Onions are easy to grow and can be planted from seed, transplants, or small bulbs called sets.
As they mature, onion plants form bulbs in response to changing temperatures and day length.
They are planted in the fall or spring, depending on location.
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Light
Onions need full sun for highest yields, at least 6 hours a day.
Soil
They require consistently moist, well-drained soil with a pH between 6.0 and 7.0.
Loamy soils high in organic matter are best though onions tolerate sandy and clay soils.
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Sandy soils require more fertilization and irrigation to maintain even moisture.
Clay soils commonly produce hotter onions.
Both can be amended with well composted organic matter to improve tilth.
Water
Onion plants have a shallow root system and require even moisture for growth and development.
Plants require one inch of rainfall or irrigation per week, ideally delivered through drip irrigation or furrowing.
Young, establishing plants and those planted in sandy soils require watering more than once per week.
Though plants tolerate cold, seedlings will grow slowly if soil and air temperatures are too cold.
Avoid setting plants out too early.
Prior to planting, work a balanced (10-10-10) fertilizer into the soil along the intended planting line.
Types of Onions
Bulb initiation in onions is triggered by changes in day length.
It is critical to select an onion variety that matches your region.
Short Day Onions
Short day onions begin producing bulbs when daylengths reach 10-12 hours.
In northern regions, they bulb too early to produce a good-sized bulb.
Short day onions typically have a mild, sweet flavor, and are best eaten fresh.
They perform well through much of the United States, except for the far south.
Intermediate day onion varieties tend to be very sweet.
This group has excellent storage qualities, and many have a strong, pungent flavor.
Shallots and potato onions belong to the Aggregatum group, (Allium cepavar.
aggregatum) and produce clumps of smaller bulbs rather than one large bulb.
Most shallot varieties are considered long day.
Chives, walking onions, leeks, and Welsh onions belong to different species ofAllium.
Planting time varies depending on the pop in of start you are using as well as your local climate.
In northern gardens, onions are started in the spring for a late summer or fall harvest.
Southern gardeners can start onions either in fall or late winter for an early summer harvest.
Growing Onions from Seed
The most economical method for growing onions is from seed.
Seed also provides the greatest availability in terms of variety selection.
However, growing onions from seed is also the most difficult, with uneven germination common.
In southern gardens, direct sow seed in fall or late winter.
Growing from sets is very easy, but plants may be susceptible to bolting.
Sets are widely available at garden and agriculture centers or can be ordered from seed catalogues.
They are more expensive than seed and the variety selection is extremely limited.
Purchase sets that are no more than an inch in diameter.
Growing Onions from Transplants
Onion transplants are seedling onions ordered from seed companies.
They come in small bundles of dormant plants, each the thickness of a pencil.
Onion transplants produce more reliably than sets and are less prone to bolting.
They also tend to be available in a wider variety of cultivars.
Harvest the onions when one half to three quarters of the tops have fallen over.
Use a spading fork to dig beneath the onions and lift them from the soil.
Harvested onions need to cure before storage.
The neck of the bulb will also tighten.
Once cured, you could trim the tops off.
Store onions in a cool, dry place.
Do not allow bulbs to freeze.
In the home garden setting, diseases are seldom a problem.
However, good cultural practices can help prevent plant diseases.
Plant onions in different parts of the garden each year, a practice called crop rotation.
Planting in a well-drained soil or on raised beds is also beneficial.
Thrips and onion maggots are the two most common insect pests.
Thrips overwinter in weedy areas and on onion bulbs not removed from the garden.
Good sanitationkeeping the planting area free of debriscan help manage this pest.
Onion maggots feed on the roots and bulb, which can lead to bulbs rotting during storage.
Crop rotation will help with maggots, as will good sanitation.
Onion maggots are attracted to undecomposed organic matter such as manure and rotting foliage.
Do not amend soils with fresh manures, use only well composted organic matter.
Common Problems
The most common problem with onion production is bolting, or premature flowering.
If this happens, harvest the onions and use them like green onions or scallions.
Onions bolt for a variety of reasons, mostly driven by temperature fluctuations.
A period of good growing weather followed by a prolonged cold snap can trick the plants into flowering.
Likewise, a cool spring followed by high heat can induce bolting.
Bolting can be limited by planting at the right time for your area.
If using onion transplants, check that they are no larger than a pencil.
Onion sets should be an inch or less in diameter.
Onions are a rewarding crop to grow.
They take up little space and fit almost anywhere in the garden.
you could even tuck them into your flower beds.
When selecting varieties to grow, consult growers at your local farmers market.
They will know the best varieties for your region.
Colorado State University.Guide to poisonous plants.
