Onions are ready to harvest when their green tops begin to fall over and the necks soften, a process growers call “tops down” or “neck fall.” The sweet spot for most home gardeners is when roughly 60 to 80 percent of the plants in a patch have flopped. Pulling them too early means thinner skins and shorter storage life; waiting too long invites rot and re-sprouting in the ground. But reading the signs correctly, and knowing what to do in the days before and after you lift the bulbs, makes the difference between onions that last for months and onions that turn to mush within weeks.
The Tops-Down Signal
The single most reliable harvest cue is what happens to the leaves. As an onion bulb finishes sizing up, the plant stops pushing energy into foliage and the neck, the narrow stem just above the bulb, weakens. The top keels over under its own weight. This is not a sign of disease or damage. It is the plant telling you it has finished growing. A New Zealand field study that harvested onions at five stages ranging from zero to four weeks after 50 percent leaf collapse confirmed that the traditional window of 60 to 80 percent tops down, followed by field curing, produced the best postharvest quality and the most successful storage outcomes.1New Zealand Journal of Crop and Horticultural Science. Effects of onion (Allium cepa) plant maturity at harvest and method of topping on bulb quality and incidence of rots in storage
Not every leaf falls at once, and not every plant in a bed matures on the same day. This is normal. Rather than watching one plant, you want to scan the whole planting. When you can see that most of the tops have folded and only a handful are still standing upright, the crop is in its harvest window. A few stubborn uprights can be gently bent over by hand to encourage the drying process, though this is optional and some growers prefer to leave them alone.
Does the Percentage of Tops Down Really Matter?
It matters more than most gardening advice lets on, especially if you plan to store onions rather than eat them right away. Research on Ethiopian onion varieties found that toppling at 90 percent neck fall reduced bulb sprouting in storage by about 43 percent compared with bulbs harvested at 70 percent neck fall without toppling. Even harvesting at 70 percent neck fall with toppling cut sprouting by roughly 23 percent over the control.2Scientific Reports. Influence of variety, toppling stage, and storage duration on postharvest quality and shelf life of onion (Allium cepa L.) in Bahir Dar Zuria district The practical takeaway is that patience pays. Waiting until the vast majority of tops have fallen gives the outer scales more time to dry and tighten around the bulb, forming the papery skin that shields against moisture loss and pathogens during storage.
If you grow several varieties, you will notice they do not all hit tops-down at the same time. Early-maturing cultivars can be a few weeks ahead of late-season storage types. Judge each variety separately rather than assuming the whole garden is ready because one row has flopped.
Other Signs to Look For
Tops down is the headline indicator, but a few supporting clues help confirm the timing:
- Neck feel: Squeeze the neck between your thumb and finger. A ready onion’s neck feels soft and hollow, not firm and full of moisture. If the neck is still stiff and green all the way through, the bulb is still actively growing.
- Outer skin color: The outer wrapper should be shifting toward the variety’s mature color, whether that is golden brown, deep red, or white. A shiny, translucent outer scale means the bulb has not finished drying.
- Root activity: Lift one test bulb gently. Roots on a mature onion look thin and dry. Thick, white, actively growing roots suggest the bulb still has growing to do.
- Bulb size relative to the neck: A mature onion has a pronounced bulge below a narrow neck. If the transition from neck to bulb is gradual or the neck is still thick relative to the bulb diameter, the onion has not finished filling out.
None of these signs alone is definitive. Used together with the tops-down count, they give you a reliable picture.
When to Stop Watering
This is where a lot of gardeners inadvertently sabotage their harvest. The instinct to keep watering until the day you pull onions is understandable but wrong. Research on irrigation timing in semi-arid onion fields found that late-season irrigation dramatically increased bacterial disease. In inoculated test plots, late irrigation pushed bacterial disease incidence from about 28 percent to over 51 percent in one year and from roughly 5 percent to 23 percent in another, all without improving yield or bulb size.3Agricultural Water Management. Reducing the risk of onion bacterial diseases through managing irrigation frequency and final irrigation timing The recommendation from that work is to make your last irrigation shortly after the final leaf has emerged from the neck and around the onset of tops down. After that point, additional water does not help the bulb grow but does create conditions bacteria love.
