Although blueberries possess strong cold tolerance, frost damage occasionally occurs. Frost damage primarily manifests as winter dieback and flower bud damage, with dieback being the most common issue. In northern regions with high latitudes, severe winters, and prolonged periods of low temperatures, extreme cold spells frequently caused by strong cold fronts can subject blueberries to extended exposure to low temperatures. This inhibits growth and leads to frost damage, resulting in reduced yields at best and complete crop failure at worst. Flower bud damage is the next most common issue. In spring, as blueberries begin bud break and growth, their cold tolerance decreases. Temperatures around 0°C severely damage flower buds, causing tender tissues like buds to turn black or brown and die within hours after freezing and thawing cycles. During the growing season, flower buds suffer frost damage below -4°C. At flowering, temperatures as low as 3°C cause cold injury, and during fruit drop and green fruit stages, temperatures as low as 2°C can cause cold damage. Therefore, once blueberries are planted, long-term planning is essential. Effective winter protection management is critical to ensuring the plants survive the cold season. Artificial soil covering is one of the necessary techniques for successful blueberry cultivation in cold regions and a vital measure for securing productive yields.
I. Winter Protection Management
1. Timing of Soil Covering: The timing for soil covering should be determined based on local climate, soil conditions, and production scale. Closely monitor weather changes. Begin covering when average temperatures reach 5°C and soil freezes at night but thaws during the day. Soil moisture should be neither too wet nor too dry—aim for a texture where soil forms a ball when squeezed in hand but crumbles upon landing. Begin soil mounding when minimum temperatures drop to -3°C. Mounding too early risks flower bud rot due to warm, moist soil; delaying allows soil freezing, making mounding difficult and resulting in large, poorly sealed clumps that fail to provide adequate protection. Complete mounding before soil fully freezes.
2. Soil Covering Methods: Practice demonstrates that soil covering provides effective winter protection for blueberries. Insufficient coverage may cause plant freezing, reducing yield and profitability. Excessive coverage increases production costs without improving outcomes. Considering cost efficiency and mechanization, the solid soil covering method is the preferred choice. Solid soil mounding offers the safest, most reliable, and applicable protection. The mound shields plants from light, wind, retains heat, and conserves moisture. Apply a 15cm layer of soil.
3. Pre-Winter Preparation:
(1) Promote lignification: After fruit harvest, foliar spray 0.3% potassium dihydrogen phosphate every 7-10 days, applying 2-3 times to enhance tree lignification.
(2) Pre-freeze irrigation: To ensure adequate soil moisture during winter dormancy, sufficient pre-freeze irrigation is typically required. This irrigation significantly boosts blueberry cold tolerance. If rainfall is insufficient, apply this irrigation 10 days before cold protection measures.
(3) Tilling for Cold Protection: 7-10 days before cold protection, prune diseased, dead branches, and basal, tender, vigorous shoots from plants. Thoroughly till the soil in the blueberry planting furrows, leveling and finely raking it to maintain a finely crumbled texture. Prepare the soil for covering with straw mats.
4. Solid Soil Covering for Winter Protection: Procedures and Standards
Winter protection operations should be conducted during clear, sunny weather whenever possible. Methods and standards vary depending on blueberry variety and tree age.
(1) Young Trees: Lay lowbush blueberry plants flat on their southern side. Use fine soil from between rows to thoroughly cover the plant clump to a depth of 15 cm, ensuring branches remain hidden and no air gaps exist. For semi-dwarf blueberries, bend adjacent plants toward the center of the row and press them down. Use fine soil from between the rows to cover the plants completely, ensuring a thickness of 15 cm.
(2) Mature Plants: Semi-dwarf and Dwarf blueberries should be bent straight in one direction along the row. Place soil cushions at the points where branches bend to prevent breakage from excessive weight after covering. Semi-dwarf blueberry branches are particularly stiff and prone to snapping. When handling, gather the branches of the shrub, gently rock it back and forth a few times, then slowly bend it forward. Avoid excessive force to prevent breaking the branches. Increase soil mounding thickness appropriately. For blueberry fields planted in raised beds in low-lying areas, also increase mounding thickness during winter protection. Take soil from the furrows, avoiding areas too close to the roots to prevent root damage and reduced cold tolerance. The standard mounding thickness is 15 cm. Firm the soil as you mound to prevent air pockets. Ensure blueberry branches make full contact with the soil surface during mounding, eliminating any air pockets or cracks. After mounding, regularly inspect the soil cover before complete ground freezing. Pay special attention to the northwest side of the mound. Promptly replenish soil if it is blown away to prevent damage to plants from thin soil layers during severe cold. Immediately fill any gaps or cracks with soil and pack firmly.
II. Removal of Winter Protection
Once the protective soil layer has completely thawed, remove the winter protection. Start by removing the soil from the sides before removing the top layer to avoid damaging young buds. Spring frost protection should not be removed prematurely. Removing soil too early exposes roots to low temperatures and strong spring winds, preventing water and nutrient uptake. Exposed branches allow flower and leaf buds to sprout prematurely using branch nutrients. These buds, deprived of root-supplied moisture and nutrients, will gradually wither and die after swelling, and remain vulnerable to late frost damage. Removing the soil too late, however, poses risks. Rapid temperature fluctuations in spring cause the soil mound to heat up and become humid, potentially triggering premature bud break within the soil. This can lead to yellowing of tender shoots and buds. Some buds may even rot and die underground. Once exposed, the delicate stems and leaves become vulnerable to wind and sun exposure, increasing the risk of death. Due to varying climatic conditions across regions, the optimal timing for removing winter protection may differ. Timely removal of protective soil mounds promotes proper bud break and sprouting in blueberries, resulting in robust plant growth.
Post time: Aug-27-2025