Proper harvesting and curing are necessary steps to maximize the storage life of homegrown onions. These methods transition the bulb from an actively growing plant part to a dormant, sealed food item, allowing it to maintain quality for months. Successfully storing onions depends on reading the signs of maturity and carefully managing the drying and sealing process. The goal is to create a papery, protective skin that prevents moisture loss and entry points for disease.
Knowing When to Harvest Onions
The timing of the onion harvest is determined by visual indicators that signal the plant has reached maturity. The primary sign is the natural yellowing and falling over, or “lodging,” of the green tops. When approximately 70 to 80% of the foliage has collapsed and started to dry, the onion is ready for lifting, as the plant has begun drawing energy back into the bulb.
Cease watering the onion patch one to two weeks before the expected harvest date to begin the necessary drying process while the bulb is still in the soil. This withholding of moisture encourages the outer skin layers to dry and tighten around the bulb. This preparatory drying strengthens the neck and helps prevent common storage issues like neck rot, which thrive on excess moisture.
The Physical Act of Harvesting
Once the tops have fallen, the bulb must be removed with great care to avoid bruising or cuts that could compromise the onion’s integrity during storage. Instead of pulling the plant by its dried top, use a garden fork or small hand trowel to gently loosen the soil around the bulb first. This technique minimizes the risk of tearing the neck or damaging the outer layers.
After lifting the onion, gently brush off any loose soil clinging to the bulb. Do not wash the onions at this stage, as introducing external moisture will counteract the preparatory drying and increase the chance of rot during curing. Any onions that appear damaged, bruised, or have a thick, still-green neck should be set aside for immediate use, as they will not store well long-term.
The Essential Curing Process
Curing is the post-harvest step that prepares the onion for long-term dormancy by sealing the bulb. The process rapidly dries the neck, which is the most vulnerable entry point for pathogenic fungi and bacteria, while simultaneously forming the characteristic papery outer scales. This dried outer skin serves as a protective barrier, minimizing moisture loss and protecting against microbial invasion.
Ideal curing requires a warm environment with high heat, low humidity, and continuous, excellent air circulation. Temperatures should be maintained between 75°F and 90°F, though the 80s are often cited as optimal for developing strong skin color. Spread the onions in a single layer on a rack or screen in a sheltered, dry location, such as a covered porch or well-ventilated barn, to ensure air circulates around each bulb.
The curing period typically lasts between two and four weeks, with the exact duration dependent on the temperature and relative humidity of the environment. A lower humidity level, ideally less than 60%, is preferred to hasten drying. Curing is complete when the neck of the onion is completely dry and tight, shriveled down to a thin, papery tube with no hint of green or moisture when pinched.
Post-Curing Preparation and Long-Term Storage
Once the onions are fully cured and the necks are dry and crisp, final preparation for storage can begin. Trim the shriveled roots close to the bulb with clippers, and cut back the dried tops, leaving a stem of about one to two inches attached to the bulb. Leaving this short stem maintains distance between the cut surface and the bulb, reducing the risk of rot organisms entering the interior.
Cured onions must be stored in a cool, dry, dark environment to maintain their dormancy and prevent sprouting or rooting. The optimal temperature range for long-term storage is between 35°F and 50°F, with a relative humidity around 65% to 70%. Storing onions in mesh bags, perforated crates, or by braiding the tops allows for continuous air circulation, which prevents condensation and subsequent mold growth. Store onions away from ethylene-producing items like apples and potatoes, as this gas can disrupt dormancy and encourage premature sprouting.