Red Fuji apples often face challenges in the middle and southern plains of Hebei, where they tend to have low sugar levels and poor color development. However, with proper cultivation techniques, it is possible to significantly improve both the sweetness and appearance of the fruit. Based on our experience, here are the key practices that have proven effective:
First, ensure adequate sunlight. The sugar content of Red Fuji apples is closely linked to the light intensity within the tree canopy. Proper pruning is essential to maintain good light penetration. After winter pruning, the number of branches per acre should be kept between 70,000 and 80,000, while during the growing season, it should be maintained at around 100,000 to 120,000, ensuring a canopy transmittance of approximately 25%.
Second, implement rational fertilization. In early autumn, apply organic fertilizer such as well-fermented manure or cake fertilizer. For every kilogram of fruit produced, apply about 1.5 kg of organic matter, and consider intercropping green manure crops like white clover or alfalfa to enhance soil fertility. It’s important to limit nitrogen use and increase phosphorus and potassium, especially in the later growth stages. This can boost the coloring index by 24.4% and sugar content by 2.4%. Foliar sprays, such as potassium fulvic acid diluted 400 times, applied 3–4 times during the growing season, can also enhance fruit quality. Spraying amino acid-based solutions before coloring can advance the ripening process by 12–17 days, improving color by 24.2% and increasing sugar content by 0.9% to 1.6%. Additionally, boron application during flowering can further support fruit quality.
Third, use wall bees for pollination. Wall bees are highly efficient, and when paired with properly configured pollination trees, they help produce sweeter, better-colored, and more uniformly shaped fruits.
Fourth, manage drainage carefully. Excessive rainfall during the late growth stage negatively affects both sugar accumulation and color development. Avoid flood irrigation unless there's a severe drought. When rain is heavy, make sure to drain water from the tree bases promptly.
Fifth, choose the right rootstock. Different rootstocks significantly impact fruit coloration. For example, when grafted onto Guoguang or Marshal rootstocks, the coloring index reaches 71.1% to 76.8%, while M26 dwarfing rootstocks also show excellent results.
Sixth, use fruit bags. Double-layered paper bags are recommended, and they should be applied within 35 days after flowering. Remove the outer bag one week later and the inner bag 20–30 days before harvest. Always pick the fruit on sunny, windless days between 9:00 am and 5:00 pm.
Seventh, lay reflective mulch under the tree. After removing the bags in late September, placing reflective film helps enhance coloration on all sides of the fruit.
Eighth, remove leaves and turn the fruit. Once the sunny side starts to color, gently remove shading leaves, starting from those near the fruit. After 10–12 days, rotate the fruit so the shaded side faces the sun, securing it with a small piece of transparent tape. This should be done between noon and 4:00 pm to avoid damage.
Ninth, spray regularly. Water spraying, especially in the evening, helps clean leaves, improve photosynthesis, reduce tree temperature, and enhance the day-night temperature difference, which boosts sugar accumulation and color development. Start this practice in September, using a clean sprayer to mist the leaves after 5:00 pm.
Tenth, harvest at the right time. Harvest in batches 20–30 days after bag removal, ideally in early November in the central and southern regions of Hebei for optimal quality.
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