When and How to Harvest Onions

Onions are great crops to grow because you can harvest them whenever you want—thin the seedlings and use them like scallions or wait until the plants stop growing for mature onions. But how do you know when an onion plant stops growing? That’s a good question; just read on for the answer.

Harvesting Onions

When onions are finished growing the leaves turn yellow, starting with the lower leaves. Then the stalks start falling over, putting a final end to the growth. If you want to use onions right away, go ahead and pick some. But if you plan to store them to use later, you better leave the plants in the ground for 10-14 days to cure.

Curing Onions

The next step is to pull the onions up (preferably on a sunny day) and let them rest on top of the soil for a day or two until the roots dry up. Cutting off the leaves is optional, but if you do, leave an inch of stem above the bulb to prevent rot.

Now your onions are ready for the second round of curing. Spread them out in a warm, well-ventilated place out of the sun—a porch is great—for a couple of weeks. The dryer the air the shorter the time needed for curing. When the onions look like the ones you get in the market, with dry paper-thin skins, put them in mesh bags and dry them some more.

The dryer they are the better they’ll get through the winter in a cool, moderately dry, airy space like a root cellar.

Of course, not all onions are grown for their bulbs. The roots and leaves of bunching onions can be harvested at any time during the growing cycle—the earlier the harvest the milder the taste. Scallions are perfect when they are six inches high.

That’s about all there is to harvesting onions.

Common Questions and Answers About How to Grow Onions

Can I freeze onions?

Though onions stay fresh for a long time, there are situations in which you may need to freeze some to use at a later time. Wash, peel, and chop your fully mature onions into half inch pieces and place them in freezer bags for optimal quality and odor protection. There is no need to blanch your chopped onions before freezing them. Properly prepared and stored onions should last approximately one year in the freezer before quality starts to deteriorate, though they will still be safe to eat long after one year has passed.

For most recipes, frozen onions can be used with little or no thawing necessary. Frozen onions work best in cooked dishes, however, frozen onions are not very good for caramelizing, as there is too much ice inside of them to caramelize properly. If you just want to get your onions soft enough to eat, frozen is fine, and they work well in soups and stews too. If you are making a stir fry though, or any other high heat dish, you would do better using fresh onions instead of frozen.

Can I grow onions in a grow bag?

Smaller onion varieties or green onions will grow well in a grow bag. Larger onion varieties will not work as well in grow bags because the bags do not provide a lot of soil depth and onions grow and develop beneath the soil. Grow bags do provide enough surface area required for a decent size onion crop. Grow bags can be purchased at your local nursery or garden center, or you can turn any bag of potting soil into a grow bag.

Can I grow onions in summer?

Onions can be grown over the summer and harvested as summer ends. You can plant onions in the late summer or fall in mild to warm climate regions for a spring harvest. The long day onion cultivars perform better when grown in colder climates.

Can I plant an onion from the grocery store?

Grocery store onions may have been treated for better storage, rendering them unsuitable for replanting. If you want to grow an onion from planting an onion, we recommend sourcing your onions from organic farms, or from your own garden. We also recommend growing onions using onion sets instead of seeds or seedlings. Still, it is possible to grow an onion from a grocery store onion. Since it takes two seasons to grow bulb onions from seed, growing onions from another onion is certainly a more time efficient method of onion cultivation.

If you have an onion on hand, you don’t need to grow them from a seed. Simply chop the bottom of an onion off and plant it in soil and you can grow your own onions from cuttings. With a little bit of TLC and a whole lot of water and time, you can grow an onion

Can I replant small onions?

Not only can you replant small, sprouted onions, it’s a recommended growing method otherwise known as onion sets. Onion sets are just small onions which have been harvested and cured to suspend their growth until they are replanted.

Can I use tomato feed on onions?

Onions do not need a fertile soil. Fertile soils promote top growth and onions need bulb growth instead, which is encouraged by a potash feed. Potash feeds like Tomato feed or comfrey tea are viable ways to feed your onion plants and encourage more bulb growth.

Can you eat onions straight from the garden?

Onions can be harvested and eaten at any stage and are especially good when eaten straight from the garden. It is a common misconception that you have to cure onions before eating them. Curing is a process that takes around one month, which is done to help preserve them and make them last longer when stored. You only need to cure onions that you want to store to use at a later date.

Can you eat the top of onions?

The green tops of sprouting onions are edible, and have a flavor similar to scallions or green onions, only slightly milder. If you are growing onions that have the long green shoots still attached, don’t throw the greens away. These onion tops have a pleasant, mild onion flavor and can be used in the same way that you would traditionally use scallions.

Can you grow onions in potting soil?