A separate study found that overhead irrigation during the field-curing period, the window between lifting and bringing onions into storage, increased the incidence of bacterial soft rot in stored bulbs.4New Zealand Journal of Crop and Horticultural Science. Effect of husbandry practices and water applications during field curing on the incidence of bacterial soft rot of onions in store In practical terms, this means you should also watch the weather forecast when planning your harvest day. If heavy rain is expected, either pull the onions and move them under cover, or wait until a dry spell to start.
How to Lift and Cure
Once you have decided the timing is right, the physical act of harvesting matters more than people think. Resist the urge to yank onions straight out of the ground by their tops. Pulling hard can snap the neck or tear the outer skin, both of which open the door to infection. Instead, loosen the soil around the bulbs with a garden fork, then lift gently. Research on direct harvesting with mechanical removal of foliage, essentially topping onions right at harvest, showed an increase in neck rot caused by Botrytis allii compared with methods that left the foliage attached during curing.5Plant Pathology. The effects of direct harvesting and drying systems on the incidence and control of neck rot (Botrytis allii) in onions In other words, leave the tops on while you cure. Cutting them off immediately removes the natural barrier the drying neck creates against pathogens working their way into the bulb.
Curing is the step between harvesting and storage. Lay onions out in a single layer in a warm, dry, well-ventilated spot out of direct rain. A covered porch, a garage with the door open, or a wire rack under a roof overhang all work well. The goal is to dry the outer skins and close off the neck. A controlled curing study found that five days at around 28°C and 65 percent relative humidity produced optimal results, increasing bulb hardness and reducing water activity, which translates to longer shelf life.6Journal of Food Composition and Analysis. Influence of controlled curing process on physico-chemical, nutritional, and bio-active composition of brown Spanish onion Most home gardeners will not be controlling humidity to the percentage point, but the principle stands: warm, dry air with good circulation for about a week. In cooler or more humid climates, you may need longer.
You know curing is complete when the outer skins rustle like paper, the neck is completely dry and tight, and the roots are wiry and brittle. At that point, trim the roots close to the base and cut the tops to about an inch above the bulb, or braid them if you want to hang your onions for storage.
Why the Neck Is the Weak Point
If there is one anatomical feature of an onion that determines how well it stores, it is the neck. The neck is the entry point for moisture and microorganisms. A study of microbial communities in rotting onion bulbs found that the neck region was the primary zone where fungal succession began. Healthy bulbs had almost no fungal presence except in the neck tissue, while mildly rotten bulbs showed a sharp spike in fungal diversity starting there.7PubMed Central. Microbial succession and tissue-specific restructuring of bacterial and fungal communities during post-harvest onion bulb rotting This is why so much of the harvest advice circles back to the same idea: get the neck dry and keep it dry. A thick, moist neck at harvest is a liability no amount of good storage conditions can fully overcome.
For the home gardener, this means paying extra attention to “thick-necked” bulbs at harvest time. These are onions whose necks never fully softened or collapsed. They can still be eaten fresh, but they are poor candidates for long-term storage. Set them aside for immediate use in the kitchen.
How Feeding Affects Harvest Timing
If your onions seem to be taking forever to mature, your fertilizing schedule might be part of the reason. A field experiment on nitrogen timing found that onion plants given all their nitrogen late in the growing season formed mature bulbs later than plants fertilized before sowing or split between an early and late application.8Journal of Experimental Botany. Effects of Nitrogen Supply on Bulb Development in Onion Allium cepa L. Nitrogen encourages leafy growth, and as long as the plant is making new leaves, it is not focused on bulbing. The practical rule of thumb is to front-load your feeding. Give onions a good start with nitrogen-rich soil or fertilizer at planting and taper off by midsummer. If you are still adding high-nitrogen feeds in July or August (in the Northern Hemisphere), you are likely pushing your harvest date later and potentially into wetter, cooler weather that complicates curing.
What Happens If You Harvest Too Early
Pulling onions before the neck has properly weakened means the outer skins have not had time to mature. The bulbs will feel firm and look healthy, but the wrappers will be thin, tightly clinging, and more translucent than papery. These bulbs lose moisture faster in storage and are more vulnerable to physical damage. The skin simply has not had time to form an effective barrier.
Early-harvested onions also tend to have higher moisture content in the neck, which as discussed above is the primary entry point for rot organisms. You can still eat them, and they will taste perfectly fine, but expect a storage life measured in weeks rather than months. If you need to harvest early because of incoming severe weather, move the bulbs to a warm, well-ventilated curing area and give them extra drying time to compensate.
