As one of the most promising sectors in agricultural development, the advancement of plastic greenhouses has significantly improved the working conditions for vegetable farmers and boosted the local vegetable supply. This innovation has led to a substantial increase in the income of growers, with an average yield per mu reaching over 20,000 yuan, which is only a few thousand yuan less than the maximum potential. In this article, we focus on Cucumber cultivation, along with Tomato planting management within plastic greenhouses, aiming to provide practical guidance for farmers.
First, greenhouse temperature management plays a crucial role. Based on local weather conditions, the plastic film is usually installed around mid-September and removed by mid-October. The key principle is to maintain the minimum temperature, limit the maximum temperature, and extend the optimal temperature range. Cucumbers stop root growth below 12°C and are at risk of frost damage when temperatures drop below 5°C. Thus, the minimum temperature should always be kept above 10°C.
The ideal temperature for cucumbers is between 25–28°C, with a maximum of 35°C. It's important to maintain the optimal temperature for 6–8 hours daily. When the temperature drops to 20°C, windows should be closed promptly, especially during bad weather. At 15°C, straw curtains should be put up. During cold spells, they can be covered at 17–18°C, raising the temperature by 2–3°C. Throughout the day, the temperature should stay between 22–25°C, while at night it should remain between 16–20°C, and around 10–16°C in the middle of the night. In severe weather, morning temperatures may drop to 8°C or even 5°C, but as long as it doesn't go below 5°C, the plants won’t be harmed. If it does, chilling damage can occur. Therefore, enhancing insulation is essential—greenhouses must be built according to design standards, leaks should be fixed promptly, and additional cold skirts should be added before winter to ensure proper warming during extreme weather.
Winter ground temperatures are a major constraint for cucumber production. To address this, efforts should be made to raise the soil temperature. Studies show that increasing the ground temperature by 1°C is equivalent to raising the air temperature by 2–3°C. Therefore, digging cold-proof trenches in front of the greenhouse, covering the film, and reducing water flow during winter are all effective measures. Water used for irrigation should also be preheated to prevent excessive temperature drops.
For tomatoes, the maximum temperature should not exceed 30°C, with an optimal range of 20–25°C and a minimum of 6–10°C. Eggplants require a maximum of 35°C, an optimal range of 25–30°C, and a minimum of 10°C.
Second, lighting management is critical. Extending daylight hours and improving light intensity can greatly enhance productivity. As soon as sunlight appears in the morning, the cover should be lifted. High-quality polyvinylidene chloride films with good light transmission and insulation properties are recommended. Dust on the film should be cleaned regularly to maximize light penetration. Both direct and scattered light should be utilized, and reflective screens or mulch films can be used to improve lighting efficiency.
Third, fertilization is essential. A solid base fertilizer application is the foundation, and careful top-dressing is crucial. For solar greenhouses, where vegetables grow for a long time, it’s important to apply sufficient base fertilizer—typically 5,000 kg of organic manure, 200 kg of cake fertilizer, and 75 kg of compound fertilizer per mu. These should be applied in two-thirds initially and the rest in one-third increments. Organic fertilizers not only nourish the plants but also release carbon dioxide through microbial decomposition, boosting greenhouse CO₂ levels and enhancing yields. During the pre-harvest period, three top dressings are typically done. However, cucumbers are sensitive to excess nutrients, so top dressing should be done in small amounts. During normal growing seasons, watering and fertilizing should be spaced out, with no more than 15 kg of urea per acre each time. In winter, due to limited irrigation, fertilization should be adjusted based on plant health. Foliar sprays can also help boost production.
Fourth, water management is vital. Planting water should be given sparingly, and excessive watering should be avoided. After planting, watering is generally not needed unless there's a drought. Early watering can lead to excessive vine growth, affecting fruit setting and causing issues like "pharmaceutics." Watering should begin only when the fruits reach 15–16 cm in length and turn dark green. During the growing season, watering should be even, allowing the soil to dry slightly between sessions to promote good ventilation. A simple indicator is the dryness of the surface. Watering should be done every 15 days in winter, preferably on sunny days at noon, using drip irrigation if possible. After April, watering frequency increases to every 7 days. The rule is to water before harvesting, not after.
Fifth, managing humidity and gas composition inside the greenhouse is equally important. Due to the moisture-retaining properties of the film, indoor humidity often remains high, especially in winter, creating favorable conditions for diseases. Ventilation is necessary to reduce humidity, even during cold periods, to avoid freezing the plants. In spring and autumn, dehumidification should be prioritized, keeping humidity below 85%. Ventilation also helps regulate COâ‚‚ levels, which are often low in enclosed spaces. Maintaining a COâ‚‚ concentration of 0.03% is essential. Carbon dioxide gas fertilizers can be applied, starting half an hour after opening the curtains and ending half an hour before ventilation, with a maximum concentration of 0.15%. Ammonia and other harmful gases should also be vented after fertilization.
Sixth, plant adjustment is essential for maximizing yield. Early vines should be trained in an S-shape to encourage curvature and better sunlight exposure. When the northern end reaches 1.7 meters, the southern end should spread toward the roof, forming a north-high, south-low gradient. Diseased or old leaves should be removed promptly, but the lower part should retain 5–7 leaves to ensure each plant has 20–30 leaves. Small lateral branches and male flowers should be pruned early, and tendrils should be removed to reduce nutrient consumption. Pest control should also be maintained throughout the process.
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