Harvesting onions at peak maturity determines their final flavor, size, and potential for long-term storage. Timing the lift from the soil directly influences the protective qualities of the bulb’s outer layers. Successful cultivation relies on recognizing the plant’s biological signals that indicate its growing season is complete. Missing this narrow window can compromise the bulb, leading to premature rot or poor keeping quality.
Identifying the Visual Signals of Readiness
The most reliable indicator that an onion has finished developing its bulb is when the green foliage begins to naturally collapse. This process, known as “neck fall,” signals that the plant has ceased active growth and is redirecting energy into the subterranean bulb. Gardeners typically wait until 50 to 75 percent of the plant tops have fully flopped over before harvesting.
The collapse occurs because the neck—where the leaves meet the bulb—softens and becomes pliable. The plant stops the flow of moisture and nutrients to the leaves, causing the neck tissue to weaken and dry out. This action allows the neck to seal, creating a protective barrier for the mature bulb beneath the soil.
Along with the physical fall, the green foliage will begin to turn yellow and eventually brown, a sign of senescence. This discoloration shows that the leaves are dying back as their purpose for the season concludes. The drying and thinning of the neck tissue is a more accurate sign of internal readiness than the color change alone.
It is important to harvest soon after the tops have fallen and the neck has softened, but before the foliage is completely brown and dry. Waiting too long increases the bulb’s vulnerability to soil-borne pathogens that can enter through decaying tissue. A dry, closed neck is the plant’s natural defense mechanism, and an open neck invites spoilage.
The Physical Process of Lifting the Onions
A week to two weeks before the expected harvest date, stop watering the onion bed entirely. This preparation encourages the neck tissue to dry out quickly and helps the outer skin of the bulb firm up while still in the ground. Reducing moisture minimizes the risk of fungal diseases or molds that thrive in wet soil conditions.
When the majority of the tops have fallen, remove the bulbs with care to prevent bruising or puncturing the outer layers. Instead of pulling the tops, which can tear the neck, gently loosen the soil around the bulbs using a garden fork or small shovel. This technique reduces stress and ensures the bulb is extracted intact.
Once lifted, gently shake the bulbs to remove excess soil clinging to the roots. If the weather is dry and sunny, the onions can benefit from a short period of field curing. Laying the bulbs on the soil surface for one to two days allows the outer skins to begin setting and the necks to continue drying.
The bulbs must be protected from direct sunlight during this initial drying phase, which can cause sunscald. If a covered porch or shed is unavailable, the foliage of the harvested onions can be draped over the bulbs for shade. If rain or high humidity is expected, move the onions immediately to a protected, well-ventilated area to prevent re-moisturization.
Curing and Preparing Onions for Long-Term Storage
Curing is a post-harvest step that prepares the bulbs for extended storage by hardening the outer skin and sealing the neck. The proper curing environment requires a warm, dry location with excellent air circulation, ideally between 75 and 80 degrees Fahrenheit. This process is accelerated dehydration that prevents internal moisture from causing rot.
The onions should be spread out in a single layer on a wire rack or hung in mesh bags to ensure maximum airflow. This setup prevents moisture accumulation, which is the primary cause of premature decay. The curing period typically lasts between two and four weeks, depending on the ambient temperature and humidity levels.
A fully cured onion will have a dry, papery outer skin that rustles when touched and a neck that is withered and dry. This tightly sealed neck confirms that moisture transfer has ceased and the bulb is fully dormant. Any onions that remain soft at the neck or show signs of bruising should be set aside for immediate use, as they will not store well.
Once curing is complete, preparation for storage involves trimming both the roots and the dried tops. The roots should be clipped close to the basal plate of the bulb, and the dried foliage should be cut down to a one to two-inch stub. The prepared onions can then be moved to a final storage location that is cool, dark, and dry, ideally between 35 and 40 degrees Fahrenheit.