Spinach is a cold-tolerant leafy vegetable that thrives in specific temperature and light conditions. Mature spinach plants can survive winter in regions where the minimum temperature drops to around -10°C, making it suitable for open-field cultivation in areas like North China, Northeast China, and Northwest China. In colder regions where temperatures fall below -10°C, using wind barriers or non-woven covers can help protect the plants. Some cold-resistant varieties can even withstand short periods of extreme cold, such as -30°C, with only the outer leaves freezing. However, young seedlings with just 1–2 true leaves are more vulnerable and have weaker cold resistance.
For optimal germination, spinach seeds require a minimum temperature of 4°C, with the best results occurring between 15–20°C. Germination usually takes about 4 days under ideal conditions, with a high germination rate of over 90%. If temperatures rise above 35°C, the germination rate drops significantly, often below 20%. Therefore, during hot seasons, it's essential to pre-soak and germinate seeds in cooler environments to ensure better success.
Spinach is a long-day plant, meaning it responds strongly to extended daylight hours. In places like Shaanxi’s Guanzhong region, spinach sown in June or July begins flower bud differentiation within 17–19 days, under conditions of 14–15 hours of daily sunlight and average temperatures of 24.6–24.9°C. This shows that long days are crucial for flower development, even without low temperatures. However, when daylight is reduced to less than 12 hours, applying a low-temperature treatment (around 2°C) can speed up flower bud formation. This knowledge is important for managing spinach growth in autumn, especially when aiming to delay flowering for better harvest quality.
Once flower buds form, the development of reproductive structures accelerates with increasing temperature and longer daylight. To maximize yield and quality, the ideal sowing time should allow the initial growth phase (leaf development) to occur in temperatures between 20–25°C. After flower bud differentiation, lower temperatures and shorter days help extend the vegetative growth period, leading to larger, more robust plants.
Water spinach, another variety, has high water content (about 92%) and requires consistent moisture. It performs best in environments with 80–90% humidity and soil moisture levels of 18–20%. Dry conditions slow down leaf growth, increase fiber content, and reduce quality. During hot weather, water stress can cause premature flowering and an imbalance in male-to-female plant ratios, which negatively affects harvest.
Soil pH is also important for spinach. Slightly acidic to neutral soils (pH 6.0–7.0) are ideal. In overly acidic soils, plants grow slowly, and leaves may yellow and become tough. Adding lime or wood ash can help adjust the pH. Nutrient management is critical: nitrogen, phosphorus, and potassium are all necessary. Excessive focus on nitrogen can lead to poor overall plant development, as shown in experiments where spinach without phosphorus and potassium had significantly lower yields. Boron deficiency can cause curled, yellowed leaves, so applying borax at 0.5–0.75 kg per acre or foliar spraying helps prevent this.
Spinach grows well in various soil types, including sandy loam, loam, and clay loam. For early spring markets, sandy loam is preferred because it warms up quickly, allowing for faster regrowth after winter. For higher yields, richer soils like loam or clay loam are better suited. Overall, understanding the interplay of temperature, light, water, and soil conditions is key to successful spinach cultivation.
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