Onion, Bulb Onion

Allium cepa

Bulb onions are cool-season biennials usually grown as annuals. They are closely related to garlic, scallions (also called evergreen bunching onions and green onions), leeks, chives, shallots, and elephant garlic, all members of the Allium genus, which also includes hundreds of species and varieties grown as ornamentals. Onions are more closely related to turfgrass, palm trees, and orchids than they are to most garden vegetables. Onion relatives in the Amaryllidaceae family include Amaryllis and Clivia.

Onion varieties

Bulb onions are classified in many different ways, including:

1) by day length, which is the number of daylight hours needed for a given variety to initiate bulb formation (short-day, intermediate-day, long-day, or neutral-day), an important aspect for home gardeners;

2) by taste (American, with a strong, spicy-hot flavor; and European, with mild or sweet flavor);

3) by bulb color (yellow, brown, red, and white);

4) by market and cooking use use (green, fresh bulb, or dehydrator bulb); and

5) by storage length and quality (pungent varieties with thicker skins that store well, including many yellow varieties, versus generally mild and sweet onions that don't store well and are better for fresh eating).

The onion is believed to have originated in what is now Central Asia, West Pakistan, or Iran. It has been cultivated for more than 5,000 years not only as a food source, but also for art, religious, cultural, and medicinal uses. It appears frequently in ancient Egyptian art, and Egyptian political leaders took oaths of office while holding an onion in their right hand. During the Middle Ages in Europe, onions were used to treat various health ailments, as rental payments, or given as wedding gifts. Siberians used onions as a form of currency.

Research shows that onions may offer many health benefits. Its sulfur-containing compounds produce its pungent odor; studies and trials show that these compounds have been found to lower blood sugar by triggering insulin production. Other possible health benefits of onions include lowering cholesterol and triglycerides in the blood, improving cell-membrane function in red blood cells, supporting the liver in processing toxins, and supporting healthy bones and connective tissues.

Sun/Shade Needs (4)
Watering Needs once Established (4)
Heat Tolerance (2)
Frost Tolerance (3)
Price (1)

Recommended Varieties/Cultivars

Careful selection is critical to match bulb onion variety to day length, or hours of sunlight during your growing season. Short-day varieties, which generally don't store well,tend to be mild and sweet. Recommended short-season varieties include yellow onions, such as Texas Supersweet, Yellow Granex, and Texas Early Grano; and red onions, such as Southern Belle, Red Burgundy, Red Grano, California Early Red, and Desert Sunrise. For a short-day onion that's spicy and pungent, and also stores reasonably well, try Red Creole.

Day-neutral varieties are generally very sweet and need about 12 hours of daylight for optimal bulbing. They are often advertised as bulbing anywhere, but they may be more hit-and-miss and slower to bulb than short-season varieties, and may not grow large bulbs in many areas. Few day-neutral open-pollinated varieties are available; try Ailsa Craig Exhibition. Popular hybrid day-neutral varieties include Super Star (white).

Buying/Selection Tips

Onion transplants
Onion transplants
Onion sets
Onion sets

Bulb onions are planted and grown from seeds, transplants, or sets. Transplants are live seedlings, often bare rooted, and often sold in bundles of about 25 plants. Sets are small, dormant onion bulbs grown specifically to give gardeners and farmers a head-start on the growing season, often sold by the pound or in preweighed mesh bags.

Buying and growing bulb onions successfully from transplants and sets can be tricky. GardenZeus recommends growing your own starts or seeding directly outdoors in fall. Short-season varieties that are ideal for many portions of California are not sold as sets. You may find them as transplants (live plants) at local nurseries, online, or by mail order from about September through November each year. Short-season transplants are sold as non-dormant plants. They are actively growing bare-rooted onions, and should be planted promptly; unlike dormant sets, they will not keep for long if unplanted.

Short-day, neutral-day, and intermediate-day onion varieties are generally sweet and mild. Most varieties in these day lengths do not store well and are best for fresh eating. If you want pungent onions that store well, grow the short-season variety Red Creole from seed.

Many local nurseries in the warm inland valleys of California offer bulb onion sets in late winter and early spring. These are often long-day varieties such as Ebenezer White (mild when young, pungent at maturity), Yellow Rock (mild flavor and stores well), and Wethersfield Red or Dark Red Beauty (mildly pungent), which are adapted to growing in the northern United States, and do not bulb well in most portions of California. They will never form the large, full bulbs that you might see on their nursery packaging because of the short day length. Onions grown from sets also tend to bolt early in response to either cold or hot weather.

