Preserving a homegrown onion harvest requires precise timing and careful post-harvest treatment. Onions signal their readiness for storage with distinct visual changes, and ignoring these cues leads to rapid spoilage. Maximizing the bulb’s natural dormancy period requires harvesting at peak maturity and preparing the onion to seal out moisture and disease.
Visual Cues for Optimal Timing
The most reliable signal that onions are ready for harvest is the natural collapse of the plant’s neck. This neck is where the leafy top meets the bulb; as the plant matures, this tissue softens, causing the green tops to flop over. This “neck collapse” signifies that the transfer of carbohydrates from the leaves to the bulb is complete and growth has ceased. Harvesting for long-term storage should begin when approximately 50 to 80% of the onion tops have fallen over.
Waiting until nearly all tops are down increases the risk of rot or splitting in the field, which compromises storage life. The foliage will also start to turn yellow or brown and dry out, signaling the end of the growth cycle. A soft, limber neck indicates maturity, while a stiff neck means the bulb is still actively growing. Once these signs appear, the window for harvest is short, usually one to two weeks, before the bulbs become susceptible to decay in the soil.
The Physical Harvest Process
Proper harvest technique is crucial because any bruising or damage to the bulb creates an entry point for pathogens that cause storage rot. About one to two weeks before the expected harvest date, stop all irrigation to allow the soil to dry out. A drier environment helps the outer skin begin the necessary drying process and reduces the risk of post-harvest disease. Onions should always be lifted on a dry, sunny day.
Avoid pulling the onion directly by the tops, which can tear the neck and damage the bulb. Instead, gently loosen the soil around the bulbs first using a garden fork or spade inserted a few inches away. Carefully lift the soil and sever the roots underneath. Once loosened, gently pull the bulb from the ground by its neck, brush off any large clumps of dirt, and avoid washing the bulbs, as water promotes rot.
Curing: Essential Post-Harvest Treatment
Curing is a mandatory post-harvest treatment that prepares the onion for long dormancy by drying the outer layers and sealing the neck. This process creates a protective, papery barrier that locks moisture out and prevents the entry of rot-causing microorganisms. Ideal curing requires a warm, dry, and well-ventilated area, protected from direct rain and sun. Temperatures should range between 75 and 85°F; a covered porch, garage, or shed with good airflow works well.
Spread the onions out in a single layer on a screen or rack to ensure air circulates around each bulb. Curing generally takes between two and four weeks, depending on the environment. Curing is complete when the outer skins are fully papery, the neck is tight and completely dry, and the roots are brittle. Onions with thick or green necks have not cured sufficiently and should be used quickly rather than stored long-term.
Storing Onions Through Winter
For long-term preservation, cured onions require an environment that maintains cool temperatures and low humidity to prevent sprouting and decay. The optimal storage temperature is 32 to 40°F, which halts the bulb’s metabolism. Humidity should be kept moderately low, ideally between 65 and 70%, which prevents excessive weight loss while inhibiting disease growth. Storing the bulbs in a dark location is also important, as light encourages premature sprouting.
Proper ventilation is paramount to prevent moisture buildup that leads to fungal infections. Onions should be stored in mesh bags, braided into strings, or placed in shallow crates or baskets to maximize air circulation. Avoid storing them in plastic bags or next to moisture-releasing produce like potatoes, as this traps humidity and accelerates spoilage. Regularly inspect the stored bulbs throughout the winter, immediately removing any that show signs of softness, mold, or sprouting.