What Happens If You Wait Too Long
Leaving onions in the ground well past full maturity invites a different set of problems. Overexposure to soil moisture can restart root growth, and the bulbs may begin breaking dormancy. Inside a resting onion bulb, complex sugars called fructans accumulate and help keep the bulb dormant. Before a bulb sprouts, these fructans redistribute within the bulb, concentrating in the base plate. Researchers have identified this redistribution pattern as a marker that dormancy is about to break.9PubMed Central. Fructans redistribution prior to sprouting in stored onion bulbs is a potential marker for dormancy break Once the bulb decides to sprout, you cannot reverse the process. An onion that has begun sending up a new green shoot is using its stored energy for growth, which means the flesh becomes soft and hollow from the center outward. It is still edible, but the texture and flavor decline rapidly.
Overly mature bulbs also risk splitting, where the outer scales crack open, exposing inner layers to soil organisms. And in wet seasons, leaving mature onions in the ground for extra weeks is essentially giving bacterial and fungal pathogens more time to colonize the neck while it sits in damp soil.
Timing Differs by Onion Type
Not all onions follow the same calendar. The harvest window depends heavily on what kind of onion you planted and when you planted it.
- Long-day onions: Planted in early spring in northern climates, these typically mature in mid to late summer. They form bulbs in response to the long days of June and July and are usually ready between July and September depending on variety and latitude.
- Short-day onions: Planted in fall in mild-winter regions, these bulb up in spring and are often harvested by late spring or early summer. They tend to have higher water content and store for a shorter period.
- Intermediate-day onions: These fall in between and are common in the middle latitudes. Harvest timing varies but usually lands in summer.
Scallions and bunching onions are a different category entirely. They are harvested for their green tops and immature shanks, and the tops-down signal does not apply. You pick them whenever they reach a size you like.
Sweet Onions and Storage Onions
Sweet onions like Vidalia, Walla Walla, and Maui types have high water content and low sulfur compounds. These traits make them mild and delicious but also mean they do not store well regardless of how carefully you harvest and cure. Even with perfect timing and curing, a sweet onion may only keep for a few weeks before softening. Plan to use them quickly after harvest.
Storage onions, typically pungent yellow or red varieties, have more dry matter and more of the sulfur compounds that make your eyes water. Those same compounds act as natural antimicrobials, which is part of why pungent onions outlast sweet ones in the pantry. Researchers have been developing non-destructive tools, including handheld near-infrared spectrometers, that can measure dry matter and soluble solids content in the field with high accuracy.10Postharvest Biology and Technology. Nondestructive determination of dry matter and soluble solids content in dehydrator onions and garlic using a handheld visible and near infrared instrument That technology is aimed at commercial growers for now, but it underscores the point: dry matter content is the single best predictor of how well an onion will keep. The more dry matter, the better the storage potential.
Storing After a Good Harvest
Once your onions are fully cured, store them somewhere cool, dry, and dark with decent airflow. A basement, unheated garage, or pantry works for most people. Mesh bags, old pantyhose with knots between bulbs, or open crates all allow air to circulate. Avoid sealed plastic bags or airtight containers, which trap moisture and accelerate rot.
Ideal storage temperature for long-keeping onions is between 0 and 4°C with low humidity, roughly refrigerator conditions. At room temperature, you can expect several weeks to a couple of months depending on variety and how well you cured them. Check stored onions periodically and remove any that show soft spots, sprouting, or an off smell. One rotting bulb can spread pathogens to its neighbors quickly, especially if they are touching.
Avoid storing onions near potatoes. Potatoes release moisture and ethylene gas as they age, which can encourage onion sprouting. A separate shelf or opposite corner of the storage area is usually enough distance.
Green Onion Tops After Harvest
A common question after harvest is what to do with the dried tops once curing is done. If you are not braiding them for hanging storage, simply trim them off about an inch above the bulb and compost them, provided your compost pile heats up enough to break down any lingering disease organisms. If you had issues with downy mildew, white rot, or neck rot during the growing season, it is safer to bag the foliage and dispose of it rather than returning it to the garden ecosystem. Those pathogens can survive in soil and plant debris and reinfect next year’s allium crop.
For gardeners growing onions in beds that will be rotated, keep alliums out of that spot for at least two to three years. Soil-borne onion diseases build up with repeated planting in the same location, and rotation is the simplest defense. If you are working with raised beds or limited space where rotation is difficult, cleaning up all crop debris promptly after harvest becomes even more important.