During the spring warming period, cold air often invades, causing a significant drop in temperature. This weather, characterized by warmth before and cold after, is known as late spring cold. Late spring cold generally refers to prolonged periods of low temperatures and overcast rainy weather after the Vernal Equinox, specifically when the temperatures in late March or early April are lower than average. Depending on the timing, it can be further divided into “Vernal Equinox Cold” and “Qingming Cold.” “Vernal Equinox Cold” occurs when the daily average temperature remains below 10°C for five days or more, with less than three hours of sunshine, from March 15 to March 27. “Qingming Cold” refers to low-temperature and rainy weather from March 28 to April 10.
The Harm of Late Spring Cold to Tea Plants:
In addition to variety, soil, fertilization, management, and processing skills, the production of high-quality tea also depends on climatic conditions. The relationship between tea production and temperature, sunlight, and rainfall is close. When the daily average temperature remains above 10°C for three consecutive days, tea buds begin to sprout and unfurl; once the temperature stabilizes above 10°C, the growth of buds and leaves accelerates, and new shoots emerge. However, during the early spring growth period of early varieties, intermittent cold air invasions occur, leading to unpredictable weather and unstable temperatures. When cold air moves southward, it often meets with warm, humid air from the south, resulting in persistent periods of low temperatures and overcast rainy weather, known as late spring cold. Generally, if the ten-day average temperature is more than 2°C lower than usual, severe late spring cold occurs. The later and stronger the cold air moves southward, the wider the area affected, and the greater the likelihood of late spring cold. Such climate conditions have a significant impact on tea production. Surveys show that when newly emerged tender buds encounter a sharp drop in temperature due to late spring cold, they can be frozen or killed, severely affecting both yield and quality.
Preventive Measures for Late Spring Cold in Tea Plants:
1. Timely Harvesting
Based on the status of sprouting buds and weather conditions, organize personnel to harvest slightly earlier before the Frost damage. Try to pick as many of the sprouted buds as possible before the impact of late spring cold, reducing losses for tea farmers.
2. Smudging to Drive Away Frost
Smudging is the most widely used and simplest method. It should be done when the temperature drops to around 2°C or 2-3 hours before a Cold wave, depending on the wind direction, terrain, and area. Light firewood in the tea field, ensuring the wood is not too dry, aiming for more smoke than flame. Smoke stacks should be evenly distributed across all directions, and smudging can increase temperatures by 0.5°C to 2°C.
3. Covering to Prevent Frost
Before the arrival of low temperatures and cold waves, cover the ground with straw, miscellaneous grass, shade nets, or mulch, or use soil. This helps retain ground heat. For example, laying straw (approximately 1500-2000 kg per mu, enough to cover the soil) on the ground under the tea plants can raise the ground temperature in covered fields by 1°C to 2°C compared to uncovered fields. This reduces soil heat radiation, retains soil moisture, and protects tea plants, enhancing their ability to resist frost.
4. Strengthening Fertilization Management
Strengthen fertilization management in tea fields by applying sufficient fermented organic manure or specialized tea plant fertilizer, which can thicken the soil layer, improve soil quality, and supplement mineral elements. Plant trees to form windbreaks on the side facing prevailing winds in tea fields or apply antifreeze agents to tea plants when they experience low-temperature frost damage, which can alleviate the effects of frost and promote the emergence of new shoots.
5. Selecting Superior Varieties
Promote the cultivation of cold-resistant tea plant varieties to effectively prevent frost damage. In areas prone to frost damage, consider introducing cold-resistant tea seedlings from nearby provinces with similar climate conditions when establishing new tea fields.
Remedial Measures After Tea Plants Suffer Frost Damage:
After frost damage, take appropriate care and rejuvenation measures based on the severity of the damage to help the tea plants recover quickly and mitigate losses:
1. Pruning
Pruning is a common post-frost damage remedial measure. Once warmer weather returns, immediately prune the damaged branches and leaves. For lightly damaged tea fields with good picking surfaces, perform light pruning to clear the canopy and promote bud sprouting. The pruning should be as light as possible to maintain the picking surface. For more severely damaged areas, deep or heavy pruning may be necessary. Prune below the point of dead branches to prevent entire branches from dying and to stimulate the emergence of dormant buds below the cut, helping the tea plants to recover vitality and resume production as soon as possible.
2. Shallow Tilling and Fertilization
Frost damage causes some trauma to tea plants, so shallow tilling and fertilization should be carried out promptly. After frost damage in the spring sprouting period, while pruning, apply water-soluble fertilizers to help restore the vitality of the tea plants and promote the sprouting of buds and growth of new shoots.
3. Cultivating the Canopy
For tea plants that have undergone light pruning after frost damage, leave one large leaf during spring tea picking; summer and Autumn Tea should be picked according to regular practices. This approach not only helps maintain a healthy canopy but also allows for the collection of high-grade teas, reducing losses caused by frost damage.