The timing of onion harvest is paramount for anyone aiming to preserve their crop for long-term use. Harvesting at the wrong time, whether too early or too late, compromises the bulb’s ability to store well. The onion bulb is a storage organ, and proper maturity signals that the maximum amount of energy has been successfully transferred from the foliage to the bulb. For the home gardener, correctly interpreting these signals is the difference between an onion that lasts for months and one that rots within weeks.
Visual Indicators of Readiness
The most reliable sign that an onion is ready for harvest is the natural collapse of the plant’s green top. This occurs because the “neck,” where the leaves meet the bulb, softens and breaks down, preventing further nutrient transfer. This process, known as senescence, should occur naturally, signaling the completion of the growing cycle.
The onion is ready to be lifted when 50% to 80% of the green tops have turned yellow and fallen over. Waiting for this percentage ensures the bulb has developed a sufficient protective outer skin, which is important for curing and storage. Another physical cue is the softening of the neck itself; if you gently squeeze the neck area and it feels limp rather than firm, the energy transfer is complete. Depending on the variety, this maturation typically occurs 90 to 120 days after planting.
Once these visual cues appear, prepare the soil and the bulbs for removal. The final two weeks before harvest are focused on drying out the bulbs while they are still in the ground. Gardeners should completely stop watering the onion patch one to two weeks before the planned harvest date. This cessation of moisture helps the outer layers of the bulb begin to dry and cure, hardening the skin and promoting better storage life.
Executing the Harvest
When the tops have sufficiently flopped and the weather is dry, the physical removal of the bulbs can begin. Gently lift the onions rather than pulling them by the tops, as this rough action can bruise the bulb or cause the neck to tear, creating entry points for pathogens. A garden fork inserted a safe distance away is the best tool to carefully loosen the soil before the onion is gently pulled out.
Careful handling is important because any damage to the bulb can lead to premature rot during storage. The entire plant, including the roots and the dried foliage, should remain intact after removal. The tops act as a handle and the neck remains a temporary seal, both needed for the next step of preservation. After lifting, gently brush away the largest clumps of soil without washing the bulbs, which would reintroduce unwanted moisture.
The Critical Curing Process
Curing is a drying period immediately following harvest that is necessary to maximize the onion’s storage potential. This process seals the outer skin and dries the neck tissue, creating a physical barrier against moisture loss and the entry of micro-organisms that cause rot. If the neck remains moist, it provides a pathway for decay organisms to enter the bulb.
The ideal environment for curing is warm, dry, and well-ventilated, with temperatures between 75°F and 80°F. The harvested onions should be spread out in a single layer on a screen or rack, protected from direct sunlight and rain, such as in a covered porch or a well-ventilated shed. This drying period usually lasts between one and three weeks, depending on the heat and humidity.
Curing is complete when the outer skins are papery and rustle when touched, and the neck is completely dry and tight. Once the neck is entirely dry, the tops should be trimmed, leaving a one-to-two-inch stub above the bulb. The roots should also be clipped close to the bulb at this time, completing the preparation for long-term preservation. Any bulbs with thick, soft necks or signs of bruising should be set aside for immediate use, as they will not store well.
Post-Cure Storage Methods
Once the onions are fully cured, they can be moved to their final long-term storage location. The goal is to maintain a cool temperature and low humidity to keep the bulbs dormant and prevent sprouting. Optimal storage conditions involve a temperature range of 32°F to 40°F and a relative humidity of 65% to 70%. Temperatures above 40°F encourage sprouting, while excessive humidity promotes root growth and decay.
Onions should be stored in containers that allow for excellent air circulation, such as mesh bags, old nylon stockings, or slatted crates. Braiding the dried tops is a traditional method that facilitates hanging and improves airflow around the bulbs. Avoid storing onions near potatoes or apples, as the ethylene gas released by these items can shorten the onion’s dormancy period.
The potential storage duration is heavily influenced by the variety planted. Pungent, long-day onions are bred for storage and can last for many months. Conversely, sweet, short-day varieties have a higher water content and thinner skins, meaning they typically only store well for a few weeks to a couple of months. Regular inspection of the stored bulbs is important, and any onion showing signs of softening or decay should be removed immediately to protect the rest of the supply.