Onion seeds, sets, and seedlings all grow well in potting soil. If you place a small, whole onion in potting soil in a container, it will sprout new growth. Onions will grow in just about any type of soil, from sandy loams to clay-heavy mediums. The soil should be firm and well draining for best results. To amend soils that are too compacted or heavy and to help with moisture retention, mix in some organic compost or manure.

Can you grow onions in the same place every year?

Onions can be grown in the same ground year after year, however, doing so can encourage diseases that can affect your onion crops. Crop rotation is recommended when growing onions, meaning you should move the locations where you cultivate onions every year. Onions should not be planted in the same location more than once every three to four years. Practicing regular crop rotation can save you a lot of trouble when it comes to managing soil-borne pests and diseases.

Can you hang onions to cure?

To cure onions, hang them in bunches or spread them out on a rack, whichever method makes the most sense to you. Let your onions dry for two to three weeks. Once dry, the tops and necks of the onions will be dry to the touch and the outer skin will appear shrunken and papery. If you plan to braid your onions together for storage, leave the leaves intact.

Can you leave onions in the ground over winter?

If you leave a mature onion in the ground over the winter instead of harvesting it as recommended, the mature onion will begin to multiply. The onion that is left in the ground will begin to form sections, much like a garlic clove. Those sections can then be separated and planted as sets each spring.

Do bunching onions multiply?

Bunching onions are also known as true scallions, as they make no bulb, but they do multiply, without being invasive. There are many different varieties of bunching onions. There are a few different varieties, each type acts a little different but all have similar basic characteristics.

Do onions like manure?

Onion and garlic both enjoy fertile soils but neither needs very much nitrogen. Nitrogen promotes more top growth, which will encourage your onions to produce more stem and foliage growth instead of bulb growth, which is what you want to encourage. Avoid growing onions and garlic in freshly manured soil for this reason. Alternatively, dig over and manure the ground, tilling it and amending it several months before planting.

Do onions multiply?

Multiplier onions are a variety of onion that multiplies, allowing growers to harvest up to ten onions from a single plant, though they more commonly produce five to seven onions on average. Instead of planting them in the spring like most onion varieties, multiplier onions are planted in the fall and are ready to harvest well before spring planted onions.

Do onions need a lot of nitrogen?

Onions have moderate nitrogen requirements, but nitrogen fertilization is still very important to growing good onions because onions typically have weak, shallow root systems. Though decaying organic matter will provide some nitrogen, fertilization will still be necessary to get the most out of your onion crop. When it comes to choosing the right fertilizer for your onion crops, you should mainly focus on the N-P-K ratio, or the percentage of nitrogen, phosphorus, and potassium in the fertilizer product. For onion crops, you should select fertilizer mixtures with higher nitrogen levels. Nitrogen will improve bulb quality and boost storability and disease resistance. For most garden soils, a nitrogen-based fertilizer or a balanced fertilizer with an N-P-K ratio of 16-6-4 will work the best.

Do onions need a lot of water?

Onions are heavy drinkers and they do need a lot of water to develop big, healthy bulbs, however, the soil that you grow your onions in should be moist at all times, but never soggy. Water your onions deeply once per week instead of a light watering every day. Onions need plenty of water to produce high yields, but too much water will lead to disease and rot. To avoid overwatering, give your onions about one inch of water everytime you irrigate. Use your finger to gauge whether or not your onions need watering by sticking it down into the soil. If you can’t feel any moisture up to your first knuckle, it’s time to water your onion plants. When the top of the bed is completely darkened by moisture, you have provided enough water for your onion plants. Typically, onions need watering no more than once or twice per week.

Do onions need a lot of sun?

Onions require abundant sunlight to thrive and mature at a quick pace. Onion plants prefer full sunlight exposure but will tolerate partial shade, though the more shade they recieve, the slower they will mature, and the more susceptible they will be to pests and disease. Onions are unable to grow in full shade.

Do onions need potash?

Like all plants, onions need potash to develop healthy bulbs. The more potash available in the soil, the less sulphur your onions will absorb. For smaller, stronger tasting onions, use a low potash fertilizer. For larger, less potent onions, use a high potash fertilizer. Potash fertilizers provide your onion plants with the key nutrient potassium. Potassium improves the overall health of onion plants, improves their drought resistance capability, extends shelf life and boosts the overall yield.

Potassium levels in your soil also have an effect on your onion’s bulb firmness and size. Sufficient amounts of potassium in the soil will help your onions by improving their water use through regulation of transpiration and photosynthesis, increasing protein production, enhancing nitrogen use, and boosting overall plant health, including resistance to drought, pests, and diseases.

Do onions need to cure before eating?

Onions can be eaten at any time during their growth cycle. You only need to cure onions that you are planning on storing for extended periods of time. Curing is a month-long drying process that prepares your onions for storage by lowering the moisture level inside the bulbs. Fresh onions pulled straight from the garden are more crisp, juicy, and flavorful. If you have a batch of onions that are particularly pungent, curing might help soften the flavor a bit, but otherwise, there is no reason to cure onions before eating them.

