When to harvest onions: look at the plant, not the bulb
The onion is a biennial plant grown as an annual crop. It is sown between autumn and spring and harvested in summer, generally from June to August.
The right time to harvest is determined by observing the stem, which turns yellow and begins to bend towards the ground.
Early varieties can be harvested once the bulbs have reached an acceptable diameter and the outer skins have dried sufficiently.
Two harvesting methods: traditional and direct harvesting
Traditional harvesting
The bulbs are mechanically lifted, arranged in windrows and left to cure in the field.
Curing takes place in the sun for a period that varies according to weather conditions and the variety.
Direct harvesting
In a single operation, the machine cuts the leaves 3–10 cm above the bulb, lifts the onions and transfers them into pallet boxes or trailers for immediate transport to the storage facility.
This method reduces handling time, increases storage capacity and improves air circulation inside the containers.
Onion storage: temperature, humidity and ventilation
Once curing is complete, onions can be stored either at ambient temperature or in a cold-storage facility.
The most suitable option depends on the required storage period, the variety and the intended market.
In both cases, the three key parameters are:
– temperature;
– relative humidity;
– ventilation
Managing these factors together is the key to extending shelf life.
The temperature should be kept either above 25°C or close to 0°C. Intermediate temperatures encourage sprouting, fungal growth and shrivelling.
Storage at ambient temperature
Ambient storage preferably requires facilities equipped with forced ventilation systems, allowing temperature and relative humidity to be regulated.
White onion varieties must be stored in dark conditions to prevent greening.
Technical parameters for indoor curing
Airflow
300 m³/t/h
Air temperature
25-35°C
Relative humidity
Below 75%
Post-harvest chemical treatments
Not authorised
Cold storage
Cold storage helps preserve onion quality over an extended period.
Once thoroughly cured, the bulbs can be stored in pallet boxes or in bulk piles.
Bulk storage makes it possible to use the same facility for the final curing stage and provides more uniform ventilation.
This method allows onions to be stored for up to 4–8 months.
Technical parameters for cold storage
temperature
0°C
Relative humidity
70-75%
Maximum storage period
4–8 months, depending on the cultivar
Maximum bulk-pile height
3 metres
Taking onions out of cold storage: key precautions
At the end of the storage period, the temperature must be raised gradually to prevent moisture from condensing on the bulbs.
Condensation creates favourable conditions for pathogen development and root growth.
A gradual return to ambient temperature helps protect product quality until the onions are marketed.
Transport: the final link in the quality chain
Transport vehicles must be well ventilated to prevent moisture condensation. The onions must also be stacked in a way that ensures proper air circulation and load stability.
For long-distance journeys, mixed loads should be avoided. Volatile compounds released by onion bulbs may transfer unusual odours to other products transported in the same vehicle.
During winter, protection against temperatures below the freezing point of onions, approximately −1°C, may be necessary on certain routes.
The importance of logistics
Efficient logistics management is essential for preserving the quality of the harvested crop.
APOD members can rely on a dedicated service covering product collection, storage, sorting and transport through to final delivery, ensuring traceability, punctuality and the highest level of care at every handling stage.
Pre-processing and grading: adding value before sale
Before sale, the cured product should undergo careful pre-processing.
Sorting the bulbs into groups according to size makes it easier to organise both storage and marketing.
This allows each batch to be removed from cold storage at the most suitable time, taking into account its specific characteristics and expected market prices.
Want to improve onion growing and post-harvest management?
APOD supports its members throughout every stage of the supply chain, from technical advice in the field and post-harvest quality management to logistics.
Frequently Asked Questions About Onions
When are onions harvested?
Early varieties may be harvested once the bulbs have reached a suitable diameter and the outer skins are well developed.
How are onions cured after harvesting?
What is the ideal temperature for storing onions?
Intermediate temperatures encourage sprouting, fungal disease development and quality loss.
How long can onions be stored?
How can onions be prevented from sprouting during storage?
A gradual return to ambient temperature after cold storage also helps preserve bulb quality.
