Growing Bunching Onions: A Simple Guide

Bunching Onions (Allium fistulosum) are versatile, hardy, perennial plants, commonly referred to as Welsh onion, Japanese bunching onion, long green onion, or spring onion. They share similarities with scallions but boast a distinct flavor profile.

Similar in taste and scent to common onions (Allium cepa), bunching onions can hybridize with them to form tree onions. Unlike common onions, they don’t produce bulbs, and their leaves and stems are hollow. Larger varieties, such as Japanese negi, resemble leeks, while smaller ones are similar to chives.

Bunching onions form perennial clumps and can also be grown ornamentally. The flowers are edible and tend to be somewhat dry in texture. They also share a similar pungent flavor profile with the leaves.

These plants are packed with essential nutrients, including vitamins A, C, and K, dietary fiber, and folic acid. Interestingly, the green parts of the onion boast higher concentrations of these vitamins than the white parts, making them a particularly nutritious choice.

Growth Characteristics and Lifecycle of Bunching Onions

Farm, Welsh onion, CC BY-SA 3.0

Bunching onions grow fast compared to other common alliums and are easy to cultivate. These plants can survive and produce for multiple years.

However, in temperate zones, gardeners cultivate them as annuals to maximize their yield and quality. Since bunching onions grow in clusters, they maximize space utilization and simplify the harvesting process.

While they prefer cooler climates, bunching onions exhibit remarkable adaptability to a wide range of temperature conditions. This makes them suitable for cultivation in diverse geographical locations. They grow best between 68°F (20°C) and 78°F (25.5°C), but can handle cooler temperatures and light frosts. This makes them good for early spring planting.

These plants are ideal for intercropping because their minimal root disturbance helps preserve soil structure and reduces erosion. They also naturally repel many pests, making them perfect companions in mixed-crop gardens.

Growing Bunching Onions

Plant your onions in early spring or late summer to promote optimal growth. This timing gives them a head start, allowing them to develop a strong root system before the growing season begins.

Sunlight

When choosing a spot for your bunching onions, look for areas that receive full sunlight. Bunching onions require a minimum of 6-8 hours of direct sunlight each day to thrive healthy. The selected spot should also have good air circulation. This helps minimize the risk of fungal diseases and promotes optimal plant growth.

Soil

To cultivate a healthy yield, choose a well-draining, slightly acidic to neutral soil (pH 6.0 – 7.5). Enrich the soil by incorporating aged manure or compost before planting. This amendment not only increases nutrient availability but also enhances moisture retention, creating ideal conditions for your crop.

Propagating Bunching Onions

You can easily propagate bunching onions from seeds, seedlings (transplants), or by division.

Seed Propagation

Choosing high-quality seeds from a reputable supplier is essential for growing healthy plants. Scientific studies have shown that these seeds typically boast germination rates above 85%.

To ensure a continuous supply of fresh onions and optimize your garden space, practice staggered planting. By planting seeds every two to three weeks, you can enjoy a longer harvest throughout the season.

Soak seeds for 12-24 hours in warm water, before planting to boost germination. Sow the seeds about ½ inch deep in rows spaced 12 inches apart. Water regularly and side-dress with fertilizer or compost. These plants have shallow roots and need consistent moisture.

Create a more controlled environment for your young seedlings by using row covers. This will shield them from harsh winds and pesky pests.

Seeds will begin to sprout, and the first shoots should appear in about 7-10 days. After that, leaves will grow rapidly within 20-30 days. The plants will then mature in around 35-40 days, allowing you to enjoy a continuous harvest.

Once the seedlings grow 2 -3 inches tall, make sure to thin them about an inch apart.

Succession Planting

To ensure a steady supply of fresh onions, plant a new batch of seeds every 3-4 weeks. This staggered planting approach allows you to enjoy a continuous harvest throughout the growing season.

You don’t have to wait for your bunching onions to mature before harvesting fully. Pull the entire plant or simply cut the leaves. The remaining bulb will regrow, providing another harvest in a few weeks.

To promote optimal growth, thin out crowded plants by removing some entirely, providing the remaining ones with more space.

Seedlings/Sets/Transplanting

You can also cultivate bunching onions from sets, which are the small onions typically found at nurseries in the spring. Any variety will do!  just be sure to harvest them before the bulbs begin to expand. This is especially important if you enjoy using green tops, which can be harvested throughout the summer.

You can start your own bunching onion seedlings indoors. Sow seeds in pots about 5-6 weeks before your last frost date. Maintain a consistent temperature between 59°F and 68°F, and keep the soil consistently moist until germination, which typically occurs within 7-10 days.

