How to Grow Onions: The Complete Guide (2024)

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Select a location with full sun, where other plants won’t shade your onions. The more energy they can get from the sunlight, the larger their bulbs can grow. Mix aged manure or compost into the soil in the fall or early spring to improve texture. Ensure there are no rocks or debris. Soil needs to be well-draining and loose; compacted soil affects bulbdevelopment.

When to PlantOnions

• In spring, plant onion sets outdoorsas soon as the ground can be worked, usually in late March or April, when temperatures are no longer likely to dip below 28°F(-2°C).
• In spring, startonion seeds indoors for about 6 weeks before transplanting to the ground (once the soil is at least50°F).
• A fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. They will remain dormant during the cool season; as the temperatures and soil warm again in early spring, the onions come back tolife.

How to PlantOnions

Onion plants are heavy feeders and require constant nourishment to produce big bulbs.At planting time, add nitrogen fertilizer. Many organic gardeners will add an inch of compost to the bottom of each row before planting.Or,dig a trench in the soil about 2 inches deep and 3 inches wide, and then fill the trench back in with about an inch ofcompost.

• Bury onion sets 2 to 6 inches apart, gently pressing them 1 to 2 inchesdeep into loose soil. (Use the closer spacing if you want to pull immature onions asscallions.)
• Space transplants 4 to 5 inches apart androws 12 to 18 inchesapart.
• Set the bulbs with the point end up. Again, don’t bury them more than 2inches under the soil. It’s critical that onions aren’t planted too deep, as this can affect bulbdevelopment.
• Mulch with straw between rows to help retain moisture and stifleweeds.

We find it helpful to think of onions as a leaf crop (like lettuce or kale) rather than a root crop (like beets or carrots). Fostering healthy foliage growth ensures the plants have enough energy to form largebulbs.

• Ensure immature bulbs stay covered with light mulch to protect them, retain moisture, suppress weeds, and allow aircirculation.
• Do not cover emergingonions.
• Fertilize every few weeks with nitrogen to get big bulbs. Stop fertilizing when the onions push the soil away, and the bulbing process has started. Do not put the soil back around the onions; the bulb needs to emerge above thesoil.
• Generally, onion plantsdo not need consistent watering if light mulch is used.About 1 inch of water per square foot per week, including rainwater, is sufficient. If you want sweeter onions, water more. To deter bolting, water often during hot spells.
• To deter thrips, intercrop onions with tomatoes or carrots in closely alternatingrows.

See our video demo to see how to plant and grow perfectonions!

Onions are photoperiodic (sensitive to daylight), so different varieties have been bred for varying day lengths. The border between long- and short-day varieties lies roughly at 36 degrees north latitude (the 36th parallel). North of that, plant long-day types; south of it, plant short-day onions. Or, try “day-neutral” (intermediate) varieties, which yield an excellent crop anywhere, regardless of daylength.

Long-dayvarieties:

• ‘Yellow Sweet Spanish’: large, roundshape;yellow-white.
• ‘First Edition’: high-yielding, stores well, flavorful,creamy-yellow
• ‘Red Wethersfield’: flat bulbs that store well, white flesh,red-skinned
• ‘Aisa Craig,’ ‘Walla Walla’: hugebulbs
• ‘Buffalo,’ ‘Norstar’: produce early but keep only until lateDecember
• ‘Copra,’ ‘Southport Red Globe,’ ‘Sweet Sandwich,’ ‘Yellow Globe’: keepwell
• ‘Red Florence’: oblongshape

Short-dayvarieties:

• ‘Stuttgarter’: sold in sets, early maturity with slightly flat shape,yellow
• ‘White Bermuda’: extremely mild, with thick, flat bulbs;white
• ‘Red Burgundy’: good table onion with mild, sweet white inside; short-termkeeper
• ‘Crystal Wax White Bermuda’: a great onion for pickling when harvested at “pearl”size
• ‘Hybrid Yellow Granex’: sweet, Vidaliatype
• ‘Southern Belle’: ruby-colorthroughout
• ‘Texas 1015-Y Supersweet’: storeswell

Day-neutral, or intermediate,varieties:

• ‘Candy’: golden,thick-flesh,jumbo bulbs; storeswell
• ‘Red Stockton’: large, red-ringed, white-fleshbulbs
• ‘Super Star’: large, sweet, whitebulbs

Pull any onions that send up flower stalks. This means that the bulbs have stopped growing. These onions will not store well but can be used in recipes within afewdays.

• Spring-planted onions tend to be ready for harvesting bymid-summer.
• When onions start to mature, the tops (foliage) become yellow and begin to fall over. At that point, bend the tops down or even stomp on the foliage to speed up the final ripeningprocess.
• Loosen the soil around the bulbs to encouragedrying.
• Harvest by late summer in dry weather. (Wet-harvested onions do not cure well and might rot instorage.)
• When the tops are brown, pull the onions. Handle them carefully, as the slightest bruise (now and in storage) willencouragerot.
• Cut the roots and trim the tops back to 1 or 2 inches (but leave the tops on if you are planning to braid the onionstogether).

How to StoreOnions

• Set onions on dry ground for a few days to cure, weather permitting, or in a protected place such as a garage orbarn.
• Once cured, hang onions in a mesh bag or nylon stocking; spread up to two layers deep in a box; or braid and hang them in a cool, dry, well-ventilated area. The ideal temperature range for storage is 40 to 60°F (4 to 15°C). Do not store in a refrigerator, as conditions will be toodamp.
• Check periodically for sprouting or rotting onions and removethem.
• Don’t store onions with applesor pears, as the ethylene gas produced by the fruits will interrupt the onions’ dormancy. Onions may also spoil the flavor of thesefruits (as wellaspotatoes).
• A pungent onion will store longer than a sweet onion. Sweet onions have a high water content and do not keep well. Eat the sweet varieties first and save the more pungent onions forlater.

Check out this video to learn how to harvest and storeonions.

Catherine Boeckmann