Skip to Content

How to Grow Red Onions: Growth and Care Guide

It is officially Spring. This is the best time to start planting your vegetable garden. Forget pesticide-covered vegetables or another trip to the grocery store. Sow your garden and reap the benefits of fresh produce outside your door. But before you start cooking your garden vegetables, you have to go through the growing process.

Having your vegetables grown from your garden can be quite rewarding. And red onions add flavor to any recipe. To learn how to grow and care for your future red onion harvest, read the instructions below.

What to Consider

If you are looking for vegetables ready for this year, red onions are a biennial plant, which means even though you may see onions after the first year, the second year will be the best year for harvest. This means it will take two years before you see full-growth red onions.

Climate Zone

To grow red onions, you must first determine if your climate is appropriate. If you’ve planted before, you will know that the hardiness zone or climate zone is an area set by the U.S. Department of Agriculture that designates where a plant naturally thrives. The climate zone is normally designated on the back of a seed package or the USDA website.

Red onions grow best planted in late spring in hardiness zones four through eight but can be planted in late winter in zones nine through thirteen. Most experts agree several hours of sunlight are needed for proper growth.

Most red onions do well planted in the spring season, but if you are in a mild climate, they can also be planted anytime between spring and early fall, only if the soil is dry for easy planting. Be sure to pick a sunny spot to plant your onions.

Where to Plant Red Onions

You can plant red onions in a garden if the soil is well-drained and a pH level between 6.0-7.0. If you do not know the pH level, you can buy test strips at a gardening store. These strips will come with instructions on how to properly use them. 

If you have denser soil or not enough space for a separate garden, you can use a raised bed or container. Whether planting in a pot, container, or windowsill planter, make sure each plant fits one per six to eight inches. 

For optimal growth, consider a planting area that receives plenty of sunlight and is drained well. The amount of sunlight hours the onions receive is important. The green stalks will grow tall in cooler temperatures, but the bulbs grow larger underground in warmer temperatures. So, the more sun, the better.

Here’s a helpful video of the onion growing process, with lots more info below:

What’s Next

Now that you have determined your climate and soil conditions are right for planting onions, you are ready to head to your local nursery and buy onion bulbs or seeds. Red onions are packaged in bulbs, seeds, or bulb sets, which look like small sprouted bulbs packed in planting trays.

Bulbs provide a faster full harvest, shortening the growth cycle sometimes by a full year. Also, bulbs require fewer planting steps. If you are considering seeds, keep in mind that seeds need more time to grow, so if it is late spring, stick with bulbs.

Other items you will need:

  • Compost and fertilizer. Soil mixes that already contain compost are available at nurseries and home improvement stores
  • If you are planting seeds, you will need small growing pots or a planting tray
  • Trowel or small shovel

Planting Instructions for Seeds

Here are the steps to planting red onions if you are transplanting your seeds, meaning you are planting the seeds indoors first and then moving them to the garden once germinated. This process is recommended for areas with short growing seasons.

  • In late February to mid-March, place your seeds in small growing pots or planting trays according to the package directions. Typically, this is six to eight weeks before planting outside.
  • If directions are not available, spread the seeds one-half an inch apart and then cover with one-fourth an inch soil. If you are using a planting tray, place three seeds in each cell spaced out throughout the cell.
  • Once the tops reach four to five inches tall, transplant the seedlings to the garden, spacing four inches apart.
  • In your garden, use a small trowel or hand rake and dig to a six-inch depth. The soil should be tilled so that the soil is loose.
  • Mix two inches of compost into the soil. The soil should be airy or fluffy.
  • Set the red onion seedlings root-side down into the soil (The root is the small end of. Each seedling should be placed one inch deep and two to four inches apart.
  • Cover the seedlings with soil, and keep the soil loose.
  • If you are planting multiple rows, space the rows twelve to eighteen inches apart.
  • Water the soil once you are done planting.

When your soil is prepared for planting, usually April or early May, you can place the seeds directly in the ground without transplanting. If you are directly seeding into your garden:

  • Place about two seeds per two inches, at one-fourth to one-half an inch depth. The rows of seeds should be twelve to eighteen inches apart. For larger onions, seeds should be three to four inches apart.
  • Cover with one-fourth to one-half inch soil. Do not compact the soil.
  • Water the soil once you are done planting.

Planting Instructions for Bulbs

You are ready to plant red onion bulbs two to four weeks before the last frost.

  • Using a small trowel or hand rake, dig to a six-inch depth. The soil should be tilled so that the soil is loose.
  • Mix two inches of compost into the soil.
  • Set the red onion bulbs root-side down into the soil. Each bulb should be placed one inch deep and two to four inches apart. If your bulbs come in a set, you will need to separate them by gently removing the soil surrounding the root and plant them individually.
  • Cover the bulbs with soil, and keep the soil loose.
  • If you are planting multiple rows, space the rows twelve to eighteen inches apart.
  • Water the soil once you are done planting.

How to Take Care of Your Onions While Growing

Whether you planted bulbs or seeds, keep the soil well-drained for optimum growth. Regularly water the plants one to two times per week. Watering is needed if the top three to six inches of the soil are dry. Check regularly for weeds and hand remove weeds to make sure your onions are not competing for growth space. 

You can also use fertilizer three weeks after planting. Place a slow-release fertilizer two to three inches beside the row of onions. Work the fertilizer into the soil, then water. Consult the fertilizer instructions to make sure the correct amount of fertilizer is used for your space.

After about a month, natural rain should be able to keep your onions hydrated but check weekly to make sure your onions are getting enough water.


When growing starts, stems will appear, called modified leave, forming above ground. These stems then form longer necks, which are green onions. Thinning a few of these green onions out may help with bulb growth, and the thinned out green onions can be cooked and eaten just like the ones sold at grocery stores. 

The onions are ready to be pulled out of the ground when the necks become soft and start to fall over. Too much time in the ground may cause fungus, mold, or decay. This takes five to seven months. 

Every onion stalk that appears should be pulled the first year. This gives the other onions left in the soil room to grow. Once you pull the bulb out of the ground, gently knock off any extra soil from the bulb. The bulbs may seem smaller than what you are expecting, but remember, it will take two years to see full growth.

Ideally, pulling the onions in the morning is the best time so that the onions can be left in the shade to dry throughout the day. Dry onions for two to seven days if the weather is dry. If it rains, you can move the onions to a dry and covered space.

Drying the Onions

Curing or drying the onions is the next step after harvesting. Once pulled, onions can be dried outside in the sun for a week, then moved to a cool, shady, and well-ventilated space for another week. Or, onions can stay in a cool and shady space for two weeks or until completely dry. Onions can also be set on newspaper to dry.

To save drying space, you can braid the stalks together and hang the bunches to store in a cool, dry, and ventilated area. Onions can be stored for up to three months. 


Although planting any vegetable may seem intimidating, if you follow a few guidelines, you should have success. Remember, red onions take two years to see full growth, so do not be disappointed with the size after the first year. But do be sure you have this time to devote to your garden.

A general awareness of the climate you are gardening in, and the weather will help you plant at the right time and for plants that will thrive in your garden. Don’t wait until it is too hot to plant. Plant in early spring, and be aware that it takes five to seven months before the onions are ready for harvest.

If you tend to your garden once you plant your onions, by making sure your onions are well-drained, watered regularly, and hand weeded, you should see great-looking onions at full harvest. And remember, be sure to completely dry your onions in a shady, cool, and well-ventilated area for at least two weeks before you start using them in your cooking.

Sharing is caring!