Soil Needs/Tip

Onions prefer well-drained, loose, fertile soil with a slightly acidic pH in the range of 6.2 to 6.8, and with moderate to high organic matter. You may wish to add compost or well-rotted manure to soils before planting.

Onions are shallow rooted and prefer a moist, friable, loose soil to at least several inches in depth. They grow reasonably well in the clay soils that are common in many portions of California as long as soils are not too compacted, and alkalinity and salinity are not too high. If faced with tough clay soils in your yard or garden, you may do best growing onions in raised beds or containers. In light and sandy soils, onions may need relatively frequent irrigation to bulb well.

Onions are sensitive to salts and sodium in soils, and may develop leaf-tip burn or under produce in soils with high salinity. Bulbs grown in soils high in sulfur will tend to be more pungent in flavor.

Suitable Microclimate

Onions prefer full sun with cool temperatures of 50° to 75° F for optimal growth and bulbing. Onions will tolerate some shade but may produce fewer and smaller leaves, and smaller roots.

Getting Started

Success in growing bulb onions depends on careful selection of variety, proper planting methods, appropriate timing, and careful management of soil moisture. Onions do best in full sun with cool temperatures, and without competition from weeds or other root crops.

Selecting bulb onions varieties to grow in the home garden is more complicated than for most other vegetables. The most important factor for home gardeners is day length, meaning the number of hours of sunlight needed to initiate bulbing and for the plants to form full, mature bulbs. If you have the wrong day-length variety for your time of year and area, onions will form small bulbs or may fail to form bulbs at all. Bulb-onion varieties come in short-day, intermediate-day, long-day, and day-neutral varieties.

To determine your daylight hours, search on the internet for "sunrise sunset calendar" to find sites that will allow you to calculate day length by city. Search sunrise and sunset times for June 21 and December 21, on or near the summer and winter solstices, which are the longest and shortest days of the year, to understand the range of day lengths in your area. The critical day-length time for bulbing is when onion plants have grown large enough to be leaving the seedling stage and beginning to bulb, often about 8 to 10 weeks after germination. GardenZeus recommends deducting an hour per day when calculating day length, to account for twilight times after sunrise and before sunset, with your total day length on a given day (for purposes of growing bulb onions) being the length of time from official sunrise to sunset, less one hour.

- Short-day onion varieties bulb well with 10 to 12 hours of daylight, and are best suited to being grown from fall through early spring in Southern California. Short-day onion varieties are recommended for all areas of California with sufficiently mild winter weather to grow onions outdoors from fall through spring.

- Intermediate-day varieties need 12 to 14 hours of daylight, and are suited for growing from spring through fall in most of California where summers are mild and cool.

- Long-day varieties need 14 to 16 hours of daylight, and may bulb variably to reasonably well from spring to fall in the northernmost areas of California with cool summer temperatures, but otherwise are not suited to growing to mature, full bulbs in California.

- Day-neutral varieties are advertised as bulbing well anywhere, but they do best with 12 to 14 hours of daylight, and may be hit-and-miss from fall to spring in many portions of California.

Other important factors in selecting onion varieties for your garden include storage quality, and taste or pungency. The two main options for taste are American (a strong, spicy-hot flavor) and European (mild or sweet flavored). Both types come in 3 colors of red, yellow, and white.

Watering Tips

Young onion transplants watered with drip irrigation

Onions are shallow-rooted and prefer consistent moisture in the top several inches of soil. Unlike most vegetables, they have difficulty obtaining moisture from below the top 12 inches of soil. The trick with watering onions is to keep the top several inches of soil moist but not wet. Overly wet or poorly drained soils may weaken plants, encourage root diseases, and result in poor bulb formation and low yields.

Onion seeds should also remain consistently moist after they are first watered until sprouts emerge, which may require light watering or misting once or twice per day.

Once established, onions should be watered as infrequently as possible to maintain even soil moisture to a depth of 9 to 12 inches. Generally, if the top 1 to 2 inches of soil is dry, it's time to water onions. Watering frequency for established onions may vary from every 2 or 3 days to every week to 10 days depending upon temperature and soil moisture retention, and with winter rains, onions may go longer periods without irrigation. Generally, onions should be watered more often in light and sandy soils, and less often in heavy or clay soils.

If you like your onions sweet, it's best to err a little on the side of providing extra water; onions that go through periods of water stress or dry soil tend to develop pungency. To maximize bulb size and sweetness, onions need consistent soil moisture from the time sprouts emerge until harvest.

