Proper water management is important for successful onion cultivation, particularly as the growing season concludes. Onions require consistent moisture throughout their bulbing phase, but the plant’s needs change dramatically near the end of its life cycle. The transition from active growth to harvest requires a deliberate cessation of irrigation. This period of water withdrawal initiates the maturation process within the bulb. Carefully managing the water supply at this specific time is directly linked to the bulb’s readiness for long-term storage.
Recognizing the Visual Signals
The most reliable indicator that it is time to stop watering is a noticeable change in the plant’s foliage. This signals that the onion has shifted its energy away from leaf production. This visual cue is known as lodging or “neck fall,” where the green tops soften and begin to fall over naturally. This physical transformation occurs when the transfer of carbohydrates from the leaves to the underground bulb has largely finished.
Gardeners should monitor the crop closely and cease watering when approximately 50 to 75 percent of the tops have collapsed and started to turn yellow or brown. Waiting until a high percentage of plants show this sign, often around 85 to 90 percent, ensures that most of the bulbs have reached peak maturity. The area where the leaves meet the bulb, known as the neck, will also begin to feel soft and narrow as the plant matures.
Stopping irrigation at this point allows the soil to dry out before the bulbs are removed from the ground. This drying period, typically lasting 7 to 14 days after the tops fall, is a crucial final stage of maturation. Continued watering after the tops have lodged negatively affects the bulb’s ability to cure properly and drastically reduces its potential storage life. The collapse of the foliage signals that the final growth phase is complete and harvest should begin shortly.
Preparing the Onion for Curing
The deliberate withholding of water in the final weeks of growth serves a distinct physiological purpose that directly prepares the onion for post-harvest handling and storage. Allowing the surrounding soil to dry out forces the plant to begin the process of senescence, or natural deterioration. This moisture reduction is what enables the critical sealing of the onion’s neck.
The neck is the most vulnerable entry point for moisture, fungi, and bacteria that can cause rot during storage. When irrigation is stopped, the fleshy, succulent tissue of the neck shrivels, dries, and forms a tight, papery seal. This natural closure acts as a barrier, protecting the inner layers of the bulb from pathogens. Watering after the tops have fallen introduces unwanted moisture into the soil, which can delay or prevent this vital neck sealing.
Moisture introduced at this late stage can lead to a condition known as a thick neck, where the top tissue remains soft and green. This makes the onion highly susceptible to molds like sour skin or black mold. Onions with thick necks will not store well and should be set aside for immediate consumption rather than long-term keeping. The dry, papery outer layers that form during this water-cessation period are responsible for the bulb’s ability to remain dormant and firm for many months.
Immediate Steps After Pulling
Once the foliage has dried and the soil is no longer saturated, the mature bulbs must be gently lifted from the ground to begin the curing process. Harvesting should be done carefully to prevent any bruising or nicking, as even minor damage can invite rot. Gardeners can use a garden fork to loosen the soil around the bulbs before gently pulling the onions up by their tops.
After removing the bulbs, the initial step is a short period of field drying, provided the weather remains dry and sunny. The onions can be laid directly on the soil surface for one to two days. To shield them from direct sun exposure, which can cause sunscald, drape the tops of one row over the bulbs of the next. If rain is expected, or to prevent sun damage in intense climates, the bulbs should be moved immediately to a protected area.
The more extensive curing process involves moving the onions to a location with warm temperatures, low humidity, and excellent air circulation. The onions should be spread out in a single layer, often on screens or racks, to ensure air flows around all sides of the bulb. This phase, lasting two to four weeks, completes the drying of the neck and the outer skins, which is necessary before trimming the roots and tops for final storage.
Curing Conditions
Ideal conditions for curing are:
- A temperature of approximately 75 to 80 degrees Fahrenheit.
- Low humidity.
- Excellent air circulation.
- A well-ventilated space, such as a covered porch or a shaded shed.