Onions are a great pick for the home gardener. They grow well in most parts of the U.S. and have many uses in the kitchen. You can grow them specifically for green onions or you can let them mature and harvest them for their large bulbs. You can also choose to grow onions and use a few early as green onions, harvesting the remainder as delicious bulb onions.
There are also special kinds of onions that don’t develop bulbs and that are used exclusively for green onions. Onions are a popular cool-season vegetable and although they are considered a biennial plant they are grown as annuals.
The onion is exceptional in that it will thrive under a very wide range of climatic and soil conditions. There is perhaps no extended area in the United States, except for the mountainous regions, where the onion cannot be successfully grown. However, onions grow best in temperate climates without great extremes of heat and cold.
Onions grow in an unusual manner. They start growing the large bulbs we know as onions when the levels of daylight reach an appropriate level for them to start forming. The time that you plant the onions affects when they form bulbs. If you plant your onions too late in the season, they may not form bulbs properly.
One important thing to remember about onions is that there are two different classes:long-day and short-day onions. Long-day onions are more appropriate for northern states because they are adapted to longer days. Southern states should use short-day varieties of onions. When you go to your nursery, they will usually list long-day onions as L and short-day onions as S.Short day onions develop bulbs with an average of about 12 hours of daylight. Long-day onions form bulbs with more sun, around 15-16 hours of daylight. You should grow the kind of onion appropriate for your region to ensure proper maturation of the onion bulbs. Keep reading for more information about long-day and short-day onions.
Harvesting Bulb Onions
Depending on the variety, bulb onions grown from transplants or sets will need about 3 months to reach maturity. Many onions are ready to pull up and harvest by late summer, roughly late July or early August.
In the Northern states onion bulbs are generally allowed to become as ripe as possible before harvest. Professional growers usually prefer that the tops ripen down and shrivel and that the outer skin of the bulbs be dry before the onions are removed from the soil. In the Southern states, where the onions are not cured so thoroughly, they are often pulled about the times that the tops begin to break and fall.
On farms, the ripening process may often be hastened by rolling a very light roller or barrel over the tops to break them down. This process is frequently spoken of as “barreling.”
Where the bulbs are practically on the surface they may be pulled by hand and thrown in windrows consisting of eight to ten onion rows.
In any case, it will be necessary to gather onions from the soil by hand. After lying in the windrows for several days and being moved around occasionally you can remove the tops by twisting them off or by using ordinary garden shears.
If the onion bulbs are considerably covered with soil it will be necessary to employ a cultivator for lifting them up from the soil. As the tops are removed the bulbs are generally placed in wooden crates or other containers for drying. You can learn about the best tools for harvesting onions and other vegetables.
Harvesting onions in the early morning is recommended. If the sun happens to be bright and hot on the day of harvest, try moving the onions to a shady part of your yard. Note that the stronger and hotter the sun, the greater chance there is of sunburn on the bulbs.
Many gardeners let the bulbs air dry in the same spot that they were harvested for a day after an early morning harvest. It’s best to let your onion bulbs dry out thoroughly before storing them. Do not expose the onions to morning dews.
Please note that too much exposure to the sun may injure the onion bulbs, so eventually, you’ll need to store them in a safe place. In some cases, a certain color is desirable for the onions, as is the case with the fancy White Globe onion, and these could be discolored or damaged by prolonged exposure to sun and rain. Therefore, it is necessary to cure them indoors to maximize their shape and color.
Another way to harvest is to start the curing process by partially removing the onions from the ground, leaving part of the bulb exposed. The onions will begin to dry out and cure while still in place. You should cure your onions for at least two weeks and in some cases, it is recommendable to cure them a full month.
You can then chop off the top of the onion with a sharp, clean knife or a pair of pruners. Leave just a little of the top part of the onion intact. As you cut the tops of the onions for storage, check for damage such as cuts and bruises on the main bulb. Also check for evidence of disease.
If the onions are stored too close together, there is the potential for the disease to spread from one onion to the next. Please see our troubleshooting guide to learn more about common diseases that affect onions and how to treat them.