Young onion transplants watered with drip irrigation

Stop watering when the onion tops begin falling over on their own; at this point bulbs have matured and/or are going dormant, won't grow any larger, and should be ready for harvest.

Planting Method/Tips

Bulb onions may be planted as seeds, transplants, or sets.

To plant bulb-onion seeds, space about 2 inches apart or broadcast thinly and cover with ¼ inch of light soil. Keep seeds consistently moist after the first watering, which may require light watering or misting once or twice per day. Onion seeds are often slow to germinate in cool to cold weather; they germinate in about 2 weeks at soil temperatures of 55° F, as compared to a few days at 75° F.

Bulb-onion transplants are live, often barerooted plants (seedlings). To grow your own transplants, start seeds 6 to 10 weeks before transplanting outdoors. Seeds for transplants should be started indoors at temperatures of about 65° F to 80° F .When possible, start seeds in a sunny window; otherwise provide as much light as possible. Onion starts grown in insufficient light tend to be small, slow-growing, and less healthy.

Seedlings that are about ¼ inch in diameter often produce the best and largest bulbs. Larger seedlings are often best planted 2 to 3 inches apart and harvested early as scallions or green onions.

Plant transplants about an inch or two deep in soil, to about ¼ to ½ inch below the spot where individual leaves begin to separate from the main stem, with roots spread and spaced as evenly as possible. GardenZeus recommends minimizing root trimming when transplanting onions, but it may be necessary to trim excessive, tangled, or long roots. As with many transplants, it's best to plant onions slightly lower than the level at which they were grown to protect root crowns and roots, as soil will settle over a few weeks after transplanting. Tamp soil gently after planting.

Growing onions from seeds allows for a much greater diversity in varieties, and seeded plants tend to be more robust, less prone to diseases, and more abundant with yields. It can take up to four or five months for many onion varieties to reach maturity from seeds.

These onion plants are too old to be transplanted
Onion bolting new flower
Onion bolting older flower

Bulb-onion sets are small, dormant onion bulbs grown specifically to give gardeners and farmers a head-start on the growing season. You may wish to purchase onion transplants in sets, but choice of variety in transplants and sets is often very limited. Sets may be planted as soon as they're available from local nurseries or by mail order in late winter or early spring. These are often long-day varieties that are adapted to growing in the northern United States, and do not bulb well in most portions of California. They will never form the large, full bulbs that you might see on their nursery packaging because most of California's short-to-intermediate day length from late winter through fall, and the short spring growing season before hot weather arrives in many portions of the state. They have the additional negative that they have passed through a dormant period and are therefore prone to bolting. They will usually produce small-to-medium bulbs before bolting in spring or summer heat, and are best treated as scallions or green onions for harvest and cooking.

Bulb-onion sets should be planted about an inch or two deep so that the top of the bulb is slightly below the soil surface. Be sure to pay attention to planting the root end down. Occasionally, for a given onion set it may be difficult to determine which is the root end; in this case, plant the set sideways or horizontally a half inch to an inch below the soil surface.

Water onion seeds, transplants, and sets immediately after planting, and maintain even soil moisture thereafter as much as possible for the life of the onions.


Onions at final spacing

Plant onion seeds about ¼ inch deep, spaced about 2 inches apart. Thin closely spaced starts after sprouts emerge, and remaining onion plants to final spacing of 4 to 5 inches after 5 to 10 weeks, when thinnings are large enough to transplant immediately into bare spots in your garden, or to eat as baby scallions.

Space sets or transplants 4 to 5 inches apart, or as close as 2 inches apart if you want to harvest some as scallions or small green onions.


3 to 14 days or longer to seed germination (may take 2 weeks or longer during cool weather of 55° F or below).
Transplant seedlings 6 to 10 weeks after germination.
Early harvest of thinned plants for baby scallions may begin within 5 to 10 weeks of germination.
50 to 90 days to harvest of small-to-medium bulbs
70 to 150 days from germination to harvest of mature roots, depending upon variety and growing conditions.

Pollination Needs/Tips

Because we eat the roots and leaves of onion plants, we prefer slow flowering (slow bolting), and are not concerned with pollination unless saving seeds.

If growing onions to save seeds, they are typically pollinated sufficiently by insects including bees, wind, and gravity.

Interplanting/Companion Planting

Onions provide mild pest discouragement that may help many other vegetables, especially when other vegetables are planted sparsely among denser plantings of onions.

Onions are antagonists to beans and peas; traditionally these plants are believed to stunt or negatively affect each others' growth. GardenZeus expert Darren Butler has seemingly endless bits of gardening lore and anecdotes of unknown origin that knock around and occasionally shake loose inside his head. One such orphaned gardening thought is that some onion exudates, which are substances excreted by plant roots, can be absorbed by pea and bean plants and may result in sour or bitter, oniony-tasting legumes. If this is actually true, with foodie interest in novelty and gourmet vegetables, one might expect onion-flavored peas to headline many a pricey menu, with peas and beans grown inside an onion jungle to have their 15 minutes of fame as the newest trendy cash crop. In any case, traditional consensus suggests that planting onions near peas and beans is unwise to the point of bordering on the perilous.

GardenZeus expert Darren Butler has succeeded well with planting onions and other alliums among strawberries, although pest discouragement for slugs and snails on strawberry fruits is less than some enthusiastic gardening books or websites might suggest (the slugs and snails have all morning or all evening with nothing better to do than find a pathway through your maze of onions to the ripe strawberries that you were just about to pick). Other recommended and traditional companions for onions are lettuce, tomatoes, and herbs such dill, parsley, or mint. Chamomile and summer savory as companion plants purportedly improve the flavor of onions.

Many sources recommend planting onions with other root crops such as beets, carrots, and potatoes, and while these plants may provide benefits to each other, there may also be disturbance to the roots of whatever crops are left in the ground when others are harvested. Carrots are sensitive, especially when young, and harvest of nearby onion roots may cause splitting or forking in carrot roots. GardenZeus recommends caution and extra spacing when planting root crops as companions.

Onions are useful in crop rotation as they repel many of the pests that thrive on other vegetables. If you're having pest problems with any vegetable except another allium, especially with tomatoes, potatoes, and carrots, try rotating onions into the problem area every other year.

Nutrient/Amendment/Fertilization Needs/Tips

Onions need sufficient soil phosphorous and potassium. They are sensitive to salts and easily develop leaf-tip burn in response to fertilization. Bulbs grown in soils high in sulfur will tend to be more pungent in flavor.

Unless your soil is already high in nitrogen, GardenZeus recommends adding nitrogen in the form of diluted urea or a cup of chicken manure diluted in 4 gallons of water (half cup if fresh manure) and mixed thoroughly after seedlings are 2 to 3 inches tall and about once per month thereafter, or twice per month if growing onions primarily for leaves. Adding too much nitrogen may result in lush, high-carbohydrate leaves that attract insect infestation, and may result in leafy onions with small roots.

Onions benefit from moderate-to-high soil organic matter, so when possible prior to planting, work compost or well-rotted manure into the soil. While GardenZeus generally does not recommend using chemical fertilizers, should you choose to chemically fertilize onions, you may wish to use a nitrate fertilizer rather than sulfate because higher soil sulfur content will produce more pungent onions.


Mulching is particularly important for onions to retain even soil moisture and reduce frequency of watering. Use a half-inch of fine mulch for small starts under 4 inches in height; increase to 1 to 2 inches or more of fine to medium mulch after plants are 6 to 10 inches tall. As plants mature, you can mulch as deeply as 3 or more inches.

It's best not to have damp mulch on exposed onions roots and root crowns for extended periods, so if onion roots are exposed, mulch over the soil but generally not the onion roots, and be sure to water more deeply and less frequently, and time irrigation in established onion beds to allow the mulch and the upper inch or two of soil to dry between waterings.

Pruning/Cutting Back/Pinching/Separating

Biennial bulb onions normally do not need pruning, pinching, or separating. If you wish to harvest individual leaves throughout the growing season and still have bulbs at maturity, harvest only a small portion of leaves, no more than 15% to 20% of the plant's total leaf surface, at one time.


From seed. GardenZeus generally recommends open-pollinated, untreated, organically grown seeds.

Bulb onions are commonly grown from sets in your zone, even though the varieties sold locally as sets are generally long-day and won't produce full bulbs in most portions of Southern California.

Container Gardening

Onions are well-suited to container growing, in containers of at least 8 inches in depth, with 12 inches being ideal. All varieties of bulb onions that are otherwise suited to your area can be grown in containers; some may not produce full bulbs, especially if plants are spaced closely or soil depth in containers is constrained, but onions can be harvested at any stage. Bulb onions need spacing of 4 to 5 inches to form mature bulbs. For many varieties, smaller and younger bulbs are sweeter and milder.

Be sure that your containers drain well. Providing the consistent soil moisture that onions require is more difficult in containers and raised beds, especially in light and sandy soil mixes, and you may need to pay careful attention to soil moisture and likely water more frequently than you would for onions planted in the ground.

If growing sets in containers, space closely (about 2 inches apart) and harvest early, often, and at the first sign of bolting, for use as scallions and small-to-medium green onions.

Seasonal Care

Most portions of California are best suited to growing short-day varieties of onion, which are generally grown from fall through spring.

Onions that are seeded or planted in fall may go dormant early in your zone in response to frost or cold winter weather.

Long-day bulb-onion sets generally are not well-adapted to most portions of California. Only in the northernmost portions of California are long-day onions likely to be grown successfully; these onions can flourish and grow in the 'long" days of the northern summer.

How to Harvest

Both of these onions are ready for harvest; some onions push up out of the ground more than others

Leaves and roots of bulb onions can be harvested at any time after they reach a desired or reasonable size for eating, from baby scallions to mature bulbs. If harvesting before maturity, you may need to brush soil away from around onion roots or probe gently with your fingers to determine root size before harvesting.

If you wish to harvest individual onion leaves throughout the growing season and still have bulbs at maturity, harvest only a small portion of leaves, no more than 15% to 20% of the plant’s total leaf surface, at one time.

Because they tend to have shallow roots, onions can often be pulled directly from the ground by grasping at the base of the leaves and pulling firmly. It may be necessary to push a spading fork, trowel, or shovel into soil about 2 to 6 inches inches from the onion root(s) and gently loosen the soil before harvesting.

Traditionally, mature bulb-onion crops are often harvested in their entirety about 7 to 14 days after the tops begin falling, or after about half to 2/3 of the tops are down.

While most short-day onions that are suitable for many portions of California do not store well, the occasional pungent variety, such as Red Creole, will store for several weeks to several months. To harvest bulb onions for storage, allow them to grow to full maturity. When half to 2/3 of onion tops have yellowed and fallen, harvest the entire crop with tops still attached. Rinse and clean the bulbs with plain water to remove soil and allow them to dry outdoors for 2 to 3 weeks, arranged with space between bulbs for air circulation. The first few days of drying are best in sunlight during cool weather, or in shade during warm-to-hot weather, and thereafter bulbs should be dried in natural light with shade, and out of the rain.

Harvesting Tips

It's best to stop watering bulb onions when 10-25% of the tops have fallen. If you discontinue watering too early, you may decrease your yield slightly, but continuing to water bulb onions as they go dormant can result in disease, split roots, and other problems.

Onions that are harvested when immature generally do not store well and are best for fresh eating.

Onions that begin to bolt at any time during the growing season should be harvested and eaten immediately. They will become bitter or unpalatable as the plant goes to seed, and will not store well.

What Commonly Goes Wrong

Unsuitable Varieties for Day Length: Choose appropriate onion varieties for the day length of your season and area. Inappropriate varieties for day length may produce small or no bulbs, and may bolt or go dormant early or unseasonably. See GardenZeus sections "Recommended Varieties/Cultivars" and "Getting Started" for more information.

Unseasonable Planting: Onions are cool-season crops. Onions seeded or transplanted at teh wrong time will not yield well.

Overly Pungent or Bitter Bulbs: Onions tend to become more pungent the longer they are in the ground, and some varieties that are mild when young or even at maturity may develop pungency if left unharvested. Bulb onions that have been water-stressed or had periods of soil dryness may also become more pungent, and onions lose sweetness and flavor quality, or may become bitter, after bolting.

Small , double, and split bulbs are usually caused by water stress, uneven watering, or periods of soil dryness between watering. Split bulbs can also be caused by overwatering while onions are going dormant or during dormancy. Small and misshapen roots have many other potential causes, including wrong variety for day length; obstructed, compacted, or uneven soil; overcrowding; overly wet or waterlogged soils; overly alkaline or acidic soils; root disturbance or shock; and nematodes.

Slow growth, lack of vigor, small plants, production of few or small roots or leaves, dried out or folded leaves, yellowing leaves on immature plants: These common symptoms may result from soil pH that is too high or too low, compacted soil, alkaline soil, overwatering, underwatering, irregular watering, poor drainage, cold or hot weather, lack of soil nitrogen, other soil nutrient deficiencies, planting rootbound or senescent transplants, or a combination of these. May also be the result of wind or other environmental and abiotic factors.

Brown and dead leaf tips or edges: Burned leaf tips often result from over fertilizing, sodic soils, animal urine, over application of manure or urea, or soluble salts in soils.

Bolting: Onions may begin to flower and go to seed if they are exposed to a cold period or frost followed by a warmer period, if left in the ground too long, as a result of water stress or repeated wilting, in general in response to hot or cold weather, or naturally as a result of their biennial reproductive cycle. There is nothing that can be done to reverse or stop bolting once it begins. Bolted onions will rapidly degrade in quality for eating, and won't store well. Harvest and eat roots immediately after plants bolt, unless saving seeds.

Not a Problem

As bulb-onion roots swell and mature, they often literally begin to push themselves out of the soil, sometimes to the point that most of the onion root is above soil. This particularly happens in tough or compacted clay soils, and seems to be more common and pronounced when growing onions from sets. It's not generally a problem to have a significant portion of an onion root exposed above soil and generally, when onions are grown during cool weather and when their cultivation needs are otherwise met, GardenZeus expert Darren Butler has not seen root quality affected negatively when onion roots are exposed above soil level. Breathe out, do your happy thing or stress-release pose, and let it go. Onions are naturally shallow-rooted, so if your bulbs are pushing out of the soil, you may need to water more frequently to keep the top few inches of soil moist. Otherwise, no tears, except when taking a large first bite of an unexpectedly pungent raw onion bulb!

Yellowing leaves are sign of a problem in onions, right? They can be (see "What Commonly Goes Wrong," above), but then again, maybe not. (Darren--I really like this section, but I am not sure how to modify it for general audience without zone information.) Onion leaves yellow and brown naturally when the roots mature, or whenever the plants decide that it's time go dormant, which may happen at unexpected times in your zone, particularly in response to cold snaps in fall or winter. Your zone can be tricky for growing mature onion bulbs; they need to be grown in cool weather, which is only available to you from fall through early spring, but onion biology sometimes rushes to judgment and may interpret shortening fall days and overnight winter frosts in your zone to mean that much colder and more severe weather is soon to come. In onionspeak (a language with which GardenZeus expert Darren Butler is reasonably conversant but still sometimes misses nuances, especially the subtle phytochemical signals for which he lacks the proper biochemicals to interpret) this translates roughly to: "Alert! We seem to have been planted in North Dakota just before winter and we are about to be covered in snow! Something must be done immediately!" and understandably, they may then decide to go dormant, thus producing yellowing and browning leaves, even if bulbs are still small. There's not much for a Southern California gardener to do in such cases except click the tongue or say "tsk-tsk" a few times at the fussiness of onion biology, celebrate the general lack of snowstorms which may be a major part of your preference for living in Southern California, appreciate our sunny winter days, respect North Dakota from a distance, harvest and enjoy eating your onions at whatever size they reached before cold weather panicked them, and replant a different variety as soon as possible. If onions go dormant late in winter, try sets in spring; or, plan to try again with a different variety of short-day seeds and transplants next fall.

Common Diseases

Diseases on onions can be minimized by growing during cool weather in reasonably fertile, well-drained soil with a living soil ecosystem, watering at the soil surface or with drip irrigation rather than from overhead or with sprinklers, and maintaining even soil moisture without allowing soils to become wet or waterlogged.

Damping Off: Caused by soilborne fungi that may suddenly kill smaller seedlings and starts. Occurs most commonly in cool, damp soils.

Rotting roots: Usually the result of disease organisms that thrive in wet and anaerobic soils, or bacterial rots that start on leaves and spread to roots, and which are encouraged by overhead or sprinkler irrigation, but can occur in a range of soil and growing conditions. Provide better drainage and/or reduce watering. Rotate crops and avoid planting onions repeatedly in the same soil, or in soil where other alliums were grown recently. Encourage a healthy, living soil ecosystem that will help keep soil diseases in check.

