Growing Red Onions From Planting To Harvest

Red onions are one of the most common onion varieties used in culinary dishes aside from yellow onions. It’s a prized choice because of its mild, sweet flavor and gorgeous color, but too many gardeners shy away from learning how to grow and harvest red onions.

Red onions aren’t difficult to grow. Regardless of the type of onion that you grow, all onions are biennials, which means it takes two years to complete their life cycle. In the first year, the seed grows and forms tiny bulbs. Then, in the second year, the bulbs mature. 

  • Red onions grow best in loose, well-drained sandy loam.
  • Amend the soil with compost and granular fertilizer before planting for adequate nutrients. 
  • Sow red onion seeds indoors 8 to 12 weeks before the last average frost date.
  • Red onion plants need full sunlight, so pick a spot that receives six to eight hours of sun each day.
  • Make sure to water your red onions consistently; it’s recommended that you water once or twice per week in the morning.
  • You can harvest red onions when the leaves start to turn brown and wilt. Gently remove the mature bulbs from the soil.

Red onions are just as easy as yellow and white onions to grow. They don’t require any special treatment or care, so if you’ve grown one type of onion, you can grow them all. Let’s learn how to grow and harvest red onions in your garden this year. 

Red Onion Varieties to Grow

Before you learn how to grow and harvest red onions, you want to pick the varieties you would like to grow. Make sure to look at the days to maturity and compare it to how many days you have in your growing season.

Here are some popular red onion varieties.

Italian Torpedo

Italian Torpedo

This is a unique variety that has pinkish-red skins and an elongated shape. Italian Torpedo onions are a long-day cultivar that has a sweet, mild flavor. These onions take around 110 days to reach maturity.

Red Burgundy

Red Burgundy

Here is a short-day globe onion that produces three to four-inch bulbs with red rings and dark red skins. Red Burgundy is an heirloom onion with a mild and sweet flavor, and if you struggle with pink root disease, these onions are resistant.

Southport Red Globe

Southport Red Globe

If you want a storage red onion, try the Southport Red Globe. It’s an heirloom, long-day onion that produces large bulbs that have purple skins and pink flesh. These onions are ideal for Northern gardeners; they need around 100-120 days to reach maturity.

How To Grow Red Onions From Planting To Harvest

While onions are biennials, they’re hardy in USDA zones 5 through ten. You can grow red onions in the spring, summer, or winter in areas with mild climates. If you want to add red onions to your garden, here is our planting to harvest guide to red onions….

1. Amend The Soil For Onions

One of the keys to growing red onions is to give them a good start with the best soil possible. The soil should be well-draining; standing water will cause the bulbs to rot.

  • Mix two inches of compost into the soil first, which will give your onion sets the initial burst of nutrients needed to grow.
  • Mix an organic or time-release fertilizer into the soil before planting. The fertilizer should be under the planting furrow, which is called banding. You want the nutrients where the roots of the onion need them the most.
  • The soil should be between 6.0 to 6.8. You can test your soil using a pH meter to determine where your garden soil is.

To start your onion bed off properly, make sure you use a hard rake or hoe to loosen the soil. Remove all rocks and weeds as well. Root crops need loose soil to grow down into the ground.

2. Plant Them In The Right Spot

Red onions need plenty of sunlight to grow properly. They grow best when they receive six to eight hours of sunlight per day.

Look for a location that doesn’t have clay soil. If the spot you have available is clay, you’ll need to consider using raised garden beds or rows to create the fluffier soil.

3. Starting Red Onion Seeds

Growing red onions can be done either by growing seeds or growing red onion sets. While onion sets are easier, onion seeds are an economical choice for gardeners, but growing red onions from seeds takes plenty of patience.

  • Plant the red onion seeds indoors 8-10 weeks before your final frost date in your area. This is the time when you’ll set them outside. The seeds should be sown ¼ inch deep in their containers.
  • Onion seeds take four to ten days to germinate when started indoors, but they do grow slowly. You need plenty of patience.
  • When you transplant them outside, pick an open, sunny spot with fertile soil and proper drainage.
  • You won’t move these plants for two years, so be sure you space them correctly. Each onion seedling should be planted six inches apart.

4. Planting Red Onion Sets In Your Garden

Most gardeners prefer to plant red onion sets rather than starting seeds because it’s much faster. Remember, it takes a full year for the seeds to create a bulb. So, if you don’t use sets, you’ll wait two years to harvest; using onion sets helps you reach maturity faster.

  • Before planting, sort through your red onion sets and look for tiny ones or ones that look bad. The larger sets are preferred because they’ll grow better and produce larger bulbs.
  • Put each red onion set one to two inches deep; you want the roots to be well-covered, but the neck shouldn’t be set too deeply.
  • When you plant your sets, make sure it’s pointing upwards so that the shoot can grow above the soil.
  • Each little bulb needs to be spaced six inches apart, and the rows should be 12 inches apart.
  • Once all of your red onion sets are planted in the garden, you want to water your onions until they’re wet but not saturated.

How to Care for Red Onions

Red onions don’t require too much special care compared to other vegetables, but there are a few things you should remember about caring for these plants in your garden.

1. Consistently Water Your Red Onions

Red onion roots are shallow when compared to other vegetables, so they need a consistent supply of water. The roots are closer to the surface rather than deep down. If the top few layers of soil are dry, then it’s time to water.

  • Water your red onion plants once or twice per week. If the top three to five inches of soil are dry, then it’s time to water.
  • Red onions need around one inch of water per week.
  • Make sure you don’t overwater your plants. Overwatering results in fungus growth or bulb rot.
  •  The best time to water onions is in the morning; you want to avoid leaving your onions wet overnight.

2. Spread A Layer Of Mulch Over Your Red Onions

Spreading a layer of mulch around your red onions can help retain some of the moisture needed, which means you have to be waterless.

  • Once your onions sprout and you can tell where your rows are, try spreading a light layer of grass clippings around the onions. The mulch must stay off of the onion tops because they need full sunlight.
  • Laying out mulch also helps to reduce the weeds in your garden. Weeds compete with your red onion plants for nutrients.

3. Watch For Weeds

Weeds compete with your onion plants, so they’re a no-go in the garden. You need always to pay attention to weed growth because they will take away any nutrients in the soil that you added for your onions.

  • It’s recommended that you weed your onion patch once per week.
  • Running a hoe around your onions can also help to keep the soil free. Do this once a week as well.

How And When to Harvest Red Onions

Waiting all of the months to harvest your red onions can feel like an eternity, but it’s what you’ve been waiting for this whole time! You might start to wonder when to harvest red onions.

After a few weeks, you can pull red onion greens and use them as scallions in your recipes, but full-size red onion bulbs do take months to grow and mature. Depending on when you planted the sets, your red onion bulbs should be ready between late August and early October.

Red onions are ready for harvest when the bulbs are large, and the green tops start to yellow and fall over.

  • Red onions are ready to harvest when you notice around 10% of the tops falling over, it’s time to stop watering. At this point, you could harvest the onions or leave them in the ground to be gathered as needed.
  • Harvesting red onions is so easy! All you need to do is dig them up with either your hands or a garden trowel. When you’re picking red onions, be careful not to cut the bulbs, and then shake the soil off.
  • Lay the red onions out to cure with the tops still attached in a warm place with good air circulation. Setting them on a large screen works well! The onions must stay dry during this process.

As the red onions dry and start to cure, the roots shrivel up, and the necks dry. Curing takes seven to ten days.

At that point, you could either braid the tops for easy storage or remove the tops with shears and store them in a cool, dry place. Red onions store the best when in a location between 35-50℉.

Common Pests & Diseases That Bother Red Onions

While red onions might be easy to grow, that doesn’t mean they aren’t without their problems. Pests and diseases love onions, so you have to battle them back. Here are some of the most common pests and diseases that you might find in your onion patch.

Downy Mildew

One of the most common fungi that could bother your red onion plants is downy mildew. If your onion stems are constantly wet, the fungus can develop; it loves moist areas without much air circulation.

You’ll know that your onions have downy mildew because the stems start to turn grey and produce a strange, fuzzy growth. You can cut away the affected areas to save your plants.


If you find trails of holes throughout your leaves, you might have leafminers. Heavy infestations can result in white blotches on the leaves and the leaves dropping from your plant prematurely. An early infestation might reduce your yield.

Leafminers are a small black and yellow fly that lays their eggs on the leaves, and then the larvae hatch and feed on the leaves.

Ensure you remove your plants from your garden after harvesting so that they don’t have a space to grow and populate in the winter and spring. It’s best to avoid spraying with an insecticide until the infestation is heavy; you can try neem oil as an organic spray.


No one likes dealing with mites. They can cause your plants to have stunted growth, and the bulbs might rot in the ground or storage.

Mites are tiny pests, measuring less than one millimeter in length. They’re creamy-white, looking like small pearls with legs. It’s essential to take care of the problem because a mite infestation will make your plant vulnerable to pathogens and bacteria that could kill it completely.

Some people find that neem oil is an effective way to treat mite populations.

Onion Maggots

If you notice stunted or wilted seedlings, you might have onion maggots. These pests can cause the plants to break in the soil if you try to pull them out. If the infestation happens early, you’ll find that the bulbs are deformed and unable to store for long periods.

Onion maggot adults are a grey fly that lays white, elongated eggs around the base of your plants. The larvae that emerge will bore into your plants.

Managing onion maggots does rely on adequate sanitation; make sure to remove all onion bulbs at the end of the growing season because maggots use them as a food source in the winter. You can try insecticide sprays or use floating row covers when you plant the onions to stop the adult onion maggots from laying eggs on the plants.

Onion Neck Rot

Caused by the botrytis allii fungi, this is another common problem that onion plants experience. If you see a fuzzy, grey fungus growing on your onion’s head, you have onion neck rot. As it progresses, the onion’s head will rot and turn black.

It’s hard to treat onion neck rot once it sets in, but this is one reason why rotating your onion crops is essential. Make sure you always plant your onions in different places each year.

Pink Roots

If you find light pink roots that darken and turn purple, you have pink roots. Over time, the roots become transparent and water-soaked, and it might look like your plants have a nutrient deficiency. The affected plants might experience stunted growth.

The pink root is caused by a fungus that is absorbed through the root tips. It can live deep down in your soil. This disease is most severe when onions are planted in the same area continuously, so you must rotate your crops. You also can plant disease-resistant varieties.

Purple Blotch 

This fungus causes small, water-soaked lesions on the leaves or stalks of your plant with white centers. Over time, those lesions grow and turn brown to purple. Some of the larger lesions can kill the tissue between them, and severely infected plants will die.

This disease tends to pop up when the foliage continues to stay wet and the nights have high humidity. Gardeners need to make sure they don’t water in the evening and space the plants for proper air circulation.

You can try applying an organic fungicide if your plants have purple blotch, but it may not work. The most effective defense is rotating crops and letting them dry out during the day.

Growing Red Onions

If you’ve grown white onions, you can surely learn how to grow and harvest red onions. They grow and harvest the same, and they aren’t any more complicated than white or yellow varieties. Red onions have a  mild, sweet flavor that makes them an excellent addition to your garden.

Bethany Hayes

Written By

Bethany Hayes

Bethany is a suburban homesteader, growing over half of the vegetables, fruit, and herbs that her family of six needs each year. She raises chickens and homeschools her children. When she isn’t spending time tending to her garden, you can find her reading, crocheting, and canning.

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  1. Avatar photo Judy Sells says:

    This is good simple info that will help any first time gardener! I have a question. What if the ground freezes after you have planted your sets? If the tiny bulbs (sets) freeze with they still be viable ?

    I don’t want to plant them too early as we have a surprise freeze many years after beautiful weeks of spring weather.

    Thank you.
    Judy Sells
    east TN zone 7

    1. Onions can withstand light to heavy frosts and moderate freezes, but hard freezes can result in onion damage. We say that onion plants can survive temperatures as low as 20˚F, but what matters more is how long the temperatures are below freezing. Longer periods of freezing temperatures cause more damage to the plants. So, before a predicted freeze, water your onion plants and cover them with fabric or mulch to help prevent damage if you can. I recommend hay, mulch, grass clippings, etc. Moist soil, snow, and even ice act as insulation, holding heat in the soil around the bulb and root. Coverings further help by keeping the plants protected from the biting cold and wind.

  2. What does it mean when there’s a bulb forming at the top of the stem? Does this mean your red onion is ready to pick?

    1. When you notice a bulb forming at the top of the stem of a red onion, it typically indicates that the onion is starting to go to seed. Instead of focusing on bulb development, the plant redirects its energy towards producing flowers and seeds. While this can vary depending on the onion variety and environmental conditions, it generally means that the onion is reaching the end of its growth cycle.

      If you’re growing red onions for culinary purposes, it is ideal to harvest them before they start forming bulbs. Bulbing indicates that the onion is becoming mature and may not have the desired taste and texture for cooking. It’s best to harvest red onions when the tops start to turn yellow and flop over. At this stage, the onion bulbs are usually fully developed and ready for picking.