Bolting occurs when your onions send up flower stalks. If you see flower stalks emerging from your onions, harvest them immediately. Unfortunately, onion bulbs will not grow any larger once they bolt. Another problem is that the flower stalk comes from the center of the onion bulb. Therefore, you should eat these onions quickly as they do not store well after bolting.
Harvesting Green Onions
In most cases, green onions are actually bulb onions that have not reached full maturity. You can grow green onions from most standard onion varieties. If you grow large batches of onions, you can actually harvest a few of your onions early as green onions and then let the rest form bulbs for a later harvest. This is a useful technique for thinning your onion plot as well.
There are some varieties of onions such as Beltsville Bunching that will actually not form bulbs and are used specifically for green onions. They form groups of thin root-like structures instead of bulbs. These are often referred to as bunching onions or scallions.
You can harvest green onions when the tops of the onions grow to about 5 inches high. The longer you let them grow, the more potent their flavor will be. Take into account that if you leave them for a long time the flavor may be too strong for salads, etc. You’re best to cook these onions rather than eating them raw.
You can harvest the green parts of the onions about a month after planting sets. Transplants will also provide green onions about a month after planting. Some onion varieties are better than others for growing green onions. Please see our list of recommended onions for the best ones to grow green onions.
Be warned that bolting, or when the plants start to produce flower stalks, can happen under certain circumstances when growing onions. In these cases, it’s best to pull out these plants as soon as possible and use the green onions. Unfortunately, you won’t be able to use these onions as bulb onions.
Ideal Growing Conditions for Onions
The essential requirements for a good soil for growing onions are plenty of organic material, sufficient drainage, and regular weeding. If a soil has the proper combination of sand and hummus and you can easily work it, it should hold moisture and nutrients well and should drain properly. Adding compost to your soil is a great idea and will always improve soil texture and drainage.
Sandy soils need to be worked with compost before growing onions for the first time. Break up the soil in the fall and work in the compost. If time permits, allow the soil to sit and plow again in the spring before planting your onion crop. Otherwise, you can break up the soil and add the compost just before planting in the spring. Just make sure the compost is fully decomposed. If you’re not sure how to compost correctly, please see this excellent compost guide from the University of Missouri Extension Center.
It is generally appropriate to grow onions where you have grown other crops before. In fact, if you’ve kept your garden weed-free, this can help improve the texture of your soil. Corn, beans, and potatoes are suitable crops with which to precede onions. Cowpeas are also excellent for conditioning the soil before planting a large crop of onions.
Onions generally should be rotated with other crops each season. If you’re growing a large batch of onions, try out a leguminous crop for use as green manure. Continuous cropping with onions in the same plot can attract pests and diseases to your garden over time.
The cultural requirements of onions are frequent shallow stirring of the soil and proper weeding. The feeding roots of the onion run close to the surface of the soil and should not be disturbed by deep cultivation. Sometimes a heavy rain after seeding will pack the surface so that the seeds can’t breakthrough. Under these circumstances, it may be necessary to slightly break up the soil with a steel rake or a rake-like attachment on a cultivator.
Mulching your onions after they start to form larger plants is an excellent way to retain soil moisture and keep weeds down in your vegetable garden.
In most cases, fertilizers aren’t really necessary to grow onions. A little compost added to the soil should be sufficient to grow a good onion crop. It is difficult to make the soil too rich for onions, provided that the compost is well decomposed and properly mixed in with the soil.
If you choose, an application of a natural or organic fertilizer during the growing period can also help your onions thrive without the potential hazards of using chemical fertilizers. Better yet, try out a natural Mycorrhizal fungi root-builder, which will help your plants make better use of the nutrients already found in the soil.
Whatever kind of fertilizer you decide to use, you should first educate yourself about the nutrient content of the product. Many gardeners over-fertilize their plants because they do not know what level of nutrients they need or how often to apply fertilizer. The nutrient content of fertilizers is reflected by the NPK number. NPK stands for Nitrogen, Phosphorous, and Potash (Potassium).
