On December 21, the Central Meteorological Observatory continued to issue a yellow warning for low temperatures: It is expected that from 8:00 am on December 21 to 8:00 am on December 24, the daily minimum or average temperatures in most areas of the northeastern regions of Northwest China, central and western Inner Mongolia, North China, Northeast China, the Yellow River region, and southward will be more than 5°C lower than historical averages for the same period. Among these, some areas in central Inner Mongolia, Liaoning, North China, eastern Shandong Peninsula, Huai River region, central and eastern Jiangnan, northern and western South China will be more than 7°C lower. The lowest temperature line of 0°C will be located in southern Guizhou to northern South China.

Most Tea-producing regions in our country are within the influence of this persistent cold spell. What harm can persistent low temperatures cause to tea plants? What measures should be taken to mitigate the impact of low temperatures on tea plants? Please read on…

The Impact of This Cold Spell on Tea Plants

Research suggests that when temperatures fall below 0°C, arboreal or semi-arboreal large-Leaf tea plants may suffer from frost damage, while small- and medium-leaf shrub-type tea plants typically experience frost damage at -10°C. In addition, before the low-temperature warning, there had already been significant temperature drops in various tea-producing regions, and through their own process of cold acclimatization, tea plants have enhanced their cold resistance. Therefore, it is expected that this cold spell will have little impact on most mature tea gardens, but for young tea gardens and high-altitude tea gardens, timely emergency preventive measures should be taken to minimize the harm caused by extreme low temperatures and ensure the production of Spring Tea next year.

Preventive and Rescue Measures for Frost Damage in Tea Plants

In long-term production practice, Chinese farmers have developed many effective techniques for preventing and mitigating frost damage in tea plants, achieving gratifying results. Summarized, they include the following aspects.

Physical Protective Methods

1. Using Favorable Terrain to Prevent Frost

Favorable terrain can play a role in wind protection and warmth retention: ① In southern mountainous regions and higher-latitude northern regions, sheltered sunny terrains and mountain barriers can help protect against cold and wind. ② Planting tea on slopes can help prevent frost, as slope temperatures are often 4-5°C higher than valley temperatures. ③ Surrounding tea gardens with rows of trees or protective forests can effectively shield against wind over an area 15-20 times the height of the trees. Successful examples of protective forests or row trees made of pine trees in the north, fir trees in the central region, and rubber trees in the south exist in our country.

2. Using Obstructions to Prevent Frost

Using windbreaks to prevent and reduce frost damage to tea plants has proven highly effective. According to observations, a 1.5-meter-high windbreak can have an effective windproof range of up to 7-8 meters, with a temperature increase of 0.2-5°C compared to the area before and after the windbreak. When using windbreaks to prevent frost, young tea plants should have barriers set up row by row, with the barrier height about 20 centimeters above the tea plant; for productive tea gardens, barriers should be set up around the perimeter of the garden, with a height of about 2 meters. Generally, rice straw curtains are the best choice for windbreak materials, and plastic film can also be used, achieving the purpose of “allowing light to pass in front, protecting the back, not shading the rows behind”.

3. Covering to Prevent Frost

1) Soil Burial Covering to Prevent Frost

Young tea plants can use soil burial for winter, which is simple and easy to implement with significant effects, especially ideal for 1- to 2-year-old tea plants. Soil burial should be done before the frost arrives, giving tea seedlings the opportunity to “harden off” to enhance the cold resistance of the tea plant. Both soil burial and removal should be carried out in two to three stages. If soil is buried too early in one go, the second-year tea seedlings will have weak buds and leaves. Note that during the last soil burial, 2-3 true leaves should remain above the soil, known as “exposed tops.” After the spring temperature stabilizes, soil should be removed in stages. If soil is removed too early all at once, the tea seedlings may suffer damage due to “late spring cold.”

2) Straw Covering to Prevent Frost

The use of straw covering to prevent frost is relatively common in our country's tea regions. According to observations, covering the canopy with straw can raise night-time canopy temperatures by 0.3-2°C. Additionally, straw covering reduces soil moisture evaporation and prevents frozen soil. Straw covering can be done immediately after autumn-winter Tea Garden management. Covering materials such as weeds, crop stalks, and pine branches can be placed on the ground between rows of tea plants. To prevent frost damage to tea plant leaves, straw can be laid on the canopy, generally done around the time of Light Snow (a solar term). If done too early, it affects photosynthetic accumulation in the tea plant, and if done too late, it does not achieve the purpose of frost prevention. Straw covering in tea gardens north of the Huai River should be removed in early March of the following year, and in tea gardens south of the Huai River, it can be removed earlier.

5. Smoke Fumigation to Prevent Frost

When low temperatures arrive, light smoky materials like rice straw, sawdust, rice husks, weeds, etc., in suitable corners of the tea garden according to wind direction, terrain, and area, creating a “greenhouse effect” to prevent the loss of a large amount of heat from the soil and tea plants.

Chemical Protective Methods

1. Spraying Antifreeze Agents to Prevent Frost

The chemical method of protection involves spraying certain chemical agents on tea plants before and during winter to provide insulation, reduce transpiration, promote branch and leaf maturation, and increase lignification, thereby enhancing the cold resistance of the tea plant and reducing the severity of frost damage. For mature tea plants in high-altitude regions, antifreeze agents can be sprayed on the leaves before extreme low temperatures to enhance the plant's tolerance to extremely low temperatures. Research has found that spraying calcium ions, abscisic acid, proline, betaine, γ-aminobutyric acid, and exogenous application of melatonin, brassinolide, and seaweed fermentation liquid containing brown algae oligosaccharides significantly improve the cold resistance of tea plants.

2. Spraying Bactericides or Antibacterial Liquids to Prevent Frost

Studies show that the presence of ice-nucleating bacteria on tea plant leaves is closely related to the formation of frost damage. Ice-nucleating bacteria facilitate ice formation and significantly raise the temperature at which ice hangs form, exacerbating frost damage. By spraying bactericides or antibacterial liquids, the number and activity of bacteria can be reduced and inhibited, playing a role in preventing frost damage in tea plants.

Strengthening Tea Garden Management