Curing onions is a straightforward post-harvest process necessary to prepare the bulbs for extended storage. This involves carefully drying the outer layers and the neck of the onion, creating a tough, papery barrier. The purpose of curing is to seal the bulb, preventing the entry of moisture and pathogens that cause rot and decay. This preservation step induces dormancy, ensuring the onions maintain quality and firmness for many months after harvest.
Harvesting and Pre-Curing Preparation
The moment to harvest onions for long-term storage is indicated by the plant’s natural decline, specifically when the tops begin to turn yellow or brown and fall over. This collapse of the neck signals that the plant has ceased putting energy into leaf growth and the bulb has reached its maximum size. Wait until about half of the foliage has naturally fallen over before beginning the harvest.
Once the tops have flopped, carefully loosen the soil around the bulbs and lift them gently, taking care not to bruise the outer layers. Immediately brush off any large clumps of soil clinging to the bulbs, but resist washing them, as added moisture encourages spoilage. Leave the neck and stem intact, as this foliage will be used in the hanging process and will continue to draw moisture out of the bulb during the initial drying phase.
Executing the Hanging Cure
The success of the curing process requires a warm, dry, and highly ventilated environment. Ideal conditions are a temperature range between 75 and 90°F with low humidity, protected from direct sunlight and rain. Hanging the onions maximizes air circulation, which is a primary defense against mold and fungal growth.
For soft-neck varieties, which have pliable stems, the traditional method is to braid the dry foliage together into long strings, allowing the bulbs to hang freely. Hard-neck onions or those with stems too dry to braid can be tied in small bundles of three to five, using twine wrapped around the stems just above the bulbs. Alternatively, place them in open-weave mesh bags to ensure constant airflow.
Air movement is particularly important to speed up the drying of the neck, which is the last part of the onion to fully cure and the most common entry point for storage diseases. If natural airflow is insufficient due to high humidity, setting up an oscillating fan can accelerate the process. The hanging method allows for easy inspection, ensuring that damaged or diseased bulbs can be quickly removed before they contaminate the rest of the harvest.
Assessing Completion and Long-Term Storage
Curing is complete when the bulb is sealed and dry, typically taking between two to four weeks depending on the climate and humidity. A fully cured onion will have an outer skin that is thin, papery, and brittle, often making a rustling sound when handled. The neck connecting the bulb to the foliage must be completely dry, tight, and constricted, feeling firm and not slippery when pinched.
After verifying the bulbs are fully cured, prepare them for long-term storage by trimming the foliage and roots. If the onions were braided, the braid is left intact. If they were bundled, the stems should be trimmed down to about one or two inches above the bulb. All roots should be clipped close to the base, and any loose outer skin can be gently brushed away.
To maximize storage life, which can extend up to nine months for pungent varieties, the cured onions must be moved to a final storage location. This space needs to be cool, dry, and dark, with an ideal temperature range between 32 and 40°F. Continued ventilation is necessary to prevent condensation, so the bulbs should be stored in breathable containers like mesh bags or hanging braids, kept away from moisture.