Seed Swaps


Allium cepa var. cepa

'Onion' is a plant in the Allium genus with a scientific name of Allium cepa var. cepa.

Onion can be grown from seed or from sets and is a popular mainstay of vegetable gardens around the world. This species produces a large, round pungent scented bulb that can be used for a variety of different culinary uses and can be brown, pink, yellow red or white in colour.

In general, onions tend to be grouped into two major categories: long-day or short-day. These groupings indicate the day length required for the bulb to start to form – if the day length of the area is too short for the variety of onion, small, stunted bulbs will result – so it is important to plant at the optimum time and choose an appropriate variety for your area.

Blooms appear in these approximate colours:   Dark pastel purple and   Purple mountain majesty and   Purple taupe. When mature, they grow to 6.0 cm (2.34 inches imperial) in diameter. The mature flowers are of a pompon form. Leaves appear approximately as a   Ao green and   Dark spring green

Onion grows as a biennial and is a flowering edible vegetable / flower. Being a biennial plant, it tends to grow best over the course of two years.

Onion is known for growing with a forb habit to a height of approximately 45.0 cm (that's 1.46 feet in imperial). This plant tends to bloom in early summer, followed by first harvests in early autumn.

Try planting Onion if you'd like to attract bees to your garden.

Popular varieties of Onion include: Red, Yellow, Walla Walla Sweet, White and Yellow Sweet Spanish.

Onion is normally quite a low maintenance plant and is normally very easy to grow - great for beginner gardeners!

This plant info is provided by the myfolia gardener's wiki. All details about Onion have been kindly provided by our members.

How to grow Onion

  • Full Sun

  • Partial Sun

  • Medium

Keep onion sets free from weeds as grass and weeds tend to compete for nutrients and moisture. Side apply fertiliser during the season if need be.

Try and keep the moisture levels in the soil as consistent as possible – applying mulch is often a good idea. This reduces bolting

Plant in a location that enjoys full sun / partial sun and remember to water moderately. Zone 3 to 10 are typically the USDA Hardiness Zones that are appropriate for this plant (although this can vary based on your microclimate). Ideally plant in loamy, clay and sandy soil and try to keep the ph of your soil between the range of 6.0 and 7.0 as Onion likes to be in weakly acidic soil - neutral soil. Keep in mind when planting that Onion is thought of as hardy, so this plant will grow or become dormant during the winter.

See our list of companion Plants for Onion to see which plants you should plant in close proximity to encourage growth.

Growing Onion from seed

Growing onions from seed can be trickier than growing from established sets, but it is possible, and can often produce more disease resistant plants.

Sow into flats in a soilless medium and keep in a warm place for about a week to germinate.

Sow at a depth of approx. 0.98 inches (2.5 cm) and aim for a distance of at least 1.95 inches (5.0 cm) between Onion plants. Soil temperature should be kept higher than 13°C / 55°F to ensure good germination.

By our calculations*, you should look at sowing Onion about 28 days before your last frost date .

Transplanting Onion

Onions are often transplanted from sets – this is typically the quickest and most foolproof strategy to grow onions as growing from seed can be problematic. Sets (or bundles) can be purchased from garden stores and over the internet, and typically contain around 60 – 80 plants.

Onions can be planted out as soon as the ground can be worked in the spring. If you are growing to harvest as green onions, seedlings can be planted quite close together as they will be harvested before they reach full size. If growing for mature dry onions, try to plant as far apart as practicable and thin and use as green onions as you go if you misjudge the distances initially. Keeping good distances between plants is very important for achieving good onion bulb size.

Ensure that temperatures are mild and all chance of frost has passed before planting out, as Onion is a hardy plant.

Harvesting Onion

Harvest onions when the tops turn yellow and begin to topple over. To dig them up, loosen the soil around each bulb and then lift them up carefully – make sure not to damage as they can rot quickly.

Spread them on a flat surface above the ground and leave to dry out – this will take anywhere from 2 to 10 days if left out side, or 2 weeks if taken inside. Cut the tops, and then store in mesh bags in a cool, well ventilated space. Alternatively the dry leaves can be platted and the bulbs made into a decorative onion string for storage

Seed Saving Onion

Onion seeds can be saved by carefully cutting off the flower head (floret) when the seeds have fully developed, and then placing in a paper bag in a cool dry location for a couple of weeks.

How long does Onion take to grow?

These estimates for how long Onion takes to sprout, grow and harvest are from real observations from real gardeners, right around the world.

Start logging and journaling your observations to participate!

Days to Germination How long does it take Onion to germinate?
10 days

Average 10 days | Min 1 days | Max 28 days (675)

Days to Transplant How long until I can plant out Onion?
+ 45 days

Average 45 days | Min 4 days | Max 120 days (164)

Days to Maturity How long until Onion is ready for harvest / bloom?
+ 117 days

Average 117 days | Min 16 days | Max 230 days (337)

Total Growing Days How long does it take to grow Onion?
= 172 days

When should I plant Onion?

Our when to plant Onion estimates are relative to your last frost date.

Enter your frost dates and we'll calculate your sowing and planting dates for you!

When to sow The number of days to sow Onion before or after your last frost date.
28 days before Last Frost Date

Onion Etymology

The common name of “Onion” is probably derived from the Latin unus, meaning “one.”

Onion Folklore & Trivia

  • Onion is said to relieve the pain of dog bites and toothaches.
  • The Romans are said to have brought the Onion to England.
  • Growing onions in warmer climates tends to produce sweeter tasting onions.

The flavonoids are concentrated on the outer layers of the onions, so peel as little as possible of the edible portion when removing the outermost paper layer.

Eating several servings of onions each week may be sufficient to lower your risk of some types of cancers. For colorectal, laryngeal, and ovarian cancers between 1-7 servings of onions has been shown to provide risk reduction. For decreasing your risk of oral and esophageal cancer, you’ll need to consume one onion serving per day (approximately 1/2 cup).2

Herodotus (~485-425 BC) wrote that the builders of the ancient Egyptian pyramids were paid in radishes, onions and garlic3.

Other names for Onion

Garden onion, Common onion, Cebolla

Allium cepa Cepa Group, Allium cepa (Cepa Group)

Misspellings: Oignon, ognion, Allium capa, Onions

Latest Onion Reviews

  • First grew these a couple of years back and produced brilliant, huge bulbs. Hope they grow as well again this time around!

    5 stars

    leafykitti about growing Onions
  • First onion I’ve grown from seed. I had 1-2 inch bulbs at the end of the season. I started them inside as well as direct seeds them and did not notice much of a difference.

    3 stars

    Kazedwards about growing Ailsa Craig 1

See all Onion reviews and experiences »


1 Cass County Extension

2 Onion-The world’s healthiest foods

3 :The Encyclopedia of Medicinal Plants: A Practical Reference Guide to over 550 Key Herbs and Their Medicinal Uses; Andrew Chevallier; published 1996

Onion Forums

  • Garlics, onions, chives, etc.

    If you grow any plants that are in this group, this is the group for you!! Find out how to plant, grow, nurture, and...

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