. Daytime temperatures should not exceed 25°C, and nighttime temperatures should remain above 7°C. At midnight, gradually lower the temperature. During the day, open a small vent to regulate temperature. Use a thermometer placed in the tray to monitor the substrate temperature. When it reaches 5°C, root growth stops, leading to yellowing. Avoid overwatering; instead, manage humidity through temperature control. If the substrate becomes too dry, roots may die. If this occurs, secondary roots may develop at the base if water is replenished promptly. Do not fill the tray with water more than 1 cm below the surface. Water thoroughly in the morning if needed.
Light plays a key role in preventing legginess. Move the seedlings 2–3 times during the growing period. During high temperatures, provide partial shade, and during cooler periods, increase light and ventilation. Maintain a temperature of around 22°C in the nursery. Transplant seedlings 7–10 days before planting. Gradually acclimate the seedlings by opening the spacing between the trays to allow the roots to harden.
When the seedlings have 2–3 true leaves, apply a solution of 0.3% urea and 0.15% potassium dihydrogen phosphate. Alternate watering and fertilizing, and transplant when the seedlings reach 40 days of age, with 4 leaves and one heart.
6. Pest Control
Regularly spray for pests and diseases. Use products like Po Like or Triplicate Dry Net alternately, applying them every 7 days.
7. Strong Seedling Standards
Healthy seedlings should have white roots, be 8–12 cm tall, have 4–4.5 leaves, and a stem thickness of 0.5 cm. The base of the stem should be lignified, and the leaves should be dark green.
8. Precautions
- Use reservoir water for irrigation.
- Cover the bottom of the seedling trays with plastic film.
- Install windbreaks before the season begins to protect the seedlings from direct wind.
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