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How to Plant and Grow Onions

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Onions are easy to grow in the home garden and make a perfect flavor enhancer for both raw and cooked recipes. The green tops are edible and the bulbs store well and can be kept for months after harvest.

Onions take up very little space in the garden and are a cool-season vegetable, so there is nothing not to like about this root vegetable. Use these tips and grow some fresh onions in your garden this spring.

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How To Start Onions From Seed

Starting onions from seed is the most economical way to grow this tasty crop. Onions need 90-100 days to reach maturity and starting the plants from seeds will help ensure they have plenty of time to reach maturity.

  • For starting onion seeds, use a growing medium that contains peat, perlite, and vermiculite. This will ensure good drainage and plenty of soil nutrients. You can mix one yourself or purchase a seed starting mix to save time.
  • Fill a seed tray or shallow pan with the growing medium and moisten it.
  • Place 2 seeds in each seed pod or space seeds in an open tray 2 inches apart. Mist with room temperature water and cover with a plastic dome lid or plastic wrap.
  • Place seed tray in a bright, warm location. Remove the plastic lid or plastic wrap at the first sign of germination (5-10 days). Place seeds tray in a location that receives direct sunlight for several hours each day.
  • Keep soil moist at all times. When seedlings are 5-inches tall, snip the stalks back to 2-inches to make them stronger and produce larger onions.
  • After all danger of frost has passed in the spring, onion plants can be transplanted into outdoor soil.

How To Start Onions From Sets

Growing onions from sets is easier for beginner gardeners or those just wanting less seed starting. Purchase onion seed sets from a reputable gardening shop. Then proceed as follows:

  • Wait until all danger of frost has passed
  • Work 2-inches of compost into the soil and create shallow rows that are 1-inch deep and 10-inches apart. (Want to start composting? Check out my how to start composting guide.)
  • Place 1 onion every 4-inches into the rows. Pointy side up.
  • Pull soil over the onion set and tap done gently. 
  • Water thoroughly.

Soil Conditions for Growing Onions

Onions grow best in loose, loamy soil that has a pH of 6-6.8. They don’t like heavy clay soil or soggy soil conditions. Before planting, have your soil tested if possible. Learn how to improve your garden soil, which includes getting a soil sample analyzed.

Onions grow equally well in containers, raised beds, or in-ground. So, if you’d like to give them a try this season, consider growing them in a container as a test run!

Blooms on onion plants

Watering and Fertilizing Onions

Once onion plants or sets are planted, how should you care for them?

  • Place a 2-inch layer of mulch around onions to prevent the tops from being exposed to sunlight and to prevent weed growth.
  • Water deeply during times of drought.
  • Feed onions every 3-weeks with a high nitrogen fertilizer. (I like to use Espoma for most of my fertilizer needs.)

Folding Down Onion Tops

The first year I grew onions in the garden, I had no idea what I was doing. The long tops were almost as tall as my shoulder, and the blooms were so pretty.

However, after that first year, I received tips from several readers about folding down the tops of the onions before harvesting them. Many gardeners roll or fold onion tops down to halt the onion from taking up water, thus preparing them for harvest.

If you’re going to fold your onion tops down, do so when the tall green growth begins to yellow and some begin falling over on their own. Roll down onion tops several days before harvest.

When To Harvest Onions

Depending on where you live and when onions were planted, many are ready by mid-summer much like garlic. When the tall green tops of the onion plants will begin to flop over, this is a signal that onions are ready to be harvested.

Onion blooms are also a good sign that the plants are just about done growing.

Use a sharp spade to dig down under the onion and lift it out of the soil at harvest time.

How to Dry and Cure Onions

Once onions are harvested, they need to dry out for a few days, much like garlic. Lay onions out in a single layer on the ground when weather is expected to be warm and dry.

Onions drying out beside our raised bed

If you’re planning to use the onions pretty quickly, then don’t worry about curing. Bring the onions in and use them up. Or as I learned from a NC onion farmer last year, put whole onions in a freezer gallon bag and freeze them. (You could also chop them ahead of time and freeze in easy one-cup measurements for recipes.) See the full article about Eastern NC Onion Farming.

For curing onions for longer storage, lay them out in a dry, well-ventilated area, away from direct sun for 3 weeks. Once the outer skins have become papery, store the onions in a cool place with good ventilation, such as a paper bag or a basket.

Yield: N/A

How to Plant and Grow Onions

onions growing in a field

One of the easiest crops to grow in the home garden is onions! Learn how to grow onions at home whether starting from seed or sets.

Prep Time 30 minutes
Active Time 30 minutes
Additional Time 2 months 24 days 4 hours
Total Time 2 months 24 days 5 hours
Difficulty Easy

Materials

  • Onion seeds or sets
  • Compost
  • Fertilizer

Tools

  • Trowel or Spade
  • Watering Can or Hose

Instructions

To start onions from seeds:

  1. For starting onion seeds, use a growing medium that contains peat, perlite, and vermiculite. This will ensure good drainage and plenty of soil nutrients. You can mix one yourself or purchase a seed starting mix to save time.
  2. Fill a seed tray or shallow pan with the growing medium and moisten it.
  3. Place 2 seeds in each seed pod or space seeds in an open tray 2 inches apart. Mist with room temperature water and cover with a plastic dome lid or plastic wrap.
  4. Place seed tray in a bright, warm location. Remove the plastic lid or plastic wrap at the first sign of germination (5-10 days). Place seeds tray in a location that receives direct sunlight for several hours each day.
  5. Keep soil moist at all times. When seedlings are 5-inches tall, snip the stalks back to 2-inches to make them stronger and produce larger onions.
  6. After all danger of frost has passed in the spring, onion plants can be transplanted into outdoor soil.

To start onions from sets:

  1. Wait until all danger of frost has passed
  2. Work 2-inches of compost into the soil and create shallow rows that are 1-inch deep and 10-inches apart. (Want to start composting? Check out my how to start composting guide.)
  3. Place 1 onion every 4-inches into the rows. Pointy side up.
  4. Pull soil over the onion set and tap done gently. 
  5. Water thoroughly.

Watering and Fertilizing Onions

  1. Place a 2-inch layer of mulch around onions to prevent the tops from being exposed to sunlight and to prevent weed growth.
  2. Water deeply during times of drought.
  3. Feed onions every 3-weeks with a high nitrogen fertilizer. (I like to use Espoma for most of my fertilizer needs.)


To Harvest Onions


Onion blooms are a good sign that the plants are just about done growing.

To harvest, use a sharp spade to dig down under the onion and lift it out of the soil at harvest time.

Dry, cure, and store as needed.

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