Whether you garden in the ground, in raised beds, on the windowsill, or anywhere else, onions are a great addition or re-addition to your plant family. Read on for simple, straightforward specifics about growing onions.
This onion covers Allium cepa onions such as red, white, and sweet onions. It does not include spring onions (Allium fistulosum) or other species except when the Alliaceae (allium/onion) family is mentioned as a whole.
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Family | Container Size | Good Companions | Bad Companions | Soil Conditions | Germination | Sun | Water | Temperature Range | Height | Lifespan | Reproduction | Yield Per Plant | Ingestibility | Further Reading
What Family Do Onions Belong To?
Onions (Allium cepa) belong to the Alliaceae family, also known as the allium or onion family.
Some of their relatives include garlic, chives, and ramps.
What Size Container Should I Use for Growing Onions?
The minimum container depth recommended for onions is 6 inches.
A 5-gallon planter can hold 6-8 onions.
Learn more in our Choosing the Right Planter for Your Container Garden article here.
What Are Good Companion Plants for Onions?
Some of onions' best companions are as follows:
- Lettuce
- Chamomile
- Kale, broccoli, and other Brassicas
- Spinach
- Tomato
- Peppers like bell pepper and jalapeño
- Tomatillo
- Celery
- Lovage
- Carrot
- Peach
- Strawberry
- Rose
- Toothache plant
What Are Bad Companion Plants for Onions?
Onions are not compatible with every plant. Some things to avoid planting with onions are as follows:
- Pea
- Beans like green beans
- Sage
- Asparagus
- Squash
- Melons
- Cucumber
What Soil Conditions Do Onions Need?
Onions prefer fertile, well-draining soil that has a neutral to slightly acidic pH.
How Long Do Onions Take to Germinate?
Onions take 1-2 weeks to germinate at a temperature of 40-75°F.
How Much Sun Do Onions Need?
Onions prefer full sun.
Sun recommendations can vary by region, and onions grown in hot areas or in warmer conditions than the ideal temperature range noted below may need more shade.
How Much Water Do Onions Need?
Onions need 1 inch of water per week.
It is best to give onions the entire inch of water in one deep watering per week if possible.
What Is the Ideal Temperature Range for Growing Onions?
Onions grow fastest in temperatures of 55-75°F.
This is their ideal temperature range. Although they will grow in temperatures both cooler and warmer than this range, growth could be slower or even stunted.
Minimum and maximum temperatures will vary by variety. Some onion varieties are bred for autumn harvests and others for warmer climates.
How Tall Do Onions Get?
The average height of onions is 1-3 feet.
Are Onions Annual, Biennial, or Perennial?
Onions are biennial, meaning that their life cycle spans 2 years, and they flower, produce seed, and die in their second year.
How Do Onions Reproduce?
Onions reproduce by seed or bulb.
How Many Onions Are Produced Per Plant?
Onions produce 1 large bulb per plant.
Can Onions Be Ingested?
Onion bulbs and greens are edible.
Onion bulbs have antimicrobial and anti-inflammatory properties and can be used in herbal preparations. The most common preparations are broth and herbal honey. Though it is a less common preparation, an onion tincture can also be made using an herb:solvent weight ratio of 1:3 at 40% alcohol.
There are no known safety concerns associated with ingesting onion bulbs or greens.
Further Reading
This article is intended as a quick-reference guide for gardeners. Consult your seed packet or seed catalog for variety-specific information.
When you have a bumper crop of onions rolling in, you may not have enough time for long, complicated recipes or many-step preservation procedures. Check out my article on quick, simple uses for onions here!
Onions are featured in these Plant to Plate articles: