How to Plant, Care for, and Harvest Onions

Onions are in nearly every garden and kitchen in the world for their pungency and versatility for many culinary purposes. Growing onions at home has its advantages and is relatively easy to grow. One good thing about onions is that they could be grown by mualtiple planting options, such as seeds, sets, or transplants, and they grow quite well in almost all types of climates. Onions are an extremely prolific vegetable by nature, and if cared for properly, can be stored for a few months. Because of this, they lend themselves very well to being part of any gardener's rotation. 

Common Name	Onion
Botanical Name	Allium cepa
Family	Amaryllidaceae
Plant Type	Biennial (grown as an annual)
Size	Bulb diameter: 2-4 inches; Foliage height: 12-18 inches
Sun Exposure	Full sun (6–8 hours of sunlight)
Soil Type	Loose, well-drained, and fertile soil
Soil pH	Slightly acidic to neutral (6.0–7.0)
Temperature	55–75°F (ideal for bulb formation)
Hardiness Zones	3–9 (depends on variety)
Companion Plants	Carrots, lettuce, beets
Native Area	Central Asia; cultivated worldwide

Best Varieties of Onions

The first thing to remember when choosing onions is that they are daylight-sensitive. The main categories are

• Long-day onions: These can be grown in northern regions that have the longest summer days, hence can receive more than 14 hours of sunlight. Varieties include 'Walla Walla', 'Yellow Sweet Spanish', which have mild, sweet flavors but unsuitable in hot regions.

• Short-day onions: These are ideal for southern regions, plants needing from about 10 to 12 hours of light. They can be set in the fall for an early harvest. Popular varieties include 'Texas Sweet' and 'Red Creole'.

• Intermediate-day onions: Falling into the more northern and southern climates with day length averaging 12-14 hours of sun per day are varieties such as 'Candy'.

Choosing an onion variety that is compatible with your area's growing conditions will go a long way toward getting the best possible bulb development. Some onions are suited more for fresh use and others for long storage.

Preparing the Soil for Planting

Onions will thrive best in loose, well-draining soil with good fertility. Plants of onions prefer sandy loam because it has shallow roots that can spread out easily. Compost or aged manure added before planting will help improve the soil structure while adding nutrients for development. Optimum nutrient availability occurs within a pH range of 6.0-7.0. If your soil is heavy or prone to compaction, raised beds are one surefire way to avoid waterlogging, which, in particular, onions abhor.

How to Plant Onions: Seeds, Sets, or Transplants

There are three major ways of rearing onions, all with their own advantages.

• Seeds are inexpensive, but they must be started indoors extremely early-8 to 10 weeks before the last frost. They are then planted outdoors when they are about 6 inches high.

• Sets  are the easiest for a beginner since they start fast and more surely when set directly in the garden.

• Transplants give a head start to the growing season and earlier harvests because they have already been nurserygrown as seedlings.

Space plants 4-6 inches apart so that bulbs can develop to full size, but set rows 12-18 inches apart. Onions planted too close together in proximity compete with each other for nutrients, resulting in smaller bulbs.

Watering and Feeding Onions

As the onions have fairly shallow roots, they get dried up in case of hot weather. Continuous watering with regular application of fertilizer provides them with a healthy birth.

• How Much to Water: Onions need approximately 1 inch of water in a week. If there is a scarcity of rainfall, irrigation should be used to supplement the crop. That would retain the bulbs from splitting. Drip irrigation can help in this respect because it retains the soil moist without wetting the leaves.

• Fertilization: During the early phase of growth, onions require nitrogenous fertilizer. As soon as the bulbs begin swelling, cut down on the nitrogen and replace with phosphorous-based fertilizers for the growth of the bulb.

Keep a balance since over-fertilization will retard the formation of bulbs and give you foliage galore.

Growing nions in Containers

Onions thrive well in containers and are ideal for small-space gardeners. Just remember the pot should at least be 12 inches deep to leave a suitable area for the root system. Use very good-quality potting soil with compost for freshness. Containers dry out a lot quicker than garden beds, so keep your eyes on the soil moisture, watering when the top inch has dried out. Keep them regularly fed with diluted liquid fertilizer for a healthy crop throughout.

In addition, it even allows one growing onions in pots to change their position to capture most of the sunlight, something that is quite important for good growth, especially in small areas.

Weeds and Pests Control

Weeds compete with the plants for water and nutrients while the pests could give significant damage if not properly taken care of.

• Weed Control: Mulching around the base of the plant prevents weeds from taking over. Organic material mulch, such as straw or shredded leaves, helps to retain moisture. The most effective way to remove weeds would be by hand-pulling; this would not bother shallow roots.

• Pest Management: Common pests include onion maggots and thrips. One can prevent the maggot infestation by using row covers, whereas one can use a neem oil spray on thrips.

By frequent scouting of onions, a grower should be in a position to find the various problems at any one time in the season before an advanced stage sets in.

Diseases of Onion Plants

Growing onions can also be very problematic considering the many plant diseases that may affect the health of an onion and possibly its yield. Accurate awareness along with early disease detection is of essence to maintaining healthy onion crops.

1. Downy Mildew

This can easily be identified by the yellow discoloration on leaves that have purplish-gray fungal growth on their underside. It has often been observed during cool and humid weather. This disease is actually caused by a fungus known as Peronospora destructor.

• For control and prevention of downy mildew, allow good aeration around plants through good spacing. Avoid overhead watering in order to decrease humidity around the foliage. Do crop rotation annually.

2. Neck Rot

Neck rot Neck rot appears as soft, watery decay of the neck of the bulb during storage and is often associated with an offensive odor. The causal agent of the disease is the fungus Botrytis allii. It is promoted by pulling onions when the weather is wet.  

• Control of neck rot Cure pulled onions in a warm, dry place for some days before storing. Store onions in a cool, dark place with adequate ventilation to minimize possibility of rot.

3. Fusarium Basal Rot

Symptoms include yellowing and wilting of the foliage, with brown rot on the base of the bulb. The disease is caused by Fusarium fungi that are favored by wet conditions and can survive in the soil for several years. 

• Prevention involves disease-free seeds or sets and crop rotation. Improvement in soil drainage helps to avoid waterlogged conditions.

4. Purple Blotch

Look for small, water-soaked lesions that center upon the leaves. They develop into purple-brown spots with yellow edges. The disease is caused especially by the fungus Alternaria porri under conditions of high humidity.  

 

• To prevent the disease purple blotch, make sure there is good drainage and air circulation around the plants. Remove all infected plant debris from the garden, and prevent overcrowding, as this will reduce the spread of the disease.

 

5. White Rot

Symptoms include yellowing of the leaves alongside a cottony white growth of fungus at the bulb base usually containing several small black sclerotia. This is caused by Sclerotium cepivorum, which can remain in the soil for several years. 

• Some of the prevention methods effective in this case include long crop rotation cycle, about 4–6 years along with soil sterilization techniques in the infested areas.

6. Onion Smut

This disease manifests as small dark blisters on leaves that later break open, resulting in stunted growth and a yield reduction. Onion smut is caused by the soil-borne fungus Urocystis cepulae.  

• In managing this disease, employ the use of resistant onion varieties and avoid planting on infested soils, besides observing good sanitation and crop rotation.

7. Bacterial Soft Rot

Soft rots of bulbs, caused by bacterial pathogens, result in soft, watery tissue that often develops a disagreeable odor as tissue breakdown ensues. The following bacteria enter the plant through injuries under wet conditions.

• To reduce the possibility of infection by bacteria, handle onions carefully during harvest to prevent abrasions and avoid overwatering. Proper storage conditions will also aid in reducing proliferation of bacteria.

Knowing these diseases and taking the right prevention measures will safeguard the onion crops for the gardener and help them in getting a good yield. Again, as has been said, regular monitoring is a must, especially maintaining good hygiene in the garden in order to control diseases in onions effectively.

Prevention of Bolting

Bolting sets in when the onion plant produces a flower stalk prematurely. This is usually brought about by temperature; hence, it saps all the energy away from developing a decent bulb, trimming down yield and quality. Plant at the correct time for your region to avoid bolting. Keep the water level consistent. If you're lucky enough to catch a flower stalk, pull it off immediately. This will make the plant's energy be diverted into the bulb that is forming.

How to Harvest Onions 

Onions are ready to harvest when the tops start to yellow and fall over on their own, which is generally in mid-to-late summer. You can pick green onions earlier in the season when they are young and tender. To do this, you will need a garden fork to carefully lift the bulbs from the soil, being careful not to bruise the bulbs in the process.

Allow pulled onions to dry in the sun several hours before taking them inside to complete the curing process. This initial drying step hardens the outer layers and prepares the bulbs for longer storage.

Curing and Storing Onions

Proper curing of onions extends their storage life. Spread them out in single layers in a well-ventilated, shaded area for two to three weeks. After the outer skins are dry and papery, trim off the roots and cut the tops back to about an inch.

Store cured onions in mesh bags or wood crates in a cool, dark location with good ventilation. Optimum storage temperatures are from 35°F to 50°F with low humidity. Do not store onions in close proximity to potatoes because potatoes off-gas moisture in the form of water vapor and this may encourage spoilage of onions.

FAQs

How long does it take to grow onions?

Onions grown from seed take about 90 to 120 days to mature, and sets are then thinner and partly grown, taking about 60-80 days to mature. Planting onions from seeds allows one to have options in terms of a broad range of varieties with interesting flavors. Sets are easy to handle and speed up one's harvest. Soil and temperature conditions might also affect the growth time of onions.

Does an onion prefer partial shade to grow?

While onions thrive under direct sunlight of 6–8 hours daily, they do stand light shade. Prolonged shade, though, does tend to produce slow growth with relatively smaller bulbs. When planting under partial shade, keep your soil well drained and add in extra nutrients to try to help along the growth of your onions.

How often should I water onions?

Water onions once a week with about 1 inch of water, taking care to have the soil equally moist but not waterlogged. As a matter of fact, consistent moisture during the time when they start bulbing is really important, for this would make quite a difference between splitting or stunted bulbs. Avoid overwatering with care, for it invites fungal diseases in onions, including onion rot.

Why aren't my onions forming bulbs?

Poor day length is probably the most common reason onions fail to bulb. Long-day onions need 14 to 16 hours of daylight, while the short ones need 10 to 12 hours. Other causes for poor bulb formation are over-crowding the plants, nutritional deficiencies or excesses, and poor choice of variety for the climate. Adjust spacing, fertilizer application, and selection of variety to overcome this problem.