The onion does best under rather cool conditions, with lots of moisture during the early stages of growth. A thin layer of mulch can help to retain soil moisture. For proper ripening of the bulbs, they will need a reasonable degree of heat together with both dry soil and drier air.
After they start to mature, onions often do quite well with just rainwater, depending on the level of rainfall in your area. However, supplemental water may be necessary for drier areas. In general, you can water every 5-7 days during the initial growth period and during dry spells.
Weeds are often a problem with onion crops because they compete for nutrients. When you cultivate weeds, make sure to work only the top layer of soil or carefully pull out the weeds by hand. You may end up damaging the roots if you cultivate too deeply. Mulching your garden is an excellent way to keep weeds down in your vegetable garden. You can also consider a permeable weed barrier to reduce problems with weeds.
It is almost impossible to produce a crop of onions without a little hand weeding, especially after heavy rains. The work of hand weeding may be minimized by the use of specialty weeding tools.
Thinning is generally left until the time of the first-hand weeding when all thick bunches along the rows are thinned to a uniform stand of eight or ten plants to the foot. It is always a good idea, however, to allow for considerable loss of the plants, and unless the plants are so thick as to actually crowd, thinning won’t be entirely necessary.
There are several ways to grow onions. You can grow them from sets, seedlings (transplants), or seeds.
Growing Onions from Sets
Sets are defined as onion bulbs that have reached about one inch in diameter. These small bulbs are conditioned to be planted later in gardens. After planting them, they immediately grow to form larger onion bulbs, although sets are sometimes appropriate for growing both bulb onions and green onions.
Gardeners growing onions in a small garden plot are advised to try growing them in sets. Onions planted in sets grow very hardy and mature quickly for easy harvesting.
When you go to the nursery, you may see onion sets sold only by their color. White sets of onions are some of the best for green onions. Please see our list of onion varieties to get an idea of the best onions to grow from sets.
Buy your sets early in the growing season and if you’re not going to plant them right away you’ll need to store them somewhere cool and dry, preferably a dark garage or storage shed.
If you plan on growing green onions, break up the sets appropriately. Sets for green onions should be about ½ inch in diameter or more. The smaller sets will make the best bulb onions. The rounder sets grow flatter onions. Round onions typically come from longer, tube-shaped sets.
Plant the onion sets about 1 ¼ inch deep. Space the rows out about 16 inches apart. If you choose, you can plant the sets pretty close together in the rows. As they grow you can thin out the green onions and let the rest develop as bulbs.
Growing Onions from Transplants
Onion transplants (seedlings) are defined as small plants that have been growing for roughly two months. They have not yet formed bulbs. However, when planted at the correct time they work very well to form bulb onions.
Onions grown from seedlings are a good pick for growing larger bulb onions. You can get them from nurseries and on-line catalogs. Buying from your local nursery is generally less expensive than purchasing onions through catalogs as the shipping can be pretty pricey. Your local nursery should also have a better idea of what varieties of onion grow best in your area.
Remember to pick long-day varieties for northern states and short-day varieties if you live in a southern state. Please see our list of recommended onion varieties for a list of short and long-day onions that will work for your region.
Early April will work for planting onion transplants in most regions. Plant your transplant about 1 inch deep. You should place the transplants about 4 Â½ inches apart in your rows. This spacing will help you grow larger onion bulbs. About half this spacing will allow you to grow green onions. Space the rows about 16 inches apart. If you prefer to grow onions in garden beds instead of rows, give them about seven inches of space on all sides.
Growing Onions from Seed
If you grow onions from seeds planted directly into your garden, plant them about 3/8 of an inch deep and space your rows at least 1½ feet apart. In general, wide rows work very well for onions.
You can also sow seeds to transplant in a greenhouse, hotbed, cold frame, or specially prepared beds at the rate of 3½ or 4 pounds for each acre of land to be planted.
When the seeds are grown under a cover, they are typically easy to care for and provide with the proper water and ventilation. The seedlings need to be â€œhardenedâ€ before planting though.