Do onions spread?

When left in the ground, the onion plant will spread once new offsets form and develop. Onions are tunicate bulbs which grow by forming concentric layers that surround a central core. As the onions develop, offset bulbs grow from the base of the bulb of the parent plant beneath the soil. As new offsets are produced, the onion plant spreads out into the surrounding area.

How deep should a raised bed be for onions?

Raised beds for onion crops need to be six to eight inches deep in order to allow enough room for onion bulbs to fully develop beneath the soil.

How do you fertilize onions organically?

To provide the nutrients that your onions will need throughout the growing season organically, work in several inches of compost or aged manure at planting time and feed every two to three weeks after planting with a balanced organic fertilizer or compost on top of the original fertilizer trench at the rate of one half a cup per ten feet of row and then water thoroughly. Stop fertilizing when the onions start to bulb.

How do you grow onions in water?

Though you cannot grow onions from start to finish in water, as they do require the essential nutrients that they get from being planted in soil, you can get onions to grow root tips in just a glass of water and then you can move them into soil to grow. The process of getting onions to develop root tips in water is actually quite easy as well.

Simply place the onions in a clear glass or jar with the root ends down and add just enough water to the bottom of the glass container to cover the roots at the bottom of the bulbs. Place the glass in a windowsill that gets lots of sunlight all throughout the day and change the water daily. Roots will sprout up in no time.

How do you regrow onions in water?

Though it is impossible to grow onions from start to finish in water, because like every other plant, onions require the essential nutrients that they pull from the soil. However, you can get onions to grow root tips using only a glass of water. After the new roots develop,  you can move them into soil to cultivate another onion in just a few short months. The process of getting onions to develop root tips in water is actually quite simple to follow.

All you need to do is place your onion (or onions) in a clear glass or jar with the root end down and add just enough water to the bottom of the glass container to cover the roots at the bottom of the bulb. Place the glass in a windowsill that gets lots of sunlight all throughout the day and be sure to refresh the water daily. That’s all folks. Follow these easy steps and your onions will be sprouting new roots in no time.

How do you store cut onions in the refrigerator?

Cut onions will last in the fridge for up to 10 days. Wrap them tightly in plastic wrap or place them in a resealable bag. For longer storage time, place cut onions in the freezer in a freezer bag or airtight container to store for three to six months.

How do you trim an onion?

When your onion tops get to be about five inches tall, it’s time for a haircut. Trim them back to one and one half inch and save and eat the trimmings. Onion trimmings are very tasty, so don’t just throw them out. Toss them in an omelet or stir-fry, or add them to a quiche.

Trimming back your onion plants will force your onion plants to focus more energy on the roots, which will help your plants produce healthy, larger onion bulbs. Also, onion tops grow back surprisingly quick. You will probably be able to trim your onion plants back several times during a growing season.

How long do onions take to grow?

Standard dry bulb onions take a bit of patience on behalf of the grower, as they can take 100 to 175 days to reach full maturity. Green onions give gardeners more of an instant satisfaction, maturing from seed in just 20 to 30 days.

How long do you leave onions to dry out?

Onions need to dry out in the sun for two to three days and then continue to cure indoors for an additional two to three weeks. The entire drying (or curing) process should take about one month.

How many onions do you get from one plant?

Typical onion plants produce one onion per plant, so plant however many plants you need to produce the amount of onions that you typically use in a year.
If you are growing multiplying onions, however, you can get quite a few onions per plant, and if you leave some in the ground, you will have even more for your next harvest. Unfortunately, multiplier onions are quite small and even a large harvest of multiplier onions won’t add up to a couple of large bulbs produced by typical single onion producing onion plants.

How much soil do onions need?

If you are growing onions in a garden bed, provide a fertile, well-draining, loosely compacted potting soil at least six to eight inches deep. In a container, it is best to allow onions at least 12 inches of soil depth. When planting onion transplants, space plants out five to six inches apart in rows 12 to 18 inches apart. When planting onion sets, space sets out two to six inches apart and plant your sets no more than one inch beneath the soil.

How often do onions need to be watered?

Onions typically need one inch of water per week. Increase watering to two or three inches in especially dry weather or drought, or if you desire sweeter tasting onions. Instead of worrying about the frequency that you need to provide onions with water, focus on the moisture level of the soil that they grow in. Check the soil frequently by sticking a finger into it. If it is dry down to your first knuckle, it is time to give your onions a deep drink. Water deeply once per week instead of lightly every day, as onions prefer moist, but not soggy soil conditions.

How tall do onion plants grow?