Mildews: Powdery and downy mildew appear as a whitish circles or whitish-to-purple layers on the upper or lower surfaces of leaves, yellowing or dead spots, or pale-green or yellow leaf sections, and may be mistaken for other problems, such as nutrient deficiencies. Powdery mildew is more commonly a problem in your zone than downy mildew. Avoid wetting foliage when watering. Some mildews can be discouraged using a nontoxic homemade spray of one tablespoon each of baking soda and tea tree oil per quart of water, shaken vigorously and regularly as applied via spray bottle. Mildews are often difficult to control and are best managed through prevention and good cultural practices, such as planting resistant varieties, planting in areas with good air circulation, keeping foliage dry, less-frequent irrigation at soil level rather than overhead or from sprinklers, encouraging biologically active "living" soil that will support strong plant immune systems, and rotating crops. Mildews are often not fatal and onions may produce reasonable yields of roots and fresh uninfected leaves despite ongoing infections on older leaves. Mild infections of mildew on onion leaves do not normally affect root quality, but severe infections, especially during warm-to-hot weather or over long periods, can cause root quality to decline.

Common Pests

Onions grown in home gardens tend to have fewer issues with insect pests as compared to most vegetables, and are often touted as discouraging pests, although in practice, GardenZeus expert Darren Butler has generally found the pest-discouragement powers of onions to be more limited than many reference sources claim.

Onions also tend to have fewer issues with vertebrate and mammalian pests, and generally are passed over by rabbits, deer, gophers, and rats, although Darren has long believed that one very-specific question is generally missing from pest-management thinking and planning: How hungry are the pests? If your pest mammals have plenty of other forage, your onions will likely remain untouched. If it has been a dry year or there's not much else for wild animals to eat, your onions may disappear overnight as though they were the sweetest ripe corn or most-tender spring greens.

Insect pests cause more problems with commercial onion farming than in home gardens. Here are a few pests that you may see occasionally in your zone:

Onion thrips are the most common insect pest of onions in many portions of California. They are very small, thin, light-brown, winged insects that are difficult to see with the naked eye. They feed on leaves, and often are not a problem for bulb harvest in home gardens, but may become so at high populations. Onion thrips are most common in dry, warm-to-hot weather, such as when attempting to grow onions in weather warmer than is ideal for your variety of onions. They are difficult to control organically in home gardens; the best response may be to encourage beneficial insects that are natural predators, such as predaceous mites and lacewings.

Onion maggots attack germinating seedlings or feed on both young roots and maturing bulbs. Leaf tips turn brown and plants turn yellow, wilt, and die. If you develop problems with onion maggots, rotate crops and avoid planting in soils high in undecomposed organic matter, particularly fresh manures.

Stem and bulb nematodes are microscopic worms that live inside plant tissues and feed on onion stems, leaves, and bulbs. It is difficult to diagnose a nemotode problem from symptoms alone, as nematode symptoms have multiple other possible causes; a lab test is generally required to confirm nematode infestation and identify species. Seedlings may become pale, stunted, spotted, thickened, and/or deformed. Mature plants may become limp or soft, and may be more prone to secondary infections from bacteria and fungi. Nematode infestations are difficult to control. Avoid planting onions or other alliums again in infested soil. For severe infestations, it may be necessary to fallow soil or grow non-host crops for your specific nematode species for two to several years.

Special Care

Don't share onions or food containing onions with your furry pets. Onions contain thiosulphate, which is toxic to cats and dogs, and relatively small amounts can cause a fatal reaction in your pets.

Special Info

Onion tears are caused by a gas that combines with water in your eyes to produce an acid. GardenZeus expert Darren Butler's preferred solution to onion tears is to wear airtight goggles, which may also serve pleasingly to contribute to one's reputation as a nonconformist and freethinking gardener and cook, particularly with friends of teen-aged children or colleagues of one's spouse when they happen upon you happily cooking in the kitchen while wearing goggles. If this invites humorous comments about the toxicity of your culinary attempts, protection being needed from you cooking, or perhaps about your status as an aeronautical or aquatic chef, feel free to invite the joker to slice the onions for you without the goggles.

Other solutions to onion tears include dicing or chopping onions with a small fan to one side blowing across the cutting board, slicing onions underwater (this does not work so well if chopping or dicing), or sticking your tongue out and breathing through your mouth, which draws at least some portion of the offending onion gas onto your tongue and away from your eyes.

To clear out onion breath, eat a sprig of parsley, rinse your mouth with lemon juice and water, or chew on a citrus peel. Many other acidic or bitter foods, from mustard to various aromatic herbs, will also negate or mask onion breath.

Sustainable Landscaping Tip

Biennial bulb onions are not good candidates for naturalizing because they need more consistent moisture than is provided by natural winter rainfall in your zone. They will produce good yields with little management or maintenance in fertile, sunny areas that remain naturally moist throughout the cool season in your zone. For growing onions in sustainable and permaculture gardens, GardenZeus expert Darren Butler recommends perennial potato onions.

