Role of Calcium in Onion Production

Calcium is a key component of cells maintaining the structure of cell walls and stabilizing cell membranes. It also has a direct influence on the salt balance within plant cells and activates potassium to regulate the opening and closing of stomata to allow water movement from the plant. Calcium enhances pollen germination; regulates some enzyme systems; and influences the growth and health of cells and conductive tissues.

Calcium effect at growth stages

Stage Calcium effect
Vegetative Growth Maintain vigorous, healthy leaf growth and to build plant supplies prior to bulbing
Bulb Formation Ensure good supply to the bulb to maximize eventual storage quality
Bulb Fill Maintain good bulb firmness and quality with reduced storage problems
See more on Onion Growth Stages.

General guidelines for Calcium application

Calcium is probably the third most important nutrient needed by onions and has a key role to play in maintaining crop quality. Calcium nitrate is particularly useful applied early to improve establishment, ensuring crops are quick to reach a desired height before transplanting. Although relatively low, levels of calcium in the bulbs are critical for storage and quality, improving the strenght of the cells.

Calcium deficiencies in onion

Leaf tips – or short lengths of the leaf - die back, without any previous yellowing of the leaf, causing the top of the leaf to fall over and die. Onion bulbs are of low density and reduced quality, and have softer skins.