5 Steps For Growing Onions From Sets, Transplants, or Seeds

Learn how to grow onions (including planting onions and harvesting onions), by following the guidelines below. Onion is fairly easy to grow...just ensure that you have the right "day" variety for your area.

How to Grow Onions - Onion Varieties

The formation of nice bulbs is very dependent on the amount of light that the onion plant receives. Growing onions is best accomplished by choosing the right variety for your geographical location.

Long-day Varieties

Long-day varieties of onion are best grown in the North. They require ~14 hours of daylight or more per day. (Onion Variety: Yellow Globe Danvers, Sweet Spanish, Yellow Flat Grant, Yellow Rynsburg, Zittan Yellow, Wala Wala Sweet, White White, Snow White Hybrid, Red Delicious). Long-day onions usually store well.

Short-day Varieties

Short-day varieties of onion are best grown in the South, where there is 11-13 hours of daylight. (Onion Variety: Yellow Bermuda, White Creole, White Granex, Eclipse, California Early Red, Ebenezer, Early Strasburg, Giant Red Hamburger, Salad Red.)

Intermediate-day Varieties

Growing onions that require 13-14 hours of daylight belong to the group in between called intermediate-day varieties. (Onion Variety: Australian Brown, Early Yellow Globe, White Portugal, Southport Yellow Globe, Italian Red, Red Wethersfield, Southport Red Globe, Flat Madiera.)

How to Grow Onions - Important Considerations


Onions are a member of the Allium family. Growing onions is best accomplished in soil that is moist and fertile, and in a sunny location. Onion can been grown in the same garden location for several years, so it is important to carefully prepare the bed to be rich in nutrients and have good drainage. 

Approximately 2lbs of well-rotted manure/compost should be worked in to every 5 feet of row. An alternative is to use 1/4 lb of 5-10-10 fertilizer for every 5 feet of row.

Planting Onions from Seeds, Transplants, or "Sets"

Onions can be planted outdoors by seed, transplant or "set" (small bulbs from the previous year). The time to maturity (3-5 months), is shortened by 4-6 weeks if transplants or sets are used. To grow seedlings indoors, plant 4-6 weeks before the average last frost. "Sets" provide the easiest and most disease free method of growing onions. To grow from "sets", bulbs should be less than 1/4 inch in diameter so they do not bolt before producing edible onions.

Watering and Weeding

When learning how to grow onions, it is important to keep in mind that onions cannot compete well with weeds...so stay on top of removing weeds from around the onions. When watering, try to give water directly to the growing onions and not the weeds! Onions require approximate 1 inch of water per week. Be careful that the bulbs do not dry out, or they will split.

Planting Onions - When and How

From Sets or Transplants

  1. Begin growing onion transplants 10-12 weeks before your final frost. Plant seeds 1/4 inch deep.
  2. You can start planting onions outdoors from sets/transplants as soon as the ground can be worked, or 3-4 weeks before your final frost.
  3. Trench a 4 inch deep furrow and water to moisten the soil.
  4. Place each bulb 1 inch deep, 4 inches apart, in rows that are spaced 1 foot away from each other.
  5. If you are planning on harvesting younger plants as green onions, plant closer together (~2 inches apart).

Planting Onions From Seed Outdoors

  1. Plant seeds about 1 inch apart, and 1/2 an inch deep.
  2. When seedlings are 3-4 inches tall, start thinning them out so that the seedlings are 2 inches apart.
  3. When they reach 6 inches tall, then them again so that the spacing is 4 inches.


You should not have to fertilize during the growth of the onion plants if you hvae prepared your soil well. If need be, the growing onions may benefit from fertilizer once they are 8-10 inches tall. Spread ~1/2 lb of 5-10-10 for every 25 feet of row, on both sides of the onion rows. Try to mix in with soil, but be careful to not disturb the roots.

Harvesting Onions

The reward for learning how to grow onions is the harvest at the end. Globe onions are ready ~5 months after the seeds have been planted, or 3 1/2 months after planting seedlings or sets. You will know that the onion plants have reached maturity when the tops begin to fall over. The tops will also turn yellow/brown and at this point they can be tipped over to speed up maturation and produce larger bulbs.

After two weeks, or once more than half of the tops have tipped over, pry up the bulbs with a spade fork so that they lie in loosened dirt. Within another week or two, lift the bulbs out and either leave the tops for braiding later, or cut the tops off leaving 1 inch. Dry the onions in a warm place away from the sun until the outside of the onions is dry. At this point they can be braided and hung, or stored in mesh bags. Store in a cool, slightly humid location. They can be stored for up to a year.

How to Grow Onions - What Can Go Wrong

When growing onions, there are a few things that can go wrong. Onion maggots can infest your plants and are almost impossible to stop. They burrow through the bulg and feed upwards. Other pests include thrips which will cause mottling and withering plants.

The best defense against these pests is to (1) Plant onions in various locations around the garden (other plants will benefit: see companion planting), (2) Keep a clean garden; thrips live in weeds from previous years, and (3) rotate your crops at least once every three years.

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