Advanced Tip

If you want to grow intermediate-day onion varieties in your area, consider extending the growing season by starting seeds indoors at temperatures of about 65° F to 80° F for later transplant outdoors. When possible, start seeds in a sunny window and otherwise provide as much light as possible.

You may be a fan of growing, cooking, or eating onions, but have you considered their mystical, spiritual, and symbolic aspects? In ancient Egypt the onion was revered as an object of worship; with its concentric rings and spherical shape, it symbolized eternity and was used in the mummification of pharaohs. There is a small religious sect in France, founded in 1929, known as Les Adorateurs de l’Oignon, the Worshippers of the Onion. Their insights include recognizing the onion as a symbol of the conservation of energy, and an observance and appreciation of the power of onions to renew themselves and produce newer, better bodies for themselves year over year. Many other modern, ancient, and indigenous cultures and traditions, including Egyptians, Hindus, Greeks, Wiccans, Peruvian shamanic traditions, other indigenous and shamanic traditions, and others have found alliums and/or onions to be powerful medicinally, as an aphrodisiac, and/or mystically and spiritually. Not everyone agrees that onions should be eaten regularly, including Jainist vegetarians and many Ayurvedic cooks and adherents, who eschew onions and garlic because as rajasic and tamasic foods for spiritual and health reasons, including that they are traditionally seen as promoting passion, laziness, and ignorance.

Preservation, Storage, and Use

Storage onions grown to full maturity may last several months when stored under ideal conditions of 32° F and high humidity. Bulb onions harvested before maturity and mild, short-day and intermediate-day varieties may have a shelf life of only days to weeks, or may last weeks to months if stored properly. Commercial onion storage is at 32° F with 60% to 70% humidity. To extend storage life of roots, remove tops and cull out all diseased or injured roots that might spread infection to others. Wash all soil from roots and allow to dry thoroughly.

Humidity in refrigerators is too low for long-term onion storage; roots may last weeks to a month or two, but eventually will dry up, soften, and shrivel, especially small or immature roots whose surface area is disproportionately greater as compared with larger onions. If storing bulb onions in your refrigerator, do so in a humid produce drawer with humidity turned to high (ideally 60% to 70% humidity at temperatures close to freezing), or with an open bowl of water, and/or in cloth or paper bags to reduce drying.

If storing at warmer temperatures, such as without refrigeration, keep onions completely dry and store with space between bulbs, such as on trays or in hung bunches, in a cool, dark area with low humidity and good air circulation. Don’t store onions near potatoes or fruits as these may release a ripening gas that will reduce shelf life for onions.

Storage length for onions is directly related to their pungency; the same substances in onions that make them pungent in flavor also inhibit bacteria and fungi that cause them to go bad. Sweet and mild onions generally do not store well.

Onions are not sensitive to the ethylene gas produced by most fruits.

Onions are a basic ingredient in a variety of cooking traditions. And they are versatile; they can be eaten raw or cooked. Mild, short-day or intermediate-day onions are generally preferred for fresh eating, while pungent and strong-flavored onions are often used for cooking. Mild, short day or intermediate-day onions are best eaten raw: slice them for sandwiches or chop them for salads and salsas. Try slicing mild onions and using them in a grilled cheese sandwich. When properly cooked, long day onions develop into exquisite concoctions. These onions can be sauteed, boiled or roasted and are used to flavor sauces, soups, stews, stuffing and juices.They can be fried as onion rings, and they can be grilled or pickled. They are an essential ingredient in the french mirepoix, a combination of onions, celery and carrots that forms the basis for many sauces, stocks and soups. For a particularly memorable dish, caramelize onions by slicing them into 1/8 inch thin rings, then adding olive oil and unsalted butter. Cook on medium until onions have softened, then reduce the heat to low and cover the pan, cooking for 45 to 60 minutes. Taste, and add a small amount of brown sugar if desired. Use the caramelized onions with beef or on pizzas. Onions are low in calories and retain their nutrients well when cooked.

Onions have proven and presumed health benefits, including supporting healthy blood, bones, and digestion, among many others. Research has proven that eating onions frequently can help to increase bone density; onions may be helpful to those with thin or weak bones, including those suffering from osteoporosis and menopausal women. Onions also may support healthy connective tissue, and are a good source of the antioxidant flavonoid quercetin, which may provide anti-inflammatory benefits throughout the body, and may reduce pain, swelling, and stiffness in joints.

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