Understanding 4 Onion Growth Stages: Germination to Bulb Formation and Maturation

Updated: 19 Feb 2024


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An onion is a vegetable in the Allium family. It is characterized by its distinctive layered structure and pungent flavor. Onions are grown worldwide and used in various dishes, including salads, soups, stews, and stir-fries. Onions are rich in nutrients, including vitamins C and B6, and are also a good source of fiber and antioxidants.

They are known for their anti-inflammatory and antimicrobial properties and have been shown to have potential health benefits, including reducing the risk of certain types of cancer. This blog post explores all onion growth stages, from germination to maturation.

Onions growth stages
Onion growth stages

Introduction of Onion Growth Stages

Onions have four growth stages: seed germination, seedling, vegetative growth, bulb formation, and maturation. The seed absorbs water and swells during germination, breaking through the seed coat. In the seedling stage, the onion plant grows leaves and a stem, with the first bulb forming below the soil. As the bulb grows, it pushes through the soil and matures into a fully formed onion. The onion is ready to harvest when the outer layers of the bulb are dry and the stem has withered.


Understanding Germination

The onion seed begins its journey, absorbing water and sprouting. This is the first stage of growing onions, called germination. It’s when the potential is unlocked, and the tiny seed grows into a robust and healthy plant. All begins with the right conditions: temperature, moisture, and seed quality are crucial in this stage.

The Role of Conditions in Germination

During germination, the onion seed absorbs water, the root emerges, and a shoot develops. The germination process can vary in length depending on a few factors, like temperature, moisture, and seed quality. It’s a delicate dance, balancing these elements to create the perfect environment for your onion seeds. On average, onion seeds take around 7 to 10 days to germinate.

Onion germination
Onion germination


When you see that first little sprout pushing its way through the soil, it’s a sign that your onion seeds have successfully germinated. At this point, the seed has transformed into a seedling, ready to continue its growth journey. After this process, it’s time to prepare for the next stage: the seedling stage.

Conclusion: The Vital First Stage

The germination stage is a vital part of onion growth. It’s the first step in the plant’s life cycle and sets the stage for all the growth to follow. From the moment the seed absorbs water and starts to sprout to the root’s emergence and the shoot’s development, every step in the germination process is crucial. By understanding this stage and providing the right conditions for your onion seeds, you’re setting yourself up for a successful harvest.

The Seedling Stage

From the moment the first signs of life emerge from the germinated onion seed, it is called the seedling stage. This is an exciting and critical period in the onion’s life cycle as it establishes itself and prepares for future growth. During this stage, the seedling develops its first set of true leaves and shows a more robust root system, setting the tone for a healthy and robust onion plant.

Unfold the following things In the seedling stage

The seedling’s first true leaves spring into life. These differ from the initial sprouts that broke through the soil during germination. True leaves signify that the seedling is maturing and preparing to enter the vegetative stage.

The root system grows more potent and more complex. This is essential for the onion plant’s survival, as the roots absorb water and nutrients from the soil.

Seedling stage
Seedling stage

The duration of this stage can vary, ranging from a few weeks to a couple of months. This variance largely depends on sunlight, moisture, and nutrient availability.

It’s crucial to provide the seedlings with the right conditions for growth during this stage. That means:

Ensuring they get adequate sunlight. Onions are sun-loving plants, so ensure your seedlings are placed somewhere they can bask in plenty of light.

I am keeping the soil moist but not waterlogged. Overwatering can lead to root rot, while underwatering could cause the seedlings to dry out and die.

We are providing the proper nutrients. Onions require fertile soil packed with nutrients. If your soil is lacking, consider adding a slow-release organic fertilizer.

In conclusion, the seedling stage is pivotal in the onion’s life cycle. It’s a time of growth and development where the foundations for a healthy and productive onion plant are laid.

The Vegetative Growth Stage of Onion

Once the seedling stage is complete, we move on to the third stage of the journey, called the vegetative stage. This is when your onion plant experiences a surge in growth and starts to develop a bulb, which is the part we all use in our cooking. This phase is vital in establishing a robust and healthy plant structure, setting the stage for a promising harvest.

  • 1. During the vegetative stage, you will notice an increase in the development of leaves. Each leaf your onion plant produces at this time represents a ring in the future bulb. This implies that the more leaves your plant has, the larger the bulb will be. So, if you dream of big, juicy onions, this is the time to encourage as much leaf growth as possible.
  • 2. As you might have guessed, supporting such growth isn’t a passive task. Your onion plants will need plenty of sunlight, water, and nutrients during this period. Regular watering is crucial, especially during dry periods. Onions are shallow-rooted and can dry out quickly. Do not overwater, as onions prefer to be waterlogged. A balanced fertilizer can also help support leaf and bulb growth, enhancing your plant’s size and overall health.
  • 3. Various factors, including the onion variety and the specific growing conditions, impact the length of the vegetative stage. Some onion types may progress faster than others, and external factors such as temperature, soil type, and even the latitude of your garden can significantly affect growth rates. It’s essential to be mindful of these factors and adjust care as necessary to support your plants through this critical period of growth.