The majority of the onion plant, and therefore, onion growth, is beneath the surface of the soil. However, after germination, onion tops grow pretty quickly. Once they sprout up to five inches high, trim them back to two inches to keep the plant focused on root growth and bulb development. Don’t just toss out your trimmings either, as they are quite tasty in a variety of savory dishes.

Is growing onions easy?

Growing, harvesting, curing, and storing onions can be a complicated and involved task, but if you know what to do, it is pretty easy to care for and cultivate onion plants. Generally, onions are considered to be easy to grow because of their hardiness, but knowing how to grow big, high-quality bulbs can take a bit of practice.

Should I cut onion flowers off?

A general rule to onion cultivation is not to let onion plants flower. If you see an onion plant has developed a bud, snip the bud off immediately to keep the bulb from splitting, and immediately harvest and eat those onions first, and don’t wait around too long to do so, as onions that have bolted generally do not store very well. If you can’t eat them immediately, cure them immediately, and try to use them up within a couple of months. Don’t stress out about a blooming onion too much though, as onion bolting is a problem even for professional onion growers. If a couple of your onion plants happen to flower, it’s not the end of the world. Bolted onions are still edible, and though cutting the flower stalk won’t restart bulb development, you can still harvest the bulb and put it to use even though it didn’t get a chance to fully develop.

Should onions be hilled?

If you are growing green onions, you can hill the soil slightly around your green onion plants to encourage development of long white stems. However, if you are growing standard bulb onions, especially if you intend to store your crop, do not hill your onions, even if they push the soil back and part of the bulb emerges from the ground, as hilling onions meant for storage could cause the necks of the onion to rot prematurely.

What do I feed an onion?

Onions need to be fed a steady supply of nitrogen to produce big bulbs. Side dress growing plants in early and mid summer with a half cup of a nitrogen-based fertilizer. If you have an alkaline heavy soil, use ammonium sulphate, which will slightly lower the soil pH. If you have an acidic heavy soil, use ammonium nitrate, which will raise the soil pH.

What do onions look like when ready to harvest?

Onions are ready for harvest when the bulbs are large and the tops turn yellow and start to flop over. When most of your onion crop is beginning to flop over, it’s time to pull up your bulbs and start the curing process.

What is an onion set?

An onion set is a small, dry onion bulb that was grown from seed last planting season but not allowed to fully mature. Onion sets are used to grow onions quicker than having to wait an extra season to grow onions from seed but sets don’t produce nearly as large of bulbs as onion seeds do.

What is the best fertilizer for growing onions?

Onions perform best when given a nitrogen-based fertilizer. Provide ammonium sulphate if your soil’s pH is alkaline and ammonium nitrate if your soil’s pH is acidic.

What month do you harvest onions?

By the middle of summer, onion bulbs start to plump up and gardeners can begin harvesting onions as needed. In the late summer or early fall, depending on your region, the onion stalks will begin to fall over, bending at the neck. This is a sign of the end of maturation and a signal that your onions are ready for harvest.

What month is best to plant onions?

In cold climate regions, onions can be planted as soon as the ground can be worked in the spring. In warmer climate areas, onions can be planted in the late fall or winter and will remain dormant during the winter, but will be ready to grow profusely as soon as the spring comes around.

What nutrients do onions need?

Onions need a long list of nutrients, but the most important one is nitrogen. To maximize growth and yield, nitrogen is the nutrient needed in the greatest quantities. Following nitrogen, the most important nutrients for onion plants are calcium, sulphur, phosphorus and potassium. Of the macronutrients that onions need to thrive, the most important ones are Boron, Copper, Iron, and Zinc.

Why are my onions flowering?

When an onion plant sends out a flower stalk, it means that the plant is under stress. The most common reasons why onion plants start to bolt are temperature fluctuations, cold-weather stress, loose soil, and over-fertilization. Bolting is a survival response. Abnormal growing conditions make the plant think that it’s dying, so it stops focusing on growing and maturing the bulb and begins focusing its energy on flowering.

Why are my onions so small?

The most common reason why gardeners end up with small onions is because they were growing the wrong type of onion for their climate zone.

Why do onion stalks fall over?

As the bulb maturation process nears its end, the necks begin to soften and the weight of the leaves cause the tops to fall over. This is usually a sign that your onions have ended their growing cycle. When 80 to 90% of your onion plants have fallen over, it’s time to harvest your onions. Very rarely, stalks can fall over due to wind damage, so check and make sure that your onion plant is not damaged before deciding to harvest your entire crop.

Want more information on harvesting onions?

Find more tips from the experts at these websites:

Harvesting Onions by National Gardening Association Editors.

Home Gardening: Growing Onions. PDF from Alabama Cooperative Extension System

Lynne Lamstein gardens in Maine and Florida and is currently working on a sustainable landscape. She has a degree in ornamental horticulture from Temple University.