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Overwintering lettuce is easy to crack and prevent water and water
When harvesting wintering lettuce, it's common to notice cracks in the stem, which can significantly reduce its market value. Severe damage often leads to soft rot and sclerotinia, causing the affected areas to turn dark brown. This issue is particularly problematic during the stalk hypertrophy phase, when the plant requires adequate nitrogen and water to promote rapid growth of the tender stem. However, in the late stage of this period—especially close to harvest—overwatering or heavy rain can cause the base of the stem to split vertically.
This cracking is mainly due to environmental or management factors. As the harvest date approaches, the outer layer of the tender stem becomes hardened. If there is excessive rainfall or irrigation at this time, the internal part of the stem grows quickly, creating swelling pressure. Meanwhile, the hardened skin exerts inward wall pressure. Since the swelling pressure exceeds the wall pressure, the stem splits along its length. In high humidity conditions, this creates an ideal environment for pathogenic bacteria to thrive, increasing the risk of disease. This phenomenon is more common in spring lettuce cultivation, where heavy rains are frequent. In autumn, if early growth is poor, sudden rain or excessive watering later on can also lead to stem cracking.
Once the stems have cracked, it’s difficult to reverse the damage, so prevention is key. During the early rejuvenation stage of wintering lettuce, it's important to carefully manage fertilization and irrigation to encourage leaf expansion and nutrient accumulation for stem growth. Once the plant enters the "lotus sitting" phase, the number of leaves increases significantly. When the heart leaf and lotus leaf become flat, the stem begins to grow rapidly. At this point, frequent fertilization is necessary, with a focus on nitrogen and potassium. Apply 15 kg of urea or ammonium sulfate per acre, along with 20 kg of potassium sulfate. If available, apply 1-2 times of large manure water, each time around 1000-1500 kg. However, avoid over-fertilizing and do not apply too late, as this can harm the plant.
Water management is equally critical during this period. The soil should not be allowed to dry out, but overwatering must also be avoided. Excessive moisture can cause the stem to swell too quickly, leading to cracking. Watering should be done in small, even amounts to prevent stress on the plant. In the final weeks before harvest, it's best to limit watering and ensure proper drainage to avoid unnecessary moisture buildup. Timely harvesting after rain is also essential to minimize the risk of stem cracking.