In conclusion, the vegetative stage is a crucial phase in onion cultivation. It is where we encourage healthy leaf development and start to see the formation of our desired onion bulbs. It is an exciting time when our hard work begins to pay off, laying the groundwork for a bountiful harvest. With careful attention to watering, nutrient supply, and environmental conditions, you can help your onion plants thrive during this stage.

Vegetative stage of onion growth stages
Vegetative stage of onion growth

Bulb Formation and Maturation

After the vegetative stage, our onions enter the exciting stage of bulb formation. Environmental variables like day length, temperature, and soil conditions drive this bulb initiation phase. The bulb increases in size and weight during this phase, gradually transforming into the delicious onion we eagerly await harvest.

The onion matures when the neck folds, the external skin changes color, and the foliage withers away. The change in skin color and foliage indicates that our onion is ready for the next stage, called harvesting.

Bulb Formation stage of onion growth
Bulb Formation

The time it takes for onions to reach maturity can vary. Several factors, such as the type of onion, growing conditions, and the cultivation method, can influence this. Generally, it takes around 90 to 120 days for an onion to mature from an onion cutting.

Onions can be harvested at any stage, even while they are still seedlings. However, for fully mature bulbs, you must wait until about half of the top leaves have warped and the bulb skin has a papery feel. If you let the bulbs stay in the ground until 49 percent or more of the green tops have collapsed, they will store longer.

Maturation stage of onion growth

Harvesting Mature Onions

The Right Time to Harvest

When it comes to harvesting onions, timing is everything. As I mentioned, onions are usually ready for harvest when about half of their leaves have bent, and the bulb’s skin has a papery texture. A standard error many novice gardeners make is harvesting too early or too late, which can severely impact the onion’s flavor and storage life. Harvesting is best when the leaves have wholly withered and turned brown.

The Harvesting Phase

The process of harvesting onions is simple but requires precision. You don’t want to damage the bulbs as it can decrease their longevity in storage. Begin by gently loosening the soil around the onion using a fork or spade, taking care not to pierce the onion itself. Once the soil is loose, you can pull the onion out or cut it at ground level.

Harvesting stage of onion growth
Harvesting stage

Post-Harvest Handling

After you’ve harvested your onions, handling them with care is essential. Just pulled out of the earth, they are still quite delicate and can be easily damaged. Avoid leaving freshly harvested onions in the sun for too long, as this could cause them to wither or become sunburned. Instead, please place them in a shaded, dry, and well-ventilated area to allow them to cure.

Curing and Storing

Curing is an essential part of the post-harvest process and is vital for ensuring your onions have a long storage life. This process involves drying out the onions to remove any excess moisture, which can lead to rot. It typically takes around two weeks for onions to cure fully. Once the onions are properly cured, they can be stored in a cool, dry place. Ideally, onions should be stored in a mesh bag or other breathable container to prevent moisture buildup.

Curing and storing of onion
Curing and storing of onion


In conclusion, understanding the onion growth stages is fascinating and highly beneficial, especially if you’re into gardening or farming. From the germination stage, where the tiny seeds break open to give rise to a new plant, to the seedling stage, where the young onion plants start developing leaves, every stage is unique and critical. Then, we have the vegetative stage, where the plant proliferates and prepares for bulb formation.

The bulb formation and maturation stages are exciting. Here, the onion starts creating the bulb we commonly use in our kitchens. This stage requires patience as it takes time for the bulbs to grow and mature. Finally, the harvesting stage comes when our efforts pay off, and we collect our ripe, juicy onions ready to spice up our dishes.

What are the primary stages of onion growth?

There are five main stages germination, seedling, vegetative, bulb formation, maturation, and harvest

What happens during the germination stage?

   During germination, the onion seeds absorb water and nutrients from the soil, developing a sprout that breaks through the seed’s shell and grows upward.

What is the seedling stage of onion growth?

   The seedling stage of onion growth is when the onion sprout develops its first leaves. This stage is critical as the plant begins photosynthesizing and generating energy for further growth.

What is the vegetative stage in onion growth?

   In the vegetative stage, the onion plant focuses on producing a strong, leafy green top. The health of the green top is crucial as it affects the size of the onion bulb that will eventually form.

How are bulb formation and maturation in onion growth?

   The formation and maturation of the bulb occur when the onion plant has sufficiently developed its green top. The plant begins channeling energy into developing a bulb, which grows and matures until it’s ready to harvest.

When is the ideal time to harvest mature onions?

   The best time to harvest onions is when the green tops have fallen over and turned brown. At this stage, the bulbs have completed their growth.

Why is understanding the stages of onion growth critical?

   Understanding the stages of onion growth allows a gardener or farmer to ensure optimal conditions for each stage, ultimately leading to a successful, healthy harvest. This understanding is critical for predicting the crop’s lifecycle and making timely interventions when necessary.



Hi, I am Sikandar Mehdi, founder of mybestvegetables.com. I have been a professional farmer for 20 years. After graduating in 2002, I started learning about vegetables. After a lot of experience, in 2023, I started sharing my blog on my platform, mybestvegetables.com.

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