When ready to transplant, the seedlings should be somewhat smaller than a lead pencil and rather stocky. Begin by exposing them gradually to cooler temperatures and a little less water.
The advantages gained by transplanting seedlings grown indoors are an earlier crop, a uniform stand, and bulbs of a more regular size. Where a small area of onions is to be grown, the transplanting method is ideal, but for large garden plots which may require more time and labor, transplanting seedlings may be impractical.
After transplanting, the seedlings will require rain or watering in order to start growing in the garden plot, so you may be limited in growing where you have ready access to irrigation.
To transplant, lift the onion seedlings from the seed bed and trim the roots and top a little. As soon as the plants are up and the rows can be followed, a cultivator can be used to break up the soil a little.
The most important factors for proper onion storage are good air circulation, relative dryness, and cool temperatures. Look for an appropriate area in your home that has these conditions. Store your onions in small quantities and make sure they are safe from freezing.
You should periodically inspect the onions for damage and disease. Be careful to use or discard any onions that show signs of problems. If you want to use the onions, simply cut away the infected area and use it within a few days. Onions that begin to feel soft to the touch may start to rot quickly. You may want to send these onions to the compost pile rather than using them.
In order to properly store onions, they must be well-ripened and cured. Those that are immature, soft, or thick-necked should never be placed in storage but used as soon as possible. Properly stored onions should be hard and may even rattle almost like wooden blocks when poured from one crate to another.
For the bulbs to remain bright and attractive, they should not be allowed to lie exposed to the weather but should be stored in cool, dry areas as soon as possible.
In handling onions it is a good idea to pass them over a screen to catch any of the loose skins and to remove any of the soft, decaying bulbs.
Another good option for storing onions is to tie them up in bunches and store them by hanging them upside down in a cool, dry place.
Note that the stronger flavored onions last longer in storage than the sweet onion varieties. Try using all your sweet onions no later than two months after placing them in storage.
Onion Troubleshooting Guide
Pink Root: Symptoms include onions that are underdeveloped and that have discolored roots. The roots often start to rot and have a pinkish tone. This disease is caused by a fungus in the soil. The fungus is usually brought home on young plants so make sure to inspect all onion sets and seedlings for evidence of discoloration on the roots. Look for onions certified against the pink root. PRR indicates pink root resistance. Rotate your crops frequently to avoid problems with this and other soil-borne diseases.
Rot: This problem occurs when onions rot quickly when placed in storage. Improper removal of the onion neck can expose your crop to fungal diseases growing in the soil. Make sure to remove the tops when they are completely dry. Letting the tops of the onions dry out completely after cutting will also help to prevent this problem. Do not store your onions too close together after harvest. You can also use a natural fungicide in the soil to prevent rot and other soil-borne diseases.
Purple Blotch: The symptoms of this fungal disease are a purplish discoloration on the leaves. This disease is not spread from the soil. It most often affects plants during extended periods of high moisture levels and it spreads from plant to plant through the air. This disease can cause stunted bulb growth and bulb rot when the plants are harvested and stored. Try an organic fungicide to counteract this problem.
Tip die-off: Symptoms of this fungal disease include browning tips which begin to rot and die off. Pink root causes similar symptoms. Alternaria is the fungus often responsible for this problem. You can deal with Tip die off by asking your nursery for resistant varieties. Also, check to see the soil conditions and your watering frequency. A well-draining soil is important to prevent this disease.
Thrips: Thrips are a common insect that attacks onion plants. Symptoms of thrips include graying leaves and the presence of tiny yellow to dark-colored insects. Try out a natural or organic insecticide to kill off thrips and other insects.
Root Maggots: Problems with root maggots often occur above 40 degrees north latitude. Root maggots cause rotting at the base of the onion. Beneficial nematodes are useful for controlling this problem. Please see this website from a professional extension agent for more information on root maggots.
Bent, Broken Onions: If the leaves of onions are accidentally bent over or crushed before the onion bulbs are properly formed, the bulbs may cease to grow. This will cause problems with storage. While you can still use these onions, they will not be of the best quality and are definitely not recommended for selling.
