The transition from a green, leafy plant to a firm, storable bulb requires precise timing when harvesting spring-planted onions. Knowing the exact moment to pull the bulbs from the soil is not just about maximizing size; it is a fundamental step that locks in flavor and dictates the onion’s potential for long-term storage. Harvesting too early means a smaller, more perishable bulb, while waiting too long risks the bulb beginning to rot or re-grow in the soil. The success of your entire growing season ultimately depends on recognizing the subtle visual cues that signal the plant has completed its underground work.
Identifying the Signs of Maturity
The most reliable sign that spring-planted onions are finished growing is the natural toppling of the green tops. This occurs because the neck, the transition point between the foliage and the bulb, softens and collapses as the plant redirects its energy into the bulb for final maturity. When about half to three-quarters of the tops have fallen over, the process of carbohydrate transfer from the leaves to the bulb is complete, and the onion is ready for harvest.
Allow the tops to yellow or brown before pulling, as this ensures the bulb has fully developed its layers and protective skin. At this stage, the neck should feel soft and no longer stiff, indicating that the connection between the leaves and the bulb is weakening. To encourage the outer skin to tighten and prepare the bulbs for storage, cease watering the onion patch about one to two weeks before the expected harvest date.
Executing the Harvest
Choose a dry, clear day for the harvest, as wet soil increases the risk of rot. The physical removal of the bulbs must be executed with gentleness because any bruise or nick on the surface can introduce pathogens and shorten storage life. Before pulling, use a garden fork or trowel to carefully loosen the soil around the bulbs, especially in compacted ground.
Once the soil is loosened, gently pull the onions up by their tops or, ideally, by the neck of the plant. Avoid grabbing the foliage and yanking forcefully, as this can cause the tops to rip off, leaving an open neck highly susceptible to moisture and rot. After lifting the bulbs, shake off any large clumps of soil, but avoid washing them with water, which would counteract the drying process.
Curing and Storing Your Harvest
Curing dries the outer layers and neck, creating a papery, protective seal for long-term preservation. Spread the freshly harvested onions in a single layer in a warm, dry, and well-ventilated location, such as a covered porch or a garage. The ideal temperature range for curing is between 75°F and 85°F, and the onions must be kept out of direct sunlight to prevent sunscald.
The curing period typically lasts from one to three weeks, depending on the ambient humidity and temperature. The onions are fully cured when the necks are completely dry, feel tight, and the outer skins have become thin and papery. Once cured, the roots can be trimmed close to the bulb, and the dried tops should be cut back to about one inch from the neck, though storage onions can also be braided with their tops intact.
For optimal long-term storage, cured onions require a cool, dark, and dry environment with temperatures ranging from 35°F to 40°F and low humidity. High humidity promotes sprouting, while warmer temperatures cause the bulbs to deteriorate more quickly. The best storage containers encourage air circulation, such as mesh bags, braided strings, or wire baskets, preventing moisture buildup and spoilage.