Fall-planted onions allow gardeners to anticipate an early summer harvest of mature bulbs. Successfully harvesting requires careful attention to the plant’s signals and a precise sequence of steps to ensure the bulbs cure properly for long-term storage. Defining the exact moment to lift the bulbs, followed by necessary pre-harvest and post-harvest procedures, is paramount for securing a quality yield.
Visual Indicators of Maturity
Determining the precise harvest time involves observing the physical changes in the foliage, which signal that the bulb has finished its primary growth cycle. The most definitive sign of maturity is the natural softening and collapse of the onion’s neck, the area just above the bulb where the leaves converge. This softening indicates that the transfer of carbohydrates from the leaves to the bulb has concluded, and the plant is preparing for dormancy.
This transition is confirmed when the green tops begin to yellow, brown, and flop over. Growers should look for 50 to 75 percent of the tops to be completely down before initiating the harvest. Waiting until the tops fall over naturally is important because this process allows the bulb to draw down remaining nutrients from the foliage, contributing to the final size and density.
Another indicator is the drying of the leaf sheaths, particularly the newest growth, often called the “last leaf.” Since each leaf corresponds to a protective ring layer within the bulb, the drying of the last leaf indicates that the protective layers are beginning to form and seal. Harvesting too early leaves the neck open and the bulb susceptible to rot during storage. Waiting too long after the tops have dried risks the bulb re-absorbing moisture from the soil, which can lead to cracking or premature sprouting.
Pre-Harvest Preparation and Digging
The primary pre-harvest action is stopping watering one to two weeks before the anticipated harvest date. This intentional drying period encourages the outer skin layers to thin, dry, and harden. Stopping irrigation prevents the mature bulb from retaining excess internal moisture, which is the primary cause of rot and poor storage quality.
Moisture control is essential for promoting the development of the papery outer layers, which serve as the bulb’s natural protective wrapper against pathogens and water loss. The soil should be noticeably dry at harvest time to facilitate a clean lift and minimize bruising. Harvesting on a dry, sunny day further aids in this initial drying process.
When removing the bulbs, care must be taken to avoid damage, which compromises the onion’s integrity and shelf life. Instead of pulling the bulbs directly by the tops, which can tear the neck and create an entry point for disease, use a garden fork to gently loosen the soil around the bulbs. Once the soil is loosened, the onions can be gently lifted by the neck or bulb. Any bruised or nicked bulbs should be set aside for immediate consumption, as they will not store well.
Curing Onions for Storage
Curing is a post-harvest process that dries the outer protective scales and seals the neck of the bulb. This step prepares the onion for long-term preservation by minimizing moisture loss and creating a barrier against pathogens. The ideal curing environment is a location that is warm, dry, and provides excellent air circulation, such as a covered porch, an open shed, or a well-ventilated garage.
The bulbs should be spread out in a single layer, often on screens or racks, and kept out of direct sunlight, which can scorch the outer layers. Curing temperatures should range between 75 and 80 degrees Fahrenheit to facilitate rapid drying. The curing period typically lasts for two to three weeks, though it may take longer in humid conditions.
Curing is complete when the necks are dry and tight, and the outer skins are papery and brittle. At this point, the dried tops and roots can be trimmed, leaving about an inch of the neck attached to the bulb, unless the tops are braided for storage. Properly cured onions should then be transferred to a cool, dark, and moderately dry storage area in mesh bags or hanging braids to ensure continued air circulation.