Once your seedlings reach 8-18 inches tall and are about as thick as a pencil, it’s time to harden them off. This process slowly helps your seedlings adjust to outdoor conditions. Expose them to increasing periods of outdoor light and temperature over several days.

Before planting, thoroughly water the dry soil. Once the soil is moist, you can lightly dip the roots of your seedlings into a liquid fertilizer solution before planting them. Plant the seedlings at the same depth as they were growing in their container. Place the plants 6 to 8 inches apart, leaving 12 to 18 inches between each row.

Separation/Division

Once established, these plants can be easily divided to spread around your garden or share with friends and neighbors! You can divide your bunching onions any time of year, but spring is ideal. To divide, simply dig up a clump, gently separate the roots into smaller sections, and replant them spacing apart.

Caring for Bunching Onions

Bunching onions are quite hardy. They can grow in almost any soil condition and tolerate some drought. However, for the best results, plant them in nutrient-rich soil, full sun, and water regularly.

Watering

Hydration is essential for the growth of bunching onions. These plants need about one inch (2.5 cm) of water per week, which can be supplied by rainfall or manual watering. During dry spells, ensure regular watering to keep soil moisture levels above 40% to prevent stress and stunted growth.

By using a soaker hose or drip irrigation system, you can conserve water and protect your onions from fungal diseases. These systems supply water directly to the roots, minimizing evaporation and leaf wetness while maintaining optimal moisture levels.

Fertilizing

Nutrient management is essential for growing healthy bunching onions. For best results, use a balanced, slow-release fertilizer. Ensure it has an N-P-K (Nitrogen-Phosphorus-Potassium) ratio of 10-10-10. Apply it when planting and again halfway through the growing season to encourage steady, robust growth.

For soils with lower fertility, apply a liquid fertilizer every two weeks. Always follow the manufacturer’s instructions to prevent damaging your plants with either excessive or insufficient fertilizer.

Mulching

This helps retain soil moisture, regulate temperature, and suppress weeds, all of which directly influence the growth rate and health of your bunching onions. 

To protect your bunching onions during winter, apply a thick layer of mulch around the plants in the fall. This will help them survive the cold and encourage early growth. You can also remove the mulch in the spring as the soil warms up, if there are no other problems like weeds.

Hilling

For longer, tender stalks, consider hilling your bunching onions. As the plants grow, gradually mound soil around the base, creating a small hill. This practice forces the leaves to grow longer and lighter in color, resulting in a more desirable harvest.

Harvesting Bunching Onions

Timing is everything when it comes to harvesting bunching onions. Typically, you can start harvesting the green tops when they reach 6-8 inches tall, about 60-70 days after planting.

At this point in growth, the onion tops are a rich dark green, and the bulbs remain small. For a milder flavor, consider harvesting a bit earlier. If you prefer a bolder, more robust taste, let the plants grow a bit longer. But don’t wait too long. As they over-mature, they lose their tenderness and become tough.

There are two ways to harvest your bunching onions:

Cut-and-Come-Again Harvest: Snip off the leaves as needed throughout the growing season. The plant will continue to produce new leaves, allowing for multiple harvests, throughout the growing season.

Whole Plant Harvest: Pull the entire plant from the ground and eat it like a green onion. To harvest your bunching onions this way, gently loosen the soil around the plant’s base with a garden fork or small trowel.

Then, grasp the plant by the leaves near the soil and carefully pull it out. If it’s resistant, try a gentle twisting motion to avoid breaking the stems or damaging the roots. Be mindful not to over-harvest your young plants, as this will allow them to develop strong roots for future growth.

Storing Bunching Onions

After harvesting, gently shake off any excess soil from the roots and trim away damaged or discolored leaves using clean gardening shears. You can enjoy freshly harvested yield, right away in your favorite dishes for the best flavor, or you can store them as mentioned below to use later.

Preserving

Bunching onions can be kept in the crisper drawer of your refrigerator for up to 10 days. For longer preservation, you can easily freeze them or dry them

Freezing

Step 1: Wash and Dry

Start by giving your greens a good rinse to remove any dirt or debris. Then, lay them out on a clean towel to dry completely.

Step 2: Chop and Pack

Once dry, chop the greens into your desired size. Whether you prefer thin or thick rings, it’s up to you!

Step 3: Freeze

No need for blanching! Simply pack your chopped greens into airtight containers, freezer bags, or glass jars. Label and date them for easy identification.

Ready to Use

Whenever you need a quick and easy addition to your meals, simply grab a handful of frozen greens and toss them right into your stir-fries, soups, or casseroles.

Drying

Drying is a popular method for preserving this plant, especially for those with abundant harvests. Its simplicity and effectiveness make it a great choice.

How to Dry Your Greens

Prep the Greens: First, wash your greens thoroughly to remove dirt or debris, then chop them to your preferred size.

Air Dry or Dehydrate: You can air dry your greens by spreading them out on a clean, dry surface. Alternatively, use a food dehydrator or place them in a low-temperature oven until they are completely dry and brittle.

Once dried, store your greens in airtight containers in a cool, dark place. They can last for several years, making them a convenient and long-lasting way to enjoy your harvest.

Companion Planting

Companion planting is a strategic technique that boosts the growing environment. Bunching onions emit sulfur compounds, which naturally repel pests, making them ideal partners for various garden vegetables. Below are some scientifically-backed combinations:

Carrots

Carrots and onions form a powerful alliance in the garden. Their strong scents work together to deter pesky pests. The pungent odor of onions masks the sweet scent of carrots, confusing root flies and keeping them away. Similarly, the carrot’s aroma can help to deter onion flies. By planting these two vegetables together, you can create a natural defense system that protects both crops.

Beetroots

Beets can benefit from the presence of onions in the garden. The strong scent of onions can help to deter beet leaf miners, tiny insects that can damage beet leaves. Planting onions near your beets can create a natural defense, protecting your crop effectively.

Tomatoes

Tomatoes and onions make a great gardening pair. The strong odor of onions can help repel aphids, tiny insects that can damage tomato plants. Planting onions near your tomato plants forms a natural barrier, offering protection for your crop.

Avoid These Plant Pairings with Bunching Onions

While bunching onions are generally good companion plants for many vegetables and herbs, there are a few plants that should be avoided:

Beans: Beans and onions are not compatible companion plants. The strong scent of onions can interfere with the nitrogen-fixing bacteria on bean roots, hindering their growth.  

Other Alliums: Avoid planting bunching onions too close to other alliums like garlic, leeks, and chives. While they are in the same family, they can compete for resources and may not be the best neighbors.  

It’s important to note that while these plants are not ideal companions for bunching onions, they can still be grown in the same garden as long as they are planted in separate beds or with sufficient space between them.

Common Pests and Diseases

Identification of Common Threats

While bunching onions are relatively hardy, they can still fall victim to various pests and diseases. Common risks include:

Thrips: These tiny insects feed on onion leaves, causing them to become distorted and discolored.

Onion Maggots: The larvae of flies, onion maggots’ tunnel into the bulbs, leading to rotting and decay.

Aphids: These sap-sucking insects can weaken your onion plants.

Damping-Off: This is a common fungal disease that affects especially young bunching onion seedlings. It causes the seedlings to rot and collapse at or near the soil line. The disease thrives in moist, poorly drained soil and warm temperatures.

Downy Mildew: This is a fungal-like disease that can cause significant damage to onions and other Alliums. Infected plants often show circular clumps of yellowed leaves, which can enlarge over time. The leaf tissue may turn pale green, then tan to brown or yellow, and eventually collapse. High Humidity, cool-wet weather conditions, etc., encourage this disease.

By staying vigilant against pests and diseases and implementing preventive measures, you can protect your bunching onion crop and ensure a bountiful harvest.

Prevention and Treatment

Pests

To keep your bunching onion crop healthy and thriving, it’s important to take preventive measures against pests. Here are some tips:

Garden Hygiene: Maintain a clean garden by regularly removing weeds and plant debris, as these can harbor pests.

Physical Barriers: Use row covers to protect your plants from flying insects like onion maggots. These covers create a physical barrier that prevents pests from reaching your plants.

Natural Predators: Encourage beneficial insects like lacewings and ladybugs in your garden. These natural predators can help suppress and control aphid populations.

By implementing these strategies, you can create a healthier garden environment and protect your bunching onion crop.

Diseases

To keep your bunching onions healthy, it’s important to prevent diseases like damping-off and downy mildew. Here are some tips:

Proper Watering: Avoid overwatering, as this can lead to waterlogged soil and create a breeding ground for diseases. Aim for consistent, moderate watering.

Crop Rotation: Rotate your crops annually to reduce the buildup of soil-borne pathogens. This helps to break the disease cycle and minimize the risk of infection.

While natural remedies are often preferred for treating pests and diseases, chemical treatments may be necessary for severe infections.

By following these practices, you can help ensure a healthy and productive bunching onion crop.

Quick Reference Guide

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