How to Plant, Grow, and Care for Red Onions

Red onions are a magical ingredient. They give salads and sandwiches a satisfying spicy crunch. Curries and chutneys wouldn’t be the same without them. And red onion pickles? Don’t get me started!

As versatile as they are in the kitchen, these tender bulbs are equally easy to grow in the garden. They’ll stand up to almost any climate, and novice gardeners can enjoy their easy maintenance and bountiful harvests. 

They’re some of the oldest and most widely used vegetables on earth. The red variety evolved over thousands of years from species of wild onions. Humans have cultivated them since ancient times. In India, the first record of their use dates back 5,000 years and in ancient Egypt, to 3500 B.C.E. 

The red color of these onions comes from anthocyanin pigments in their skin. These natural dyes have powerful antioxidant, anti-inflammatory, and cardioprotective properties. These bulbs also contain a huge amount of vitamins and minerals. Because of this, these allium varieties are incredibly important in a healthy diet. 

Characteristics

Red onions are biennial but often grown as annuals. You can harvest them around 110 to 115 days after sowing. 

They grow large and flavorful green foliage around their bulbous base. The leaves are hollow and can grow up to 2 feet tall. 

Every part of the plant is edible and highly nutritious for humans. However, they may be toxic to pets such as dogs, horses, and cats. 

Native Area

Red onions evolved from wild onions in Central Asia, similar to white onions and other species in the Allium genus. Ancient societies propagated them for their red color, and soon, they spread throughout the ancient world. 

From ancient Egypt to ancient China, these delicious bulbs became mainstay ingredients in a variety of cuisines. People then brought them to the Mediterranean region where they took hold in Greece and Rome. Pliny the Elder wrote about them and the ancient Greeks used them as a dietary supplement. 

After spreading throughout Europe, these red-skinned bulbs made it across the pond to the Americas. Today, these flavorful crops grow all over the world and are some of the most widely consumed vegetables on the planet. 

Planting

You can grow healthy plants from seeds, bulbs, or transplants. Seeds are a little harder to grow, but they are cheaper. All you’ll need are the right growing conditions and healthy seeds under a year old. 

Plant your sets in early spring, just before the last frost date. Once you can work the soil in your garden, you can get them in the ground. These vegetables are cold hardy and don’t mind a little frost. 

Find an area with full sun and rich, well-drained soil. Place each immature bulb or ‘set’ into the soil about 1 or 2 inches deep. Keep the rows over 1 foot wide and space your sets apart by around 6 inches. This will encourage aeration and prevent harmful fungal infections from forming in cramped growing conditions. 

Transplanting

If you have transplants, get them into the ground as soon as you can work the soil. As mentioned before, find an area with rich, well-drained soil that’s nice and loose. Dig trenches a few inches deep. 

Harden off indoor transplants over the course of a week before planting. After this, remove them carefully from their containers and gently remove excess soil. Plant them up to their crowns and space them out roughly 4 to 6 inches apart. 

After transplanting, give them a good amount of water. Make sure the soil stays nice and moist as they grow. Amend the soil with an organic compost after transplanting to give your vegetables extra energy. 

Growing From Seed

Choose young, healthy seeds from reputable companies. Inspect the seed packets ahead of time, or rely on honest reviews from fellow gardeners. The best plants always start from the best seeds. 

Start seeds indoors 10 to 12 weeks before you expect your last frost. Plant the baby onions at a depth of ¼ inch. Plant 2 or 3 seeds per hole and space them out about 4” apart. Once they grow, thin them out to around a half-inch apart. 

You can also directly sow them outdoors 4 to 6 weeks before the last frost is expected. Make sure the soil is loose and full of organic material. Wait until your soil is at least 45°F (7°C) before planting. 

Growing From Sets

Sets are immature bulbs meant for planting. You can find them online or at your local nursery. Although they’re easier than seeds to grow, you’ll miss out on the wonderful varieties that seed growing provides. 

Plant your sets in raised beds with loose, well-drained soil. Add plenty of compost before you begin. Make sure your beds are at least 15 inches deep. 

Place them around 1 to 2 inches deep in the soil and cover them. If you’re working with very immature sets, covering up to the base of the stalk is perfect. For those with substantial bulbs, keep the top poking out of the soil. Make sure they’re at least 4 to 6 inches apart, or they’ll grow too congested. Give them plenty of water after planting and make sure the soil stays moist but not waterlogged. 

If you grow them indoors, use indoor grow lights or plant them near a south-facing window. Onions won’t thrive without enough light, so avoid planting them in the shade. 

Your latitude will determine how successfully your plants will grow. Some varieties are short days while others are long days. Long-day onions need up to 16 hours of sunlight during their growing period. Short-day onions need between 10 to 12. 

When you buy your seeds or starters, select varieties according to their day type and where you live. Long-day onions thrive in northern climates, while short-day varieties do better closer to the tropics. 

Water

These aromatic vegetables need plenty of water throughout the growing season. They have shallow roots so you’ll have to keep the topsoil moist as they grow. 

If you’re growing your vegetables in raised beds, consider installing an irrigation system. This will save you a lot of time and energy and help your plants to thrive. 

Soil

Red onions thrive in well-drained soil that is high in organic material. Test your soil to make sure it has a pH between 6.0 and 7.0. A slightly more basic pH of 8.0 is also sufficient.

Amend the soil with plenty of compost and manure to increase its nutrient content. These plants are heavy feeders and thrive with extra nutrients. 

Temperature and Humidity

Alliums, in general, can tolerate cold temperatures when you plant and harvest them. They’ll thrive in a variety of climates as long as they get enough light and have nutritious soil. 

High heat can damage many varieties. Most prefer to grow in cool conditions below 80°F (27°C) during the peak of summer. Growers in hotter climates should choose long-day varieties.

Light freezes and snowfall will be no match for your plants. However, temperatures below 20°F (-7°C) can quickly damage their leaves. 

Fertilizing

As soon as you transplant your seedlings, give them a high-phosphorus organic plant food. Look for an NPK label of around 10-20-10. 

Gently add the plant food around the soil, but don’t get it near the plants. Water thoroughly to avoid fertilizer burn. 

Maintenance

These hardy vegetables are easy to maintain with a few simple tasks. First, cover your beds with tarps before planting to kill any weeds in your beds. 

You can also trim the tops of transplants before planting to give them a quick energy boost. Other than that, simply follow basic garden maintenance, and you’ll enjoy healthy plants throughout the growing season. 

Propagation

You can propagate red onions from seeds or from sets. Either method works well, yet seeds will give you more varieties to choose from. 

If you let your onions go to seed in the fall, collect the seeds when the seed heads turn dry and brown. Dry the seeds in a cool, dark place in a paper bag. Wait several weeks until they’re fully dry before storing them for the following season. 

If you harvest immature sets, store them in a cool, dry place until the next growing season begins. Keep them in breathable mesh bags away from light and water. 

Harvesting and Storage

Harvest your onions roughly 90 to 130 days after sowing. Stop watering once you notice the leaves lose their shape and vertical growth. When you see the stems turn brown after a week or two, your bulbs are ready to harvest. 

Gently remove your bulbs from the soil, dust off the dirt, and let them cure in a dry place for a few weeks. Once their tops are completely dry and their skin feels like paper, they’re perfectly cured. 

Keep them in an aerated area with low humidity and light. They should last for several months. 

Common Problems

These biennial plants are easy to grow, but they do have a few problems. First, they need full sun. Many gardeners, myself included, have had problems getting big, juicy bulbs to grow. This is usually because we planted the wrong variety for our location’s day length. 

Excessive heat and environmental changes can also stress your plants out. Make sure to transplant and harvest during cool days when the plants are not experiencing stress from heat. 

Pests

All species of Alliums suffer from a few common garden pests. One of the most prevalent is the onion maggot. This pest will bore itself into the bulbs and stems, causing damage to the plant’s structure and health. Other pests include common aphids, thrips, and leaf miners. 

To prevent these pests, it’s important to keep a healthy ecosystem in your garden. Encourage beneficial insects like ladybugs and wasps with a diverse array of flowering plants. The more birds you have in your garden, the better. 

Diseases

The most common diseases to watch out for are rots. Look for signs of fusarium basal rot, bacterial soft rot, and botrytis neck rot. To prevent these diseases, always water your plants in the morning or from the bottom with proper irrigation. Space them out and give them plenty of aeration as they grow.