Calcium, boron and zinc: preventing young-fruit drop and cracking in fruit trees
Most young-fruit drop and cracking is caused by calcium, boron and zinc shortage, not pests. The role of each nutrient, deficiency signs and a suggested schedule.
Young-fruit drop and fruit cracking cause the biggest losses in durian, citrus, mango and longan. In most cases the culprit is not pests or disease but a shortage of three key secondary and micronutrients: calcium (Ca), boron (B) and zinc (Zn).
Calcium: the cell’s framework
Calcium builds cell walls and the “cement” between cells. Deficient fruit has thin, brittle skin that splits when fruit swells after rain, and weak stalks that drop. Calcium moves poorly inside the plant, so it must be applied early and repeatedly, ideally in a leaf-absorbable form.
Boron: the key to pollination and fruit set
Boron drives pollen germination, pollen-tube growth and sugar transport into fruit. Without it, trees flower heavily but set little, shed young fruit and produce misshapen or corky fruit. Only small doses are needed, but timing matters: before flowering and right after fruit set.
Zinc: the regulator of shoots and leaves
Zinc is needed to synthesise auxin, the hormone that controls shoot growth and fruit development. Deficiency shows as small, clustered leaves, short shoots and small fruit; zinc also improves tolerance to weather swings.
Suggested schedule for fruit trees
- 10–15 days before flowering: spray Ca-B-Zn for healthy flowers and better set.
- 7–10 days after fruit set: repeat to limit physiological drop.
- Rapid fruit growth: 2–3 sprays 10–15 days apart, calcium-led, to prevent cracking.
- Soil: correct pH and add calcium on acid soils with ultra-fine calcium carbonate.
Why choose organic chelates
Calcium, boron and zinc chelated with amino acids and fulvic acid are absorbed faster, precipitate less in tank mixes and do not scorch leaves like inorganic salts. In the EUCHEM range, Calcium Boron Zinc is for foliar use, Sam Canxibo for soil correction and Magzin for magnesium-zinc on leaves.
Precautions
- Never mix calcium products with phosphate, sulfate or copper-based products.
- Excess boron is toxic – follow label rates.
- Wet young fruit and leaves evenly, early morning or late afternoon.
Call 0967 383 499 for a detailed spray schedule by crop and stage.