Bolting: Bolting occurs when your onions send up flower stalks. This is often caused by rapid changes in temperature. The change in temperature is a signal to the plant to go to seed, thus the onions begin to send up a flower stalk. If you see flower stalks emerging from your onions, harvest them immediately. Unfortunately, onion bulbs will not grow any larger once they bolt. Another problem is that the flower stalk comes from the center of the onion bulb. Therefore, you should eat these onions quickly as they do not store well after bolting. Pick the proper onion variety for your area and you should avoid most problems with bolting.
Recommended Kinds of Onions
When you go to your local nursery, you may be limited in what kinds of onions you can grow. Online nurseries and plant catalogs are a good option to buy more exotic kinds of onions. However, always make sure that the onion is appropriate for growing in your area. This will help reduce problems with bulbing, bolting, diseases, etc.
Please see our posts on different onion types for lots of great ideas on onion varieties for your garden.
Shallots are related to onions but have a different flavor. They also have ornamental value as they produce attractive flowers during the summer. They can grow quite tall as well, about 1 ½ foot. French shallots (grey shallots) are quite popular. There are also red shallots, echalion shallots, and Dutch yellow shallots.
Recommended Varieties for Green Onions
White Portugal onions are a great pick to make green onions. Other varieties for green onions include White Spear, Ebenezer, and Tokyo Long White.
These kinds of onions are appropriate for harvesting as green onions. Recommended varieties include Beltsville Bunching and Japanese Bunching. These onions work just as well if planted from seedlings, seeds, or sets. These kinds of onions are a good pick for colder climates and late fall to winter harvests. They will not form bulbs and indeed the entire plant with the root structure can be harvested and used.
These are onions that are planted during the winter in some areas and are harvested during the following growing season. Egyptian, Hill, and Walking Onions are often considered winter onions. They are good for an early batch of green onions. Make sure to use a layer of mulch with these kinds of onions. Cornell University has a great guide to growing Egyptian onions.
Disease Resistant Onions
‘Texas Grano 1015Y’ has good disease resistance. Crystal Wax is a disease-resistant white onion with a mild flavor. Use quickly after harvest.
Out of all the onion varieties out there, the white Bermuda onions keep about the least amount of time in storage. You can easily grow white Portugal from seed. Use this onion quickly after harvest.
Pungent yellow onions are the onions that work best for long storage. Yellow Globe and Copra are good picks for a long-storing yellow onion. Sweet Sandwich is a yellow hybrid onion that stores well. It grows as a long-day variety.
The large red onions are usually sweeter onions. They are good for eating raw or cooking. Burgundy is a delicious red onion. It has a milder flavor than other onions. Red Wethersfield is a good pick and comes as a long-day onion. This onion grows very well from sets.
Sweet onions are sometimes larger than their smaller cousins. Vidalia, Sweet Spanish, Bermuda, and Walla Walla are good picks for sweeter onions. White Bermuda has a great sweet taste but won’t keep for long in storage.
Early Yellow Globe is a popular yellow bulb onion and grows well in northern states. Grow the yellow Buffalo onion for an early harvest. The Ebenezer onion is either white or yellow. They grow very well from sets. White Portugal is an excellent option to grow by seed. Use this onion quickly after harvest. Yellow and White Spanish are popular onions for northern states. They produce large bulbs but have a later harvest. Sweet Sandwich is a yellow hybrid onion that stores well. Walla Walla Sweet is a popular long-day onion.
These onions do well in the southern states. Texas Grano is a good pick and has a nice, sweet flavor. Grano 1015Y is a good variety that stores well. Granex is very popular in the southern states. This is a tasty onion that comes in yellow, white, and red varieties. The yellow Granex stores very well. Granex is sometimes called the Vidalia onion. Burgundy is a delicious red onion. It has a milder flavor than other onions. Crystal Wax is a disease-resistant white onion with a mild flavor. Use quickly after harvest. The yellow Bermudas are very popular, but Bermuda also comes as white and red onions. The Vidalia Sweet onion is a hybrid of the Granex. Red Hamburger is